Best Cat Scan Registry Review

Front 1

Computed Tomography, or CT, has been commonly called_______________ or_________________ in the past.

Back 1

Computerized Axial Tomography, CAT-Scan

Front 2

Where are the instructional commands entered by the technologist?

Back 2

The CT System Control

Front 3

List five types of information/ instructions that are entered at the CT System Console.

Back 3

1) Patient Information
2) Imaging Parameters
3) Post-Processing Technique
4) Filming
5) Archiving

Front 4

What CT System Component translates each command as it is entered into the systems machine language before passing it on to the Scan controller?

Back 4

The Host Computer

Front 5

What does the scan controller do?

Back 5

It is responsible for the timing and operation of the table, gantry, and high voltage generator.

Front 6

Which system Components operate using analog waveform?

Back 6

The table, gantry, and high voltage generator.

Front 7

What is another name for analog waveform

Back 7

Continuous waveform

Front 8

What CT System Component is responsible for converting the digital signal into an analog form?

Back 8

The Digital-To-Analog Converter or DAC

Front 9

What does DAC stand for?

Back 9

Digital-To-Analog Converter

Front 10

What are the two most notable components located in the gantry?

Back 10

The xray tube and the detectors

Front 11

What CT System Component is necessary to produce the high voltage potential that exists between the cathode and the anode?

Back 11

The High Voltage Generator

Front 12

What gantry component collects the attenuation information?

Back 12

The Detectors

Front 13

What do the detector elements do?

Back 13

They measure the attenuation information coming out of the patient and convert it into tiny electrical signals that are then sent to the amplifier.

Front 14

Where is the tiny electrical signal output from the detector elements sent?

Back 14

To the Amplifier

Front 15

In what electrical form does the amplifier output its signal/ information?

Back 15

In Analog form

Front 16

Where does the analog signal go to after it leaves the amplifier component?

Back 16

To the Sample-and-Hold Component (S/H)

Front 17

Where is the data stored after it leaves the DAC?

Back 17

In the raw data file

Front 18

In which system component is data calculated into an image?

Back 18

The Array Processor

Front 19

Where does the calculated image go to after it leaves the Array Processor and what for?

Back 19

The calculated image goes to the Host Computer so that it may be maintained on a storage device and displayed on the console monitor.

Front 20

Where does the analog signal go to after it leaves the Sample-and-Hold Component?

Back 20

To be digitized by the Analog-to-Digital Converter or ADC.

Front 21

When was the 1st CT System commercially introduced for general clinic use?

Back 21

1973

Front 22

How many Generations of CT Systems are there?

Back 22

4

Front 23

First generation CT Systems generated a thin, focused x-ray beam called what?

Back 23

A "Pencil Beam"

Front 24

How many detectors were incorporated in the 1st generation CT Systems?

Back 24

One

Front 25

What was it called when the Tube/Detector configuration in a 1st Generation Scanner scanned across the patient's body in a linear path before rotating and repeating?

Back 25

It "Translated"

Front 26

In a 1st generation scanner, what did you call the series of measurments the was collected as the tube/ detector assembly translated across the patient?

Back 26

A "Projection"

Front 27

What is the 1st Generation defination of a Projection?

Back 27

A series of measurments collected as the tube translates across the patient.

Front 28

1st Generation: What happens next after a complete translation from one side of the patient to the other?

Back 28

The tube/detector assembly rotates about the patient 1 degree and another translation commences so that another "projection" can be measered.

Front 29

How many different projection were need in a 1st generation system in order to construct and image?

Back 29

180
(180 degree arc)

Front 30

What was the shortest possible scan time per image with a 1st Generation system?

Back 30

5 minutes per image

Front 31

Since 1st Generation Scanners were so slow, imaging was limited to what part of the body and why?

Back 31

Head because patient motion could be more easily controlled

Front 32

List four key aspects of 1st Generation CT Scanners?

Back 32

1) Pencil Beam
2) Single Detectors
3) The tube/detector assembly translated, rotated 1 degree and repeated
4) Scan Time was 5 minutes per image

Front 33

2nd Generation CT Systems used an x-ray tube that produced an x-ray beam that had a shape similar to what?

Back 33

Opened paper fan

Front 34

2nd Generation Systems are referred to as having ________ Geometry.

Back 34

"Fan Beam"

Front 35

2nd Generation Systems contain a/an __________ of detectors referred to as a/an_______________?

Back 35

group, detector array

Front 36

About how many detectors comprised the detector array in 2nd Generation Systems?

Back 36

About 30

Front 37

What was the purpose of the added detectors (detector array) and the fan beam geometry in the 2nd Generation design?

Back 37

To reduce the amount of time required to collect data.

Front 38

How much faster could a 2nd Generation Scanner collect the required data compared to a 1st Generation Scanner?

Back 38

About 10 times faster

Front 39

True/False: In regards to 2nd Generation Systems, the tube/detector assembly still translated across the patient during the collection of a "projection" of data.

Back 39

True

Front 40

After a "projection" of data is obtained in a 2nd Generation System, the tube/detector rotates typically ___________ covering an arc of __________ around the patient.

Back 40

5 degrees or more, 180 degrees

Front 41

What was the scan time for a single image in a 2nd Generation Scanner?

Back 41

As little as 20 seconds

Front 42

What single aspect of 2nd Generation Scanners led to applications outside the head?

Back 42

The reduced scan time. (From 5 minutes on a 1st Generation Systems to 20 seconds per image on a 2nd Generation Systems)

Front 43

What were the 2 most important features of 2nd Generation Scanners which quickly made 1st Generation Systems obsolete?

Back 43

1) Fan beam geometry
2) The detector Array

Front 44

List four key aspects of 2nd Generation Systems.

Back 44

1) Fan Beam
2) Multiple detectors in a straight line
3) Tube/Detector moved across the patient then rotated by approx. 5 degrees
4)Total scan time of about 20 seconds per image

Front 45

When were 3rd Generation Systems first introduced?

Back 45

1975

Front 46

Most Ct Scanners made today still apply similar technologies as those incorporated in which generation of CT Systems?

Back 46

3rd Generation Systems

Front 47

3rd Generation Systems incorporate what type of beam geometry?

Back 47

Fan Beam Geometry

Front 48

The tube/detector array in a 3rd Generation Systems no longer _____________ as a 1st and 2nd Generation Systems but simply __________ around the patient.

Back 48

translates, rotates

Front 49

What was the major difference in the configuration between 2nd and 3rd Generation Systems?

Back 49

The 3rd Generation detector array in a curved arc rather than a straight line.

Front 50

Why was the curved detector array contained in 3rd Generation Systems an improvement over 1st and 2nd generation designs?

Back 50

-It improved the reproducibility of the "projection data measured across the array.
-It also minimized certain artifacts that were common in 2nd Generation Systems.

Front 51

Most scanners today are based on ____________ technology.

Back 51

3rd Generation

Front 52

How many detectors are contained in a 3rd Generation Systems detector array?

Back 52

The number of detectors in a 3rd Generation Systems has ranged from several hundred to several thousand.

Front 53

The term "scan" slightly changed meaning with the introduction of 3rd Generation Systems. Why?

Back 53

Because the tube/detector array no longer had to "translate" across the patient.

Front 54

What is today's defination of a "scan"?

Back 54

The collection of anatomical information during the time the xray beam is on.

Front 55

How fast can a 3rd generation system acquire the data for one image?

Back 55

Faster than one second per image.

Front 56

List the four key aspects of a 3rd generation CT system.

Back 56

1.) Fan Beam
2.) Multiple detectors along and arc
3.) The tube/detector assembly rotates around the patient ( without translating)
4.) Total scan time faster than 1 second per image

Front 57

Why were 4th generation systems developed?

Back 57

As an alternative technology to 3rd generation systems

Front 58

What is the beam geometry of a 4th generation system?

Back 58

Fan Beam

Front 59

Describe the detector arrangement in a 4th generation CT system.

Back 59

The detectors do not travel with the tube but instead form a complete circle around the gantry in a ring configuration, which nutates or angles during the scanning process.

Front 60

What does nutate mean?

Back 60

To angle

Front 61

T/F: Many more detectors are required in 3rd generation scanners than 4th generation scanners.

Back 61

False; many more detectors are required in 4th generation scanners than 3rd generation scanners.

Front 62

T/F: 4th generation systems did not necessarily represent a design which was more advanced than 3rd generation systems or that offered improved clinical benefits.

Back 62

True

Front 63

T/F: 3rd and 4th generation systems use different approaches to achieve similar results.

Back 63

True

Front 64

T/F: Today there are very few scanners that use 4th generation technology.

Back 64

True

Front 65

List the four key aspects of 4th generation CT systems.

Back 65

1.) Fan Beam
2.) Multiple detectors encircle the patient and do not rotate around the patient.
3.) Only the tube rotates around the patient
4.) Total scan time of 1 second per image or faster.

Front 66

T/F: In the early days of 3rd generation systems, the high voltage generator was large and heavy and was safely fastened to the floor in the exam room.

Back 66

True

Front 67

In the days before continuous rotation scanners, what transferred the high voltage from the generator to the x-ray tube?

Back 67

A large, bulky, high tension cable

Front 68

In the early days of 3rd generation scanners, before the invention of continuous rotation scanners, shy was it necessary to stop the gantry frame from rotating at the end of every scan and then reverse the direction of the gantry frame’s rotation for the next scan?

Back 68

To prevent the high-tension cable going from the High Voltage Generator to the tube from winding up

Front 69

Why were continuous rotation scanners introduced?

Back 69

To speed up the exam process

Front 70

Most continuous rotation scanners use ______________ technology.

Back 70

Slip Ring

Front 71

What is the slip Ring?

Back 71

The slip ring is a large rotating ring which surrounds the gantry aperture and, by means of electrical brushes, conveys electrical power and data to the components mounted on the rotating ring.

Front 72

Why was slip ring technology such an improvement over existing technology?

Back 72

Because it eliminated the winding up of the high tension cable and allowed for faster exam times due to the eliminated need for reversal of the gantry frame rotation between scans

Front 73

What was the single most important advancement that led to the development of helical imaging?

Back 73

The introduction of continuous rotation scanners

Front 74

What is another name for helical imaging?

Back 74

Spiral Imaging or Spiral CT

Front 75

What is another name for conventional scanning?

Back 75

Serial Scanning

Front 76

Did Continuous Rotation and Multi-row Detector scanners come out at about the same time?

Back 76

No; Multi-row Detector scanners came out years after continuous rotation scanners were the norm.

Front 77

What are the only two ways to cover anatomy faster in a helical study with a single row detector scanner?

Back 77

1.) Increase the slice thickness
2.) Vary the pitch

Front 78

What does MDCT stand for?

Back 78

Multi Detector Computed Tomography

Front 79

What are other names for MDCT?

Back 79

1.) Multi-Slice Scanners
2.) MSCT
3.) Multi-Array Scanners

Front 80

What type of architecture do MDCT scanners have?

Back 80

3rd Generation

Front 81

What are the three things that are transferred by the slip ring?

Back 81

1.) Electrical Power
2.) Scanning Instructions
3.) Detected Signals

Front 82

How many detectors are contained in a single detector array of a 3rd generation system?

Back 82

Several hundred

Front 83

List the benefits of MDCT.

Back 83

1.) Faster Scans
2.) Increased anatomical coverage
3.) The ability to use thinner slices to improve resolution along the slice direction

Front 84

What does EBCT stand for?

Back 84

Electron Beam Computed Tomography

Front 85

When was EBCT originally designed?

Back 85

In the mid-1980’s

Front 86

T/F: EBCT does not use an x-ray tube.

Back 86

True

Front 87

How does EBCT work?

Back 87

An electron gun produces an electron bean which is electro-magnetically directed toward an array of tungsten anodes located around the patient. X-Rays are then generated from the collision of electrons and the tungsten anode.

Front 88

What is the fastest CT on the market?

Back 88

EBCT

Front 89

How long does one “rotation” take on an EBCT scanner?

Back 89

50 to 100 milliseconds

Front 90

The speed of EBCT makes it well suited for doing what?

Back 90

Imaging the heart and coronary arteries.

Front 91

What do we call the comparison of two imaging modalities yielding co-registered images?

Back 91

Fusion Imaging

Front 92

What are the two most common modalities to fuse?

Back 92

CT and PET

Front 93

What does PET stand for?

Back 93

Positron Emission Tomography

Front 94

Where does the radioactive pharmaceutical used in PET accumulate after it is injected?

Back 94

In tissues having areas of rapid growth and increased metabolism

Front 95

T/F: Pet images are very sensitive to changes in metabolism associated with malignant tissues but have very poor resolution.

Back 95

True

Front 96

Why is there such great value in PET/CT scans?

Back 96

Because it shows the exact location of metabolism changes (tumors/growth) based off the high resolution CT images that are registered to the PET images.

Front 97

T/F: When PET and CT are fused, the studies can occur on different days.

Back 97

True

Front 98

What are the advantages of having a duel modality PET/CT scanner?

Back 98

1.) Acquiring the PET/CT images back to back w/out any patient motion makes it easier to register the PET and CT images accurately.

2.) Information from the CT scan simplifies a necessary step performed on the PET study known as Attenuation Correction.

Front 99

What is being used in the oncology department in order to verify patient positioning prior to receiving radiation therapy?

Back 99

Cone Beam CT

Front 100

T/F: Cone Beam CT, used in oncology acquires up to 64 slices per rotation.

Back 100

False: Cone Beam CT, used in Oncology, does not acquire individual slices, but instead collects data w/a large 2D panel to acquire the entire volume of anatomical information in 1 rotation.

Front 101

T/F: Cone Beam CT is being used in dental and scientific imaging.

Back 101

True

Front 102

What system component is the key point of interaction between the technologist and the imaging system?

Back 102

The Operators Console

Front 103

What types of information/commands can be initiated from the operators console?

Back 103

1.) Patient Information
2.) Imaging Parameters
3.) Post Processing Commands
4.) Image Manipulation

Front 104

What are two examples of Graphic Input Devices?

Back 104

1.) A Mouse
2.) A Trackball

Front 105

What console component serves the purpose of providing feedback to the technologist and data entry?

Back 105

The Monitor

Front 106

What system component is the primary link between the technologist and the other components of the imaging system?

Back 106

The Host Computer

Front 107

What component controls the storage devices such as hard disks and removable media?

Back 107

The Host Computer

Front 108

The patient table is fed threw the ___________ of the gantry.

Back 108

Aperture

Front 109

On most current CT systems, the ________ and _________ are also contained within the gantry.

Back 109

Slip Ring, HVG (High Voltage Generator)

Front 110

The _____________________ is located toward the central aspect of the gantry, about the perimeter of the gantry aperture.

Back 110

Rotating Frame Assembly

Front 111

The rotating frame assembly contains the _________, ____________ and the ___________.

Back 111

tube, detector array, data acquisition system (DAS)

Front 112

Direct acquisition of the oblique slices may be collected when the gantry is oriented in an orientation between ______________ and _____________.

Back 112

Transverse and Coronal

Front 113

How much can a gantry tilt/angle?

Back 113

Approximately 30˚ from the vertical plane

Front 114

The patient most often lies in the ________ position.

Back 114

Supine

Front 115

What do we call the hole in the gantry where the table is fed through?

Back 115

The gantry “Aperture”

Front 116

In what two types of scans does the table move continuously while scanning?

Back 116

1.) Helical Scans
2.) Localizer Image (Scout)

Front 117

Describe the Patient Coordinate System.

Back 117

x-axis: The axis extending from the patients left to right side. (left to right)
y-axis: The axis extending from anterior to posterior through the patient. (anterior to posterior)
z-axis: The axis extending along the patient table and the long axis of the patients body. (head to feet)

Front 118

Where is the CT x-ray tube mounted?

Back 118

On the Rotating Frame Assembly within the gantry

Front 119

T/F: Electrons are atomic particles that have a positive charge.

Back 119

False: Electrons have a negative charge

Front 120

What are the three possible paths that a fast moving electron may take as it passes through an atom?

Back 120

1.) Directly collide with nucleus. (unlikely) (Bremsstrahlung)
2.) Enter the vicinity of the nucleus and loose energy, slowing down, changing direction and emitting Bremsstrahlung radiation.
3.) Collide with an electron in an inner shell of the target atom. (Characteristic)

Front 121

How is Bremsstrahlung radiation produced?

Back 121

1.) When an incoming electron collides with the nucleus of an atom and loses much of it’s energy and x-ray photon is produced. (Very unlikely)
2.) When an incoming electron enters the vicinity of the nucleus of an atom and looses energy, slowing down and producing a Bremsstrahlung photon.

Front 122

What is another name for Bremsstrahlung Radiation?

Back 122

Breaking Radiation

Front 123

Why is it called Characteristic Radiation?

Back 123

Because the energy level of the emitted photons is a characteristic of the specific target atom.

Front 124

What percentage of the x-ray beam emitted from a CT x-ray tube is Characteristic Radiation

Back 124

10%-12%

Front 125

What do we call the voltage applied across the anode and the cathode?

Back 125

The “Tube Voltage”

Front 126

mA is a measurement of what?

Back 126

The “Filament Current”

Front 127

The quality of x-rays emitted from the anode target is _________ to the number of electrons which stream from the __________ to the anode.

Back 127

proportional, filament

Front 128

What are the normal ranges in CT for mA and kVp?

Back 128

mA: Tens to Hundreds of mA
kVp: 90-140kVp

Front 129

What does the “Space Charge Compensator” do?

Back 129

It cools off the filament slightly as the tube voltage increases in order to prevent an unwanted elevation in tube current in response to higher kV levels.

Front 130

What do we call the flow of electrons from cathode to anode?

Back 130

The Tube Current

Front 131

What is the main source of the enormous amount of heat that builds up in a CT x-ray tube?

Back 131

The generation of x-rays from the collision between the electrons and the anode target.

Front 132

What is the atomic number of tungsten?

Back 132

74

Front 133

What is the melting point of tungsten?

Back 133

Approximately 3400˚ C

Front 134

What is located on the surface of the rotating anode?

Back 134

Tungsten

Front 135

The cathode of most CT x-ray tubes contains more than one __________, each with a __________ __________.

Back 135

filament, different length

Front 136

What determines which filament is actually used in an exam?

Back 136

The size of focal spot that is required for the exam

Front 137

What CT x-ray tube component makes thin slice, high resolution imaging possible.

Back 137

The availability of a small focal spot, which comes from having/using a small filament.

Front 138

What is the minimum amount of time that must transpire between the end of one scan and the initiation of the next scan called?

Back 138

The “Inter-scan Delay Time”

Front 139

Restricting the lower energy photons from entering the patient minimized an undesirable effect called _________ ________ as well as the _________ _________.

Back 139

Beam Hardening, Patient Dose

Front 140

What is the only part of the tube that passes x-rays?

Back 140

The Tube Window

Front 141

T/F: Inter-scan delay times include idle time between scans to allow tube cooling.

Back 141

True

Front 142

What are the two types of collimators that exist in CT scanners?

Back 142

1.) Pre-Patient
2.) Post-Patient

Front 143

What do pre-patient collimators do in single-row detector scanners?

Back 143

They restrict the x-ray beam to the thickness of the slice.

Front 144

What do pre-patient collimators do in multi-row detector scanners?

Back 144

They select the thickness of the x-ray beam, which spreads out over multiple detectors.

Front 145

What are the thick, metal pre-patient collimators attached to?

Back 145

To the bottom of the tube housing

Front 146

What is the purpose of collimation?

Back 146

1.) Reduce the dose to the patient
2.) Reduce the production of scatter radiation

Front 147

T/F: Pre-patient collimation is a factor in determining the slice thickness in single-row detector CT, but not in MDCT.

Back 147

True

Front 148

What is another name for post-patient collimation?

Back 148

Pre-Detector Collimation

Front 149

What are the two functions of post-patient collimators?

Back 149

1.) To provide better definition to the slice thickness on single-row detector scanners.
2.) To reduce the amount of scatter radiation that would otherwise enter the detector system.

Front 150

What are the three conditions required for the detectors used in a CT system to measure an incoming photon?

Back 150

1.) Enter the detector – be “Captured”
2.) Collide with a detector – be absorbed
3.) Produce a measurable result

Front 151

What are the two basic categories of detectors?

Back 151

Gas and Solid State detectors

Front 152

Most gas detectors used on CT systems contain a gas called _________.

Back 152

Xenon

Front 153

How big is the opening in each xenon gas detector?

Back 153

Approximately 1mm

Front 154

What is done to a xenon gas chamber in order to increase the chance of an incoming x-ray photon interacting with the gas inside?

Back 154

It is pressurized up to 30 times the normal atmospheric pressure

Front 155

What happens to a xenon atom when it is struck by a photon?

Back 155

It splits into an ion and an electron.

Front 156

What happens to the xenon atom after it splits?

Back 156

One side plate of each detector chamber has a positive charge and the other has a negative charge. After the collision the two charged particles migrate to the plate with the opposite charge and this can be measured as an electrical event.

Front 157

The xenon detector is most sensitive to x-rays coming from which direction and why?

Back 157

-To x-rays entering the detector straight on.
-Because the detector has the shape of a narrow, tall chamber

Front 158

Which type of detector provides it’s own inherent post-patient collimation and why?

Back 158

The Xenon Gas detector- Because of its relative insensitivity to x-rays striking it at severe angles

Front 159

Why can’t xenon detectors be used in fourth generation systems?

Back 159

Because they aren’t sensitive to x-rays entering the chamber from any other direction than strait-on.

Front 160

T/F: Xenon gas detectors cannot be used in 4th generation systems.

Back 160

True

Front 161

What is the current detector of choice?

Back 161

Solid State Detectors

Front 162

What is another name for solid state detectors?

Back 162

Scintillation Detectors

Front 163

What is a solid state detector made of?

Back 163

A solid crystalline substance which is much more dense than Xenon.

Front 164

T/F: The size of a solid state detector is about the same size as a xenon gas detector.

Back 164

True

Front 165

T/F: The collision between the photon and the detector atom occurs much closer to the surface in a solid state detector than a xenon gas detector.

Back 165

True

Front 166

Which type of detector is the most sensitive to x-rays coming in from various angles?

Back 166

A Solid State Detector

Front 167

T/F: Solid state detectors have been used on both 3rd generation and 4th generation scanners.

Back 167

True

Front 168

Which type of detector generates a flash of light in response to an incoming x-ray photon?

Back 168

Solid State

Front 169

When a solid state detector generates a flash of light, it is sensed by the ______________.

Back 169

Photodiode

Front 170

Describe how a solid state detector works.

Back 170

When a photon strikes the solid state material, it emits a flash of light which is converted into an electrical signal by a photocathode.

Front 171

Where is the photodiode located?

Back 171

It is attached to the bottom of the solid state material on the detector.

Front 172

T/F: The signal from both xenon and solid state detectors must be amplified.

Back 172

True

Front 173

On single row detector scanners, what determines the final slice thickness?

Back 173

The collimation

Front 174

How is the acquired slice thickness calculated on an MDCT Scanner/

Back 174

Acquired slice thickness = The thickness of the x-ray beam # of slices acquired per rotation

Front 175

In MDCT scanners, what are the two basic types of detector arrays?

Back 175

1.) Symmetric
2.) Asymmetric

Front 176

Where is the primary place for all complex mathematical calculations involved in generating CT images?

Back 176

The Array Processor

Front 177

What is the primary function of the array processor?

Back 177

The reconstruction of the projected attenuation raw data into a CT image

Front 178

The array processor is also the site of calculations required to generate __________ ____________, and sometimes, to __________ image data.

Back 178

Retrospective reconstructions, post-process

Front 179

Define “Digital Image”.

Back 179

A “Digital Image” is a numerical representation of an object that can be recognized and processed by a computer.

Front 180

What do we call each small region of a digital image’s grid/

Back 180

A Picture element or Pixel

Front 181

The grid of pixels comprises the _______ ________.

Back 181

image, matrix

Front 182

Define an “Integer”.

Back 182

A positive (+) or negative (-) whole number

Front 183

What does the digitizing process involve?

Back 183

An integer is assigned to each amplified electrical signal. The value of the integer is determined by the signal’s strength. The stronger the electrical signal, the larger the integer. Each integer also corresponds to a shade of gray in the image. This allows the display hardware to assign a specific gray level to the region of a CT image from which this attenuation information was detected.

Front 184

Explain the word “Projection”.

Back 184

A projection can be taught of as a “view” of the anatomical cross-section from a particular vantage point.

Front 185

What does the display hardware do?

Back 185

It assigns a specific gray level to the region of a CT image from which the attenuation information was detected.

Front 186

What word associated with Computed Tomography is synonymous with the word “View”?

Back 186

Projection

Front 187

List three Scanning Methods

Back 187

1.) Localizer
2.) Conventional, or serial, CT
3.) Helical CT

Front 188

The Localizer scan is similar to a ______ ________ radiograph.

Back 188

plain film

Front 189

What are the two most common orientations for localizer scans?

Back 189

•AP
•Lateral

Front 190

Which scanning method entails the x-ray tube rotating around the patient while the patient table remains stationary?

Back 190

Conventional, or serial, CT

Front 191

What is another name for helical or spiral CT?

Back 191

Volumetric CT

Front 192

T/F: The localizer image has limited resolution due to the size and spacing of detector elements, and requires longer exposure times than conventional radiography.

Back 192

True

Front 193

Conventional radiography images tend to have better tissue contrast compared to CT localizer images.

Back 193

False: CT localizer images have better soft tissue contrast than conventional images.

Front 194

Why do CT localizer images have better soft tissue contrast than conventional films?

Back 194

Because of the reduction in scatter radiation as a result of pre-patient and post-patient collimation.

Front 195

T/F: The localizer image has limited resolution due to the size and spacing of detector elements.

Back 195

True

Front 196

T/F: Since a single projection is used, there is no need for a complex reconstruction technique on localizer images.

Back 196

True

Front 197

When is a lateral localizer image obtained?

Back 197

In general, only if we intend to angle the gantry to specify oblique slices (e.g., for some head and spine studies)

Front 198

What scanning method is the “Gold Standard” for CT image Quality?

Back 198

Conventional or Serial Scanning.

Front 199

T/F: Conventional CT yields the best image quality which is free from helical artifacts.

Back 199

True

Front 200

Give three examples of where Conventional CT is the preferred scanning method of choice and explain why.

Back 200

1.) Some neurological exams such as studies involving the temporal bones; because it demands fine detail
2.) Cases involving obese patients
3.) Cardiac calcium scoring studies; because it mimics the results that would be obtained from EBCT

Front 201

For a ________ ______, projections are made throughout the ____________ _____ rotation.

Back 201

full scan, complete 360˚

Front 202

Data measured at each projection is placed in a computer file called the _____ ______.

Back 202

Raw Data

Front 203

Each projection can consist of how many measurements coming from the detectors?

Back 203

Several hundred

Front 204

If a single row detector scanner has 750 detectors in its detector array, how many attenuation measurements would be gathered from one projection?

Back 204

750 attenuation measurements

Front 205

How many individual projections might be obtained during one full rotation (360˚)?

Back 205

1500

Front 206

If there are 750 detectors in the detector array and 1500 projection are collected per rotation, how many attenuation measurements would be collected for one image?

Back 206

1,125,000 attenuation measurements would be collected

Front 207

If a 64 slice MDCT scanner has 850 detector elements in a single array and there are 1700 projections collected per full rotation, how many total attenuation measurements are collected per rotation?

Back 207

92,480,000 measurements/samples

Front 208

A _________ _____ allows for continuous data collection during continuous patient movement through the gantry.

Back 208

helical scan

Front 209

T/F: One benefit of helical scanning is that a smaller amount of contrast media may be used for many procedures.

Back 209

True

Front 210

_________ __________ and _________ studies were the first exams to be routinely acquired with a helical technique.

Back 210

Chest, abdomen and pelvis

Front 211

List six advantages of helical scanning.

Back 211

1.) Faster Studies
2.) More coverage in a breath-hold
3.) No missed anatomy
4.) Less contrast agent needed
5.) Arbitrary slice positioning
6.) Ideal dada for post-processing

Front 212

In helical imaging, the path of the x-ray beam is determined by the thickness of the _______ ________ and the speed of the _________ _______.

Back 212

x-ray beam, patient table

Front 213

The thickness of the x-ray beam in a helical study is determined by the ___________ _____________.

Back 213

pre-patient collimation

Front 214

What is the extra step involved in helical image reconstruction?

Back 214

A mathematical calculation has to be ran on the helical raw data in order to divide it into individual, planar data slices that can then be reconstructed into images using the same mathematical process applied to conventional image data sets.

Front 215

Most CT systems today use a reconstruction method called _______ _____ __________.

Back 215

Filtered Back Projection

Front 216

What are the two steps to filtered back projection?

Back 216

1. Applying a filter to the raw data
2. Back projection

Front 217

Define “Back Projection”.

Back 217

Back Projection is a technique which adds together the attenuation information collected from all of the projections.

Front 218

What would happen if you did not filter the back projection?

Back 218

The image would have blurry edges and appear very “grainy” or “noisy”

Front 219

Explain the “filtered” in filtered back projection.

Back 219

It refers to a filter that enhances certain characteristics in the raw data before back projection is performed.

Front 220

What do we call the filter that is applied to the raw data during image reconstruction?

Back 220

A reconstruction filter or kernel

Front 221

What is the process of applying a filter to the raw data called?

Back 221

Convolution

Front 222

What is the purpose of a reconstruction filter, or kernel?

Back 222

To enhance the important characteristics of the image before back projection is performed

Front 223

What are the two basic types of reconstruction filters?

Back 223

Sharp and smooth

Front 224

What does a sharp reconstruction filter do?

Back 224

It improves the definition of the edges of structures but it does not minimize the grainy or speckled appearance in the image.

Front 225

What does a smooth reconstruction filter do?

Back 225

It minimizes the grainy appearance of noise in the image so that the contrast between tissues can be better distinguished, but is does not improve upon the edge definition.

Front 226

What do we call the attenuation information collected at each projection?

Back 226

Attenuation profiles

Front 227

T/F: In general, sharp filters are used when examining predominantly low contrast regions, such as the abdomen and brain.

Back 227

False: Sharp filters are used when examining predominantly high contrast regions, such as in musculoskeletal studies.

Front 228

T/F: Smooth filters are preferable when examining low contrast regions, such as the abdomen and brain.

Back 228

True

Front 229

T/F: If back projection was applied to the raw data without convolution, the tissues I the resulting image would have blurry edges and they would be difficult to differentiate because they would appear grainy or noisy.

Back 229

True

Front 230

At about what thickness does an x-ray beam cease to be referred to as a fan beam and start being referred to as a cone beam?

Back 230

At about 20mm

Front 231

If standard filtered back projection is applied to a cone beam, this results in an artifact known as a/an _____________________.

Back 231

Cone Beam Artifact

Front 232

Describe a Cone Beam Artifact.

Back 232

It has a “spoke” or “star-like” appearance around structures at the edges of the image. Structures at the center of the image are not affected.

Front 233

What is the limit to the number of slices collected in a single rotation is you are going to be using filtered back projection to reconstruct the images?

Back 233

Four Slices

Front 234

If your scanner is going to be collecting more than four slices per rotation (greater than 20mm) what type of reconstruction method will be used?

Back 234

Cone Beam Reconstruction

Front 235

T/F: Cone beam reconstruction also applies a reconstruction filter in order to improve the edge definition of structures or to minimize the appearance of noise.

Back 235

True

Front 236

Is there any need for back projection during the reconstruction process for a localizer scan?

Back 236

No

Front 237

Where is the raw data retained?

Back 237

On the raw data storage device on the host computer

Front 238

What do we access in order to generate Retrospective Image Reconstructions?

Back 238

The patient’s raw data files

Front 239

T/F: A retrospective reconstruction requires the raw data.

Back 239

True

Front 240

T/F: On MDCT scanners, a retrospective reconstruction is commonly used to modify the reconstructed slice thickness.

Back 240

True

Front 241

Define Multi-Planar reconstruction.

Back 241

Multi-planar reconstruction is a post-processing technique performed on image data which produces new slices from a set of CT scans.

Front 242

Some of the more sophisticated multi-planar reconstruction programs even allow a/an_________ ___________ to be placed on the original set of images

Back 242

curved cut-line

Front 243

To make sure that the reconstructed MPR images are diagnostic, it is important that the original slices do what?

Back 243

Have no gaps between them.

Front 244

What do we call slices with no gaps between them?

Back 244

Contiguous

Front 245

What type of imaging technique should be used when post processing is required?

Back 245

Helical Imaging.

Front 246

Using ____________ ________ in the initial data set improves the quality of the reconstructed images.

Back 246

overlapped

Front 247

What does 3D SSD stand for?

Back 247

Three Dimensional Shaded Surface Display

Front 248

What is 3D SSD?

Back 248

Reconstructed images of the surfaces of anatomical structures

Front 249

What are 4 applications for 3D SSD/

Back 249

1. Orthopedics
2. Planning for craniofacial surgery
3. Planning for neurosurgery
4. Planning for radiation therapy

Front 250

How does the 3D SSD reconstruction program begin?

Back 250

By stacking the transverse slices to form a volume of anatomical data.

Front 251

What is a threshold value/setting?

Back 251

It is the value that we set in a 3D SSD rendering that is equal to the CT number of the tissue of which we want the surface rendering.

Front 252

T/F: In a 3D SSD, only the tissues selected according to their threshold values will be displayed. All other CT numbers and their corresponding tissues will be ignored.

Back 252

True

Front 253

T/F: The reconstruction process is equally successful at extracting bony surfaces and skin as it is at distinguishing fat, muscle, and other soft tissues.

Back 253

False: The reconstruction process is usually much more successful at extracting bony surfaces and skin surfaces than at distinguishing fat, muscle, and other soft tissues whose CT numbers are much closer together.

Front 254

What reconstruction option reconstructs the inside of surfaces of pathways such as the bowel, bronchi and the sinuses?

Back 254

Virtual Endoscopy (a form of 3D SSD)

Front 255

In which type of 3D rendering is each voxel in the data set assigned an opacity value as a function of its density?

Back 255

Volume Rendering (VR)

Front 256

Volume rendering can incorporate information from the entire _______ _______ set. rather than just a/an ________, into the post-processed images, enabling visualization of structures _________ ____ _________ ____ _________.

Back 256

image data, surface, above and below the surface

Front 257

Each ______ of a volume rendered image represents the sum of the contributions of each _______ along a ____ passed through the image data set.

Back 257

pixel, voxel, ray

Front 258

What is the major drawback to volume rendering?

Back 258

The large computational requirements

Front 259

T/F: with advances in computers, computational requirements are nolonger a significant drawback and for many applications, volume renderings the preferred method of display.

Back 259

True

Front 260

What does MIP stand for?

Back 260

Maximum Intensity Projection

Front 261

MIP is most typically used for ____________________ (as well as _____________ studies).

Back 261

CT angiography, MR angiography

Front 262

How are MIP images generated?

Back 262

MIP images are generated from the transverse slices of a CTA study by projecting the brightest pixels onto a plane.

Front 263

Maximum intensity projection images are generated by projecting the highest _____ values from a _____ of CTA axial images along many ____ onto a single ______.

Back 263

pixels, stack, “rays”, image

Front 264

T/F: MIP images are most useful when depicting relatively simple anatomy in which there is little superimposition of structures.

Back 264

True

Front 265

In regards to MIP images, the lack of 3D information can be partially offset by doing what?

Back 265

By generating multiple MIP images at different angles about an axis of rotation and then displaying them as a movie, or cine loop.

Front 266

T/F: The MIP technique may require extensive editing to remove dense anatomic structures (bones), which would otherwise obscure the vessels of interest.

Back 266

True

Front 267

When are the most accurate MIP results obtained?

Back 267

When a small volume of interest is selected

Front 268

In regards to an MIP image, in a vascular dissection in which the true and false lumens are enhanced to the same degree, the membranes will only be visualized where they are oriented directly ________ to the viewing direction.

Back 268

parallel

Front 269

What does VOI stand for?

Back 269

Volume of Interest

Front 270

As the VOI from the helical image data included in the MIP increases, the apparent _________ __________ on the MIP image may decrease. This effect is most pronounced with ______ vessels and may even simulate _________________.

Back 270

vessel diameter, small, vessel occlusion

Front 271

T/F: Vascular depiction is most accurate with a narrow VOI.

Back 271

True

Front 272

Why is vascular depiction most accurate with a narrow VOI?

Back 272

Because using a narrow VOI reduces the inclusion of extraneous high intensity background pixels and increases the conspicuity of vascular structures.

Front 273

Unlike conventional radiography, CT uses a ______ __________ film.

Back 273

single emulsion

Front 274

Window adjustments allow us to concentrate on either ______ _________ detail or ______ _________ contrast by varying _____________ and ____________ settings.

Back 274

high resolution, soft tissue, brightness and contrast

Front 275

What are the two types of printers used to print CT images?

Back 275

1. Multi-Format Camera
2. Laser Camera

Front 276

What type of printer requires a photographic focusing lens?

Back 276

A multi-format camera printer

Front 277

T/F: Laser cameras do not require a photographic focusing lens.

Back 277

True

Front 278

Which is better, a laser camera printer or a multi-format camera printer and why?

Back 278

The Laser Camera Printer is better because the laser camera creates less scattered light which produces superior, high-contrast images compared with multi-format cameras.

Front 279

What is an important consideration when printing CT images, especially when they are the images to be interpreted by a Doctor/Radiologist?

Back 279

We must ensure that the image printed on the film looks identical to the one displayed on the monitor.

Front 280

When should increasing the dose to the patient be considered?

Back 280

Only when the result of no doing so would otherwise be a non-diagnostic study.

Front 281

List the three image quality factors.

Back 281

1. Contrast
2. Resolution
3. Noise

Front 282

Define Patient Dose.

Back 282

The dose is the amount of ionizing radiation absorbed by the patient per unit mass.

Front 283

There is a tradeoff between __________ the image quality and ___________ the patient dose.

Back 283

maximizing, minimizing

Front 284

What parameters affect patient dose?

Back 284

• Scan rotation time
• The tube current,
• The peak tube voltage
• The slice thickness
• The table increment
• The pitch
• The anatomical coverage desired

Front 285

The amount of attenuation is dependent upon What four factors?

Back 285

1. Atomic number
2. Density of electrons
3. Thickness
4. Photon energy

Front 286

Define Attenuation.

Back 286

Attenuation is the progressive reduction of the intensity of the x-ray beam as it passes through the patient’s tissues.

Front 287

X-ray photons are attenuated via what two processes?

Back 287

1. Absorption
2. Scattering

Front 288

The number of photons measured by the detectors is reduced in an ______________ fashion as the thickness of the tissue traversed is increased.

Back 288

exponential

Front 289

T/F: The attenuation of on x-ray beam is highly dependent upon the energy of the x-ray photons.

Back 289

True

Front 290

How long are a patients archives normally held for?

Back 290

One to seven years, depending on the state.

Front 291

CT scanners have many user-selectable parameters which can dramatically affect clinical _________ __________, __________ _______ and ______.

Back 291

image quality, patient dose and throughput

Front 292

What are the four influences on parameter selection?

Back 292

1. Contrast Resolution
2. Spatial Resolution
3. Image Noise
4. Patient Dose

Front 293

Define Contrast Resolution.

Back 293

Contrast Resolution is the ability to differentiate small differences in density on the image.

Front 294

Typically, tissues with differences in density of less than ______% can be differentiated with CT.

Back 294

0.5%

Front 295

What is the required difference in density in order for tissues to be differentiated with conventional radiography?

Back 295

10%

Front 296

Define Spatial Resolution.

Back 296

Spatial Resolution is a measure of the size of the smallest object that can be visualized, or resolved, in an image.

Front 297

What are the geometric factors of the scanner that affect spatial resolution?

Back 297

• Focal spot size
• Detector aperture size
• Focal spot to patient distance
• Patient to detector distance

Front 298

What are some of the parameters that we directly control that affect spatial resolution?

Back 298

• Slice thickness
• Display FOV
• Image Matrix
• The Reconstruction Filter

Front 299

How is spatial resolution measured?

Back 299

In line pairs per cm

Front 300

In a spatial resolution test for CT, what is one hole and one space referred to as?

Back 300

A line pair

Front 301

What does a resolution test consist of?

Back 301

Scanning a water filled phantom and determining the smallest line pair that can be resolved.

Front 302

What is the formula for determining spatial resolution if the set of lines with 8 line pairs per centimeter can just be resolved??

Back 302

Spatial Resolution = ___________10mm____________16 lines (there are 2 lines per pair)
* Spatial Resolution = 0.625 *

Front 303

The black stripes in a CT Spatial Resolution Phantom represent the ______.

Back 303

Holes

Front 304

What appears in a CT image as a point-to-point fluctuation in the CT number within a uniform material?

Back 304

Noise

Front 305

What do we call it when a CT image looks grainy or speckled?

Back 305

Noise

Front 306

T/F: noise makes it difficult to see subtle contrast differences or fine details.

Back 306

True

Front 307

There is a __________ correlation between the apparent noise level and the _______ ___ __________ used in making the image.

Back 307

direct correlation, number of photons

Front 308

T/F: There are no parameters on the scanner that directly allow us to decrease the amount of noise.

Back 308

True

Front 309

T/F: Increasing the number of photons increases the appearance of noise in the CT image.

Back 309

False: Increasing the number of photons decreases the appearance of noise in the CT image.

Front 310

What is the easiest way to increase the number of photons?

Back 310

Increase the tube current or the scan time.

Front 311

What would we call an x-ray beam composed of photons all having the same energy level?

Back 311

Monochromatic

Front 312

In reality, the x-ray photons generated by a CT x-ray tube have a variety of energies. This is referred to as being what?

Back 312

Polychromatic

Front 313

When an x-ray beam enters tissue and looses lower energy photons to attenuation, there is am increase in the mean energy of the beam. This is referred to as what?

Back 313

Beam Hardening

Front 314

The CT number scale is established relative to the attenuation of what?

Back 314

Water

Front 315

The CT number scale is also referred to as what?

Back 315

The Hounsfield scale

Front 316

Who produced the first clinically useful CT scanner for brain imaging and when did he/she do it?

Back 316

Hounsfield, in 1967

Front 317

What is the CT Number / Hounsfield Unit for water?

Back 317

0

Front 318

What is the CT Number / Hounsfield Unit for air?

Back 318

-1000

Front 319

What is the CT Number / Hounsfield Unit for fat?

Back 319

Approximately -80

Front 320

What is the CT Number / Hounsfield Unit range for soft tissue?

Back 320

Approximately 30 to 80

Front 321

Any measurements above _______ units generally indicates the presence of calcification.

Back 321

100

Front 322

Approximately what range does Congealed blood fall into?

Back 322

56 to 76 HU

Front 323

Approximately where does blood fall on the CT Number / Hounsfield scale?

Back 323

12 HU

Front 324

Each pixel in the image is assigned a ________ ________ __________ according to the CT number calculated by the___________ _________ ______________.

Back 324

gray scale number, filtered back projection

Front 325

Higher CT numbers (i.e., dense structures) are assigned __________ shades of gray and lower CT numbers (i.e., structures which are not dense) are assigned ________ shades of gray.

Back 325

lighter, darker

Front 326

The ______ is the tube current. The _______ is the product of tube current and time.

Back 326

mA, mAs

Front 327

T/F: The mAs does not affect the image contrast or resolution.

Back 327

True

Front 328

What do we call the time required for the tube and detectors to rotate a complete 360˚?

Back 328

The Rotation Time

Front 329

What is the factor that is responsible for the amount of noise we see in the image?

Back 329

The mAs

Front 330

What do we call the voltage that is applied across tha anode and the cathode?

Back 330

The Tube Voltage

Front 331

Changing the kVp of the scan involves a tradeoff between _________, ______ and apparent _________.

Back 331

contrast, dose and apparent noise

Front 332

T/F: kVp affects both the dose to the patient and the image noise.

Back 332

True

Front 333

T/F: In the range of energy levels used in CT, an increase in the kVp leads to a slight decrease in the radiation dose.

Back 333

False: It leads to a slight increase in the radiation dose.

Front 334

What is the only reason a technologist might consider changing the kVp for a given exam?

Back 334

If the patient is very large or very small

Front 335

What are the two factors that determine slice thickness on a single-row detector scanner?

Back 335

1. Focal Spot Size
2. Pre-Patient Collimation

Front 336

On single-row detector scanners, the collimated x-ray beam thickness equals the ____________ _______ ____________, which also equals the final ________ ___________.

Back 336

acquired slice thickness, image thickness

Front 337

On a single row detector scanner, the slice thickness is determined by the _______________ of the ___________.

Back 337

collimation of the x-ray beam

Front 338

What are the two slice thickness parameters that must be specified on a MDCT scanner?

Back 338

1. Acquired Slice Thickness
2. Reconstructed Slice Thickness or Effective Slice Thickness

Front 339

What is another name for Reconstructed Slice Thickness?

Back 339

Effective Slick Thickness

Front 340

The______________________ indicates which rows of detectors are being used to measure the photons that pass completely threw the patients body.

Back 340

Acquired Slice Thickness

Front 341

T/F: A thinner acquired slice thickness means that smaller detectors are being selected.

Back 341

True

Front 342

What do we call the thickness of the final image?

Back 342

The Reconstructed or Effective Slice Thickness

Front 343

T/F: On a MDCT Scanner, the reconstructed or effective slice thickness must be equal or greater than the acquired slice thickness.

Back 343

True

Front 344

What things are affected by slice thickness?

Back 344

1. Anatomical Coverage
2. Image Noise
3. Resolution along the direction perpendicular to the acquired images
4. Patient Dose

Front 345

How does the slice thickness affect noise?

Back 345

The pre-patient collimation allows more photons to reach the detectors when a thick slice is selected that when a thin slice is selected. So a thicker slice appears less noisy because there are more photons detected relative to the noise level in the thicker slice.

Front 346

The use of thicker slices reduces the resolution along the direction perpendicular to the _____________ direction.

Back 346

Z-direction

Front 347

The use of thick slices produces an effect called ____________ _____________ or _____________ __________ ____________.

Back 347

partial voluming, partial volume averaging.

Front 348

What do we call the effect that results from the from the mathematical averaging of several millimeters of varying density tissues, which is displayed as a single shade of gray on the resulting image?

Back 348

Partial Voluming

Front 349

T/F: as the slick thickness increases, the for the exam as a whole decreases.

Back 349

True

Front 350

The slice thickness must be chosen carefully to maintain an acceptable _______ _________ and appropriate _____________ while minimizing __________ __________.

Back 350

noise level, coverage, partial voluming

Front 351

By using thicker slices to cover the same anatomy, the radiation dose to the patient may be _____________.

Back 351

decreased

Front 352

On conventional or serial scans, the ________________ determines if the slices will be contiguous or if there will be a ______ or __________.

Back 352

table increment, gap or overlap

Front 353

To get contiguous slices, the table increment must be ________ to the slice thickness.

Back 353

equal

Front 354

T/F: Overlapping slices may provide more thorough coverage of the anatomy than contiguous slices.

Back 354

True

Front 355

What usually determines the amount of table incrementation selected?

Back 355

The amount of table incrementation selected usually depends on the size of the structures that need to be visualized in the clinical study.

Front 356

The anatomical coverage of a helical scan is determined by an important scan parameter called what?

Back 356

Pitch

Front 357

What is the definition of pitch on a single-row detector scanner?

Back 357

The pitch equals the movement of the patient table in one gantry rotation divided by the slice thickness.
or
Pitch = Movement of the patient table in one gantry rotation Slice Thickness

Front 358

The pitch determines how _________ the x-ray path is during a helical scan.

Back 358

stretched

Front 359

On a single-row detector scanner, a pitch of 1 means what?

Back 359

It means that the patient table moves a distance equal to the slice thickness during one rotation of the tube/detector assembly

Front 360

T/F: Different manufacturers use one of two different formulas for determining the pitch of their scanners.

Back 360

True

Front 361

List the two possible formulas for determining pitch (scanner dependant)

Back 361

Pitch = Movement of the patient table in one gantry rotation OVER
Total slice volume

Pitch = Movement of the patient table in one gantry rotation OVER
Thickness of a single slice

Front 362

On a multi-row detector scanner in which four slices are collected simultaneously, an un-stretched, contiguous helix would correspond to what pitch?

Back 362

Either 4 or 1

Front 363

List four reasons to increase the pitch.

Back 363

1. Greater anatomical coverage in less time
2. Faster scan for trauma
3. For appropriate contrast timing during a CTA study
4. Decrease the dose to the patient

Front 364

If the pitch is increased to more than 2 (i.e., in one rotation the patient table moves more than twice the total slice volume) ____________ artifacts will occur.

Back 364

helical

Front 365

What do helical artifacts look like?

Back 365

Helical artifacts look like swirls or windmills on the image.

Front 366

On single-row detector scanners, as the pitch is increased, there is an unfortunate increase in the ___________ ________ _____________.

Back 366

effective slice thickness

Front 367

What are two reasons that we might use a reduced pitch?

Back 367

1. Improving the resolution along the slice direction
2. Minimizing the appearance of noise in the image.

Front 368

What four things does pitch affect?

Back 368

1. Anatomical Coverage
2. Scan time
3. Resolution
4. Dose

Front 369

T/F: The pitch affects the amount of gap or overlap between slices.

Back 369

False: The pitch does not affect the amount of gap or overlap between slices! The pitch indicates how the data is going to be collected and the reconstruction interval handles the location of the reconstructed slices.

Front 370

T/F: “Reconstruction Interval” is a scan parameter that is specific to helical scans only.

Back 370

True

Front 371

Reconstruction interval refers to how the helical slices are what?

Back 371

Reconstructed

Front 372

In a helical scan, what determines weather the slices will be contiguous or if there will be a gap or an overlap of slices (images)?

Back 372

The Reconstruction Interval

Front 373

If the reconstructed interval is equal to the slice thickness, te reconstructed slice will be _______________.

Back 373

contiguous

Front 374

If the reconstruction interval is less than the slice thickness, the reconstructed slices will _____________.

Back 374

overlap

Front 375

T/F: A finer reconstruction interval may be used for helical data than would be practical with conventional overlapping slices.

Back 375

True

Front 376

What do we call a single picture element of the image matrix?

Back 376

A Pixel

Front 377

What do we call a volume element?

Back 377

A Voxel

Front 378

The pixels in a image represent the _____________ of a volume of tissue called a __________.

Back 378

CT number, voxel

Front 379

What defines the two dimensions of a voxel?

Back 379

1. Slice thickness
2. In-Plane Spatial Resolution

Front 380

What are the two types of FOVs?

Back 380

1. Scan Field Of View (SFOV)
2. Reconstruction or Display Field Of View (RFOV or DFOV)

Front 381

What determines the total area over which projection data is collected?

Back 381

The Scan Field Of View (SFOV)

Front 382

What determines the number of detectors collecting data for a particular scan?

Back 382

The SFOV

Front 383

How large should the SFOV be and Why?

Back 383

The SFOV should be large enough to cover all of the patient anatomy. If any part of the patient lies outside the SFOV, out-of-field artifacts will occur.

Front 384

Define Out-Of-Field artifacts.

Back 384

Out-Of-Field artifacts are characterized by image shading, streaks and incorrect assignment of CT numbers to the image pixels.

Front 385

Why must care be taken in choosing the scan FOV?

Back 385

Because correction and calibration algorithms are often affected when selecting a scan FOV. For example: Choosing a head scan FOV of 25 cm is not equivalent to choosing a small body scan FOV of 25 cm, and will not produce identical image quality.

Front 386

Define Reconstruction Field Of View (RFOV)

Back 386

RFOV is the region of interest illustrated in the resulting images and the FOV reconstructed from the complete set or raw data.

Front 387

T/F: The reconstruction or display FOV is always equal to or smaller than the scan FOV.

Back 387

True

Front 388

What does the Reconstruction or Display FOV affect?

Back 388

• The apparent zoom level in the image
• The appearance of noise
• The in-plane resolution of the image

Front 389

Minimizing the noise with a large reconstruction FOV is attained only by compromising the image’s __________________________.

Back 389

Spatial Resolution

Front 390

What is the In-Plane Spatial Resolution Formula?

Back 390

In-Plane Spatial Resolution = Reconstruction (Display) FOV
OVER
# of pixels along each direction in the matrix

or
Spatial Resolution =__DFOV___
OVER
The Matrix

Front 391

In all actuality, what does the in-plane spatial resolution formula determine?

Back 391

It determines the size of an object that can be seen in the resulting image.

Front 392

How do we optimize in in-plane spatial resolution?

Back 392

By using a small reconstruction FOV

Front 393

What are some limiting factors to the in-plane spatial resolution?

Back 393

• Focal Spot Size
• CT Scanner Geometry
• Detector Size
• Reconstruction Algorithm

Front 394

T/F: The image matrix does not affect the apparent noise or resolution of the resulting image.

Back 394

False

Front 395

T/F: A large matrix increases the appearance of image noise.

Back 395

True

Front 396

What is the most commonly used matrix size and is this value typically varied?

Back 396

512 x 512; No, it is not typically varied.

Front 397

T/F: Magnification does not affect the spatial resolution or affect the appearance of image noise.

Back 397

True

Front 398

What are you doing when you magnify an image?

Back 398

You are simply enlarging the individual pixels of the reconstructed image for display purposes.

Front 399

Why is spatial resolution and noise not affected by magnification?

Back 399

Because the same amount of anatomy is represented by each pixel.

Front 400

What is the only way to enlarge the size of the image if the raw data is no longer available?

Back 400

Magnification

Front 401

How many shades of grey can an operators console display?

Back 401

256

Front 402

How many shades of grey can the human eye distinguish?

Back 402

About 20 shades of grey

Front 403

How do we accommodate the limitations of only being able to display 256 shades of grey and only being able to see about 20?

Back 403

Window Width (WW) and Window Level (WL)

Front 404

What controls how “contrasty” the image appears?

Back 404

The Window Width

Front 405

Define Window Width.

Back 405

Window width refers to the range of CT numbers displayed on an image and it adjusts how “contrasty” the image appears.

Front 406

What pixel level (color) is assigned to any CT numbers above the range specified by the window width?

Back 406

255 (white)

Front 407

What pixel level (color) is assigned to any CT numbers below the range specified by the window width?

Back 407

0 (black)

Front 408

T/F: within the range determined by window width, the CT numbers are equally distributed from black to white.

Back 408

True

Front 409

How will increasing the window width change the representation of tissues on the image?

Back 409

It will represent a wider range of tissues on the image.

Front 410

When is a wide window width generally used?

Back 410

When viewing structures with a high degree of contrast, such as in the lungs. (Stark differences in density of tissues)

Front 411

How many shades of grey can an operators console display?

Back 411

256

Front 412

How many shades of grey can an operators console display?

Back 412

256

Front 413

How many shades of grey can the human eye distinguish?

Back 413

About 20 shades of grey

Front 414

How many shades of grey can the human eye distinguish?

Back 414

About 20 shades of grey

Front 415

How do we accommodate the limitations of only being able to display 256 shades of grey and only being able to see about 20?

Back 415

Window Width (WW) and Window Level (WL)

Front 416

How do we accommodate the limitations of only being able to display 256 shades of grey and only being able to see about 20?

Back 416

Window Width (WW) and Window Level (WL)

Front 417

What controls how “contrasty” the image appears?

Back 417

The Window Width

Front 418

What controls how “contrasty” the image appears?

Back 418

The Window Width

Front 419

Define Window Width.

Back 419

Window width refers to the range of CT numbers displayed on an image and it adjusts how “contrasty” the image appears.

Front 420

Define Window Width.

Back 420

Window width refers to the range of CT numbers displayed on an image and it adjusts how “contrasty” the image appears.

Front 421

What pixel level (color) is assigned to any CT numbers above the range specified by the window width?

Back 421

255 (white)

Front 422

What pixel level (color) is assigned to any CT numbers above the range specified by the window width?

Back 422

255 (white)

Front 423

What pixel level (color) is assigned to any CT numbers below the range specified by the window width?

Back 423

0 (black)

Front 424

What pixel level (color) is assigned to any CT numbers below the range specified by the window width?

Back 424

0 (black)

Front 425

T/F: within the range determined by window width, the CT numbers are equally distributed from black to white.

Back 425

True

Front 426

T/F: within the range determined by window width, the CT numbers are equally distributed from black to white.

Back 426

True

Front 427

How will increasing the window width change the representation of tissues on the image?

Back 427

It will represent a wider range of tissues on the image.

Front 428

How will increasing the window width change the representation of tissues on the image?

Back 428

It will represent a wider range of tissues on the image.

Front 429

When is a wide window width generally used?

Back 429

When viewing structures with a high degree of contrast, such as in the lungs. (Stark differences in density of tissues)

Front 430

When is a wide window width generally used?

Back 430

When viewing structures with a high degree of contrast, such as in the lungs. (Stark differences in density of tissues)

Front 431

When is a narrow window width useful?

Back 431

When visualizing structures exhibiting subtle inherent contrast, such as with the soft tissues of the brain. (Similar differences in density)

Front 432

What does the window level control?

Back 432

The brightness of the image. Specifically, the window level sets the center CT number displayed on the monitor.

Front 433

T/F: in general, the window level is set equal to the CT number of the tissue of interest.

Back 433

True

Front 434

Define Quality Assurance

Back 434

The procedure of performing specified tests or measurements on a periodic basis in order to assure that a set level of quality, as specified by the system manufacturer, has not been compromised.

Front 435

What are the two most frequently used standards for daily quality assurance assessment

Back 435

1. CT Number Calibration Test
2. CT Number Standard Deviation Test

Front 436

What are the two parameters evaluated during the CT number calibration test/CT number standard deviation test?

Back 436

The average value of the CT numbers and the standard deviation of the CT numbers within a region of interest.

Front 437

What are the acceptable limits for the CT Number Calibration Test?

Back 437

-3 to +3

Front 438

What is the -3 to +3 acceptable limit for the CT Calibration Test referring to?

Back 438

It refers to the fact that the CT number of water should be 0 (zero) but a variation of anywhere from -3 to +3 is acceptable.

Front 439

What are the acceptable limits for CT Number Standard Deviation?

Back 439

The Standard Deviation of water must not exceed a level specified by the manufacturer.

Front 440

What does an unacceptable Standard Deviation test indicate?

Back 440

It is an indication of an increase in the image noise which could be caused by either a decrease in the delivered dose, resulting in a lower than expected signal, or an increase in image noise in the detector-amplifier chain.

Front 441

What are some other tests performed on a less frequent basis by the service representative or site physicist? (11 items)

Back 441

• Spatial Resolution
• Contrast Resolution
• Table Accuracy
• Dose
• Accuracy of spatial measurements on the image
• Consistency of CT numbers across the image
• Linearity of the gray scale of the image as it relates to the actual density of tissues measured
• Radiation scatter and leakage
• Slice thickness accuracy
• Fidelity of the video monitor
• Film output

Front 442

The ARRT Standard of Ethics is comprised of what?

Back 442

The Code of Ethics and the Rules of Ethics.

Front 443

T/F: The ARRT does not review, evaluate, or endorse publications.

Back 443

True

Front 444

The ARRT Standard of ethics is ____________.

Back 444

aspirational

Front 445

T/F: Interpretation and diagnosis are outside the scope of practice for the profession.

Back 445

True

Front 446

The ARRT Code of Ethics offers __________ for ethical conduct.

Back 446

suggestions

Front 447

The ARRT Rules of Ethics are __________ policies that are _________, if ___________.

Back 447

enforceable, punishable, if violated

Front 448

Why were the ARRT Rules of Ethics created?

Back 448

To safeguard the patients comfort and safety

Front 449

Violating the ARRT Rules of Ethics is subject to ___________.

Back 449

sanctions

Front 450

What are the three goals of the Patients Bill of Rights and Responsibilities?

Back 450

1. To strengthen consumer confidence that the health care system is fair and responsive to consumer needs
2. To reaffirm the importance of a strong relationship between patients and their health care providers
3. To reaffirm the critical role consumers play in safeguarding their own health

Front 451

What are the 7 sets of patient rights?

Back 451

1. The right to Information
2. The right to Choose
3. Access to Emergency Services
4. Being a Full Partner in Health Care Decisions
5. Care Without Discrimination
6. The Right to Privacy
7. The Right to Speedy Complaint Resolution

Front 452

What is the one responsibility of the patient?

Back 452

Patients must take greater responsibility for maintaining good health.

Front 453

What do we call the State laws that have been developed to govern communication between health care providers and patients?

Back 453

Informed Consent Laws

Front 454

What determines weather consent may be given verbally or if it must be given in writing?

Back 454

The individual State Laws

Front 455

T/F: In some states, for procedures that entail greater risks, informed consent may only be obtained by a physician.

Back 455

True

Front 456

When is the only time that a patient’s consent may be presumed rather than obtained?

Back 456

In an emergency situation.

Front 457

What does PHI stand for in regards to HIPAA.

Back 457

Protected Health Information

Front 458

T/F: PHI may legally be used for activities such as teaching, business and management operations, disclosures required by law, and public health and other governmental reporting.

Back 458

True

Front 459

T/F: As a Technologist you must be a patient advocate first and an assistant to the physician second.

Back 459

True

Front 460

Define Malpractice.

Back 460

Malpractice is the failure to do something that a reasonable person, guided by those considerations which ordinarily regulate human affairs, would do.

Front 461

Define Negligence.

Back 461

Negligence is a breach or failure to fulfill the expected standard of care.

Front 462

What must be demonstrated in a lawsuit in order to prove negligence?

Back 462

1. Duty
2. Breach of Duty
3. Injury
4. Cause of Injury

Front 463

T/F: As a Technologist, you are responsible for your own negligent acts, regardless if another medical professional advises you to act in the negligent fashion.

Back 463

True

Front 464

List 4 key screening issues.

Back 464

1. The reason for the exam
2. The potential for pregnancy
3. The patient’s medical history
4. The values of lab tests

Front 465

T/F: If there is a discrepancy between the study ordered on the paperwork and the one described by the patient, further clarification must be sought.

Back 465

True

Front 466

By asking extensive questions about the patient’s medical history there are actually two pieces of information we are trying to learn. What are they?

Back 466

1. Does the patient have any conditions or tendencies to be intolerant to a contrast agent?
2. Does the patient have any history of prior surgeries or treatments we would expect to cause the CT images of this patient to differ from normal anatomy?

Front 467

Why might it be important to ask the patient if they have had had radiation therapy?

Back 467

Because scarring caused by radiation therapy mimics lung disease.

Front 468

What questions should be asked during screening for contrast agents?

Back 468

1. Previous reaction to contrast?
2. Allergies to iodine or barium?
3. Conditions such as hypertension, heart disease, asthma, sickle cell anemia, renal impairment or diabetes?

Front 469

What are the two types of lab results important to CT?

Back 469

1. Tests to determine renal function
2. Tests to determine the bloods ability to coagulate

Front 470

What are the two tests that determine renal function?

Back 470

BUN and Creatinine

Front 471

What does BUN provide?

Back 471

It provides information about the kidney’s ability to remove impurities from the blood.

Front 472

What does an elevated BUN indicate the possibility of?

Back 472

Renal Disease

Front 473

What is the normal/ acceptable range for BUN values?

Back 473

5 to 25 mg/dl

Front 474

Why can an elevated creatinine level be a contraindication for IV contrast?

Back 474

Creatinine is a waste product of muscle contraction that is normally filtered out of the body by the kidneys. Elevated creatinine levels may indicate impairment of the function of the kidneys.

Front 475

What is the normal range for creatinine?

Back 475

6 to 1.7 mg/dl

Front 476

What are the three tests that determine the bloods ability to coagulate?

Back 476

1. Prothrombin Time (PT)
2. Partial Thromboplastin Time (PTT)
3. Platelet Count

Front 477

T/F: Platelets are small cell fragments that do not contain a nucleus.

Back 477

True

Front 478

What two tests asses the series of chemical interactions required to form a blood clot?

Back 478

PT and PTT

Front 479

What are the typically accepted values for PT, PTT and Platelet count?

Back 479

PT = 10 to 14 seconds
PTT = 20 to 40 seconds
Platelet Count = 150,000/mm³ to 400,000/mm³

Front 480

What are the two ways that x-rays which penetrate the tissues can cause damage to the body?

Back 480

1. By breaking electron bonds and forming ion pairs (Indirect Effect) (more likely)
2. By directly disrupting the DNA bonds within the nuclei of cells in the patient’s body (Direct Effect)(less likely)

Front 481

As a result of radiation exposure during pregnancy, there is an increased incidence of what?

Back 481

• Prenatal deaths
• Abnormalities
• Mental Retardation
• Neonatal Deaths due to complications

Front 482

When dealing with strictly x-rays, what is the most common unit for measuring absorbed radiation dosage?

Back 482

The rad

Front 483

How much radiation is in 1 rad?

Back 483

1 rad = 0.01 joules of energy per kilogram of matter (the patients weight)

Front 484

Radiation strictly from x-rays is measured in _____ or ______. Sv and rem are used to measure ________________ radiation.

Back 484

rad or Gy (Gray), any kind of

Front 485

Rem and Sievert are a measurement of what?

Back 485

Effective Dose” or “Dose Equivalent”

Front 486

What is the average annual radiation dose equivalent from radon?

Back 486

2 rem

Front 487

The _________ the distance traveled through the tissue and the ________ the tissue the x-ray photons penetrate, the more the dose is decreased along the photons’ path.

Back 487

greater, denser

Front 488

What are the typical skin radiation doses for CT scans of the head, body and the localizer scan?

Back 488

Head Scan 1-5 rads
Body Scan 2-6 rads
Localizer Scan 0.05-0.1 rads

Front 489

What is the approximate Skin Dose and Center Dose for a 30 slice CT study?

Back 489

Skin Dose 5 rad
Center Dose 1 rad

Front 490

What is the approximate Skin Dose and Center Dose for 1 radiography film?

Back 490

Skin Dose .5 rad
Center Dose 0.15 rad

Front 491

What is the approximate Skin Dose and Center Dose for 5 radiography films?

Back 491

Skin Dose 2.5 rad
Center Dose 0.75 rad

Front 492

What do we call radiation that extends outside of the intended slice?

Back 492

Radiation Penumbra

Front 493

How is the actual dose from multiple adjacent slices measured?

Back 493

By an important indicator of radiation dose called the CT dose index, or CTDI.

Front 494

The ___________ is an indicator of radiation dose which includes the radiation located within the intended slice thickness as well as that from the penumbra.

Back 494

The CT Dose Index or CTDI

Front 495

T/F: The CTDI does not factor in the variation in dose due to gaps or overlaps in adjacent slices.

Back 495

True

Front 496

The ________ assumes that consecutive slices are contiguous.

Back 496

CTDI

Front 497

In order to account for gaps or overlaps between adjacent slices there is another indicator of dose called the _________________________.

Back 497

Multiple Slice Average Dose or MSAD

Front 498

The MSAD is _________ than the CTDI when the slices or loops of the helix overlap and the MSAD is ___________ than the DTDI when there are gaps

Back 498

greater, lower

Front 499

T/F: The more slices collected by the MDCT scanner in a single rotation, the less the penumbra effect adds to the total patient dose.

Back 499

True

Front 500

There is no federally imposed limit to radiation exposure.

Back 500

True

Front 501

T/F: The further the CT Tube is situated from the patient, the lower the absorbed dose.

Back 501

True

Front 502

How does varying the collimation affect the dose for that slice?

Back 502

Collimation determines the radiation penumbra and it also affects scatter radiation.

Front 503

T/F: Collecting multiple slices at the same time on a MDCT scanner delivers more dose to the patient than does conventional or serial scanning.

Back 503

True

Front 504

Why was dose-optimized software developed?

Back 504

As a response to the realization that the newer scanners (MDCT) would otherwise increase the dose to the patient.

Front 505

What does the dose-optimized software do?

Back 505

It automatically adjusts the mA

Front 506

What are the four hardware factors affecting dose?

Back 506

1. X-ray tube to patient distance
2. Filtration
3. Pre-patient Collimation
4. Multi-row detector design along with dose minimizing software

Front 507

Manufacturers claim that their dose-optimizing software which automatically varies the mA allows for dose reductions ranging from ______ % to ______%.

Back 507

15% to 55%.

Front 508

What are some other features for minimizing the radiation dose to the patient found on new CT scanners?

Back 508

• “Noise Reduction Algorithms
• Improvements in the efficiency of the detectors

Front 509

There is a __________ relationship between mAs and dose.

Back 509

Linear

Front 510

T/F: kVp is usually only decreased to minimize dose in small patients.

Back 510

True

Front 511

Slice thickness really only affects the dose to the patient on MDCT scanners.

Back 511

False: Slice thickness really only affect the dose to the patient on single-row detector scanners.

Front 512

T/F: For MDCT scanners, the slice thickness always affects the dose.

Back 512

False: For MDCT scanners, the slice thickness does not affect the dose.

Front 513

What are some other ways to minimize dose?

Back 513

• Reduce repeat scans
• Reformat rather than re-scan
• Reduce multiple scans

Front 514

During the CT scan, the patient should be monitored both __________ and ____________.

Back 514

visually and verbally

Front 515

If a patient is sedated, what type of monitoring device is recommended?

Back 515

A Pulse Oximeter

Front 516

How do you identify Cardiac Arrest?

Back 516

• No Pulse
• No respiration
• Vomiting
• Seizure
• Damp bluish or grayish skin tone
• Incontinence or defecation

Front 517

What are some signs of a Seizure?

Back 517

• Uncontrollable muscular contractions
• Facial Twitching
• Blank facial expression
• Loss of motor activity
• Difficulty breathing
• Confusion

Front 518

What should you do if your patient is having a seizure?

Back 518

All restraints and objects that could cause harm should be removed and the patient should be eased into a resting position (e.g., on the patient table, a chair, or the floor).

Front 519

What results from a lack of blood flow to the brain?

Back 519

Stroke

Front 520

What are some signs of a stroke?

Back 520

• Inability to communicate
• bilateral or unilateral numbness or paralysis
• Pupil disparity
• Incontinence
• Hypertension

Front 521

What should be done when a patient has a stroke?

Back 521

• Monitor vital signs frequently
• Prepare patient for airway ventilation, suction, intravenous fluids and possible CPR

Front 522

What results from insufficient blood flow to the tissues and vital organs?

Back 522

Shock

Front 523

What can cause shock?

Back 523

• Loss of blood volume
• Sudden massive vasodilation

Front 524

What type of shock occurs from IV contrast injection?

Back 524

Anaphylactic shock (sudden massive vasodilation)

Front 525

What are some signs of shock?

Back 525

• Altered levels of consciousness
• Hypotension
• Cool bluish or grayish skin tone
• Tachycardia
• Restlessness

Front 526

What are the key vital signs and their normal values?
Temperature:

Back 526

Orally 97˚ F to 99˚ F
Axilla 96.5˚ F to 98.5˚ F
Rectal 97.5˚ F to 99.5˚ F

Front 527

What are the key vital signs and their normal values?
Pulse:

Back 527

Adult 70 to 100 BPM
Athletic 45 to 60 BPM
Child 95 to 110 BPM
Infant 100 to 180 BPM

Front 528

What are the key vital signs and their normal values?
Blood Pressure:

Back 528

Systolic Diastolic
Adult 90-140 60-90
Children 85-130 45-85

Front 529

What are the key vital signs and their normal values?
Respiratory rate:

Back 529

Respirations/minute
Adults 12-20
Children 15-30
Infants 25-50

Front 530

How should you treat a patient experiencing shock?

Back 530

They should be kept warm with legs elevated (provided there are no bleeding wounds in the upper body or head). If it is anaphylactic shock a medication such as epinephrine can be administered.

Front 531

How accurately should temperatures be recorded?

Back 531

To the nearest tenth of a degree

Front 532

What do we call the rules that all health care workers must follow in order to minimize the spread of infection?

Back 532

Standard or Universal Precautions

Front 533

When and why was the ecessity for universal precautions first identified?

Back 533

In the mid 1980s as a result of the HIV epidemic

Front 534

Give three examples of bloodborne pathogens.

Back 534

1. Hepatitis B
2. Hepatitis C
3. HIV

Front 535

In 1996 the definition and recommendations for Universal Precautions was revised and given a new name. What was that name?

Back 535

Standard Precautions

Front 536

What body substances does standard precautions apply to?

Back 536

• Blood
• Body Fluids
• Secretions
• Excretions (except sweat)
• Non-Intact Skin
• Mucous Membranes

Front 537

What are some of the more common standard precaution procedures?

Back 537

• Handwashing
• Gloves
• Mask, Eye Protection, Face Shield
• Gowns
• Sterilizing Equipment
• Linens
• Needles
• Patient placement

Front 538

What form of infection transmission occurs by dissemination of either airborne droplet nuclei (small-particle residue [5 um or smaller in size] of evaporated droplets that may remain suspended in the air for long periods of time) or dust particles containing the infectious agent?

Back 538

Airborne Transmission

Front 539

What do we call the precautions associated with airborne infection transmission?

Back 539

Airborne Precautions

Front 540

List the Airborne Precautions.

Back 540

• Negative air pressure in room (6 to 12 air changes per hour)
• Wear N95 respirator into room
• Place mask on patient if transport is necessary

Front 541

What type of infection transmission involves contact of the conjunctivae or the mucous membranes of the nose or mouth of a susceptible person with large-particle droplets (larger than 5 um in size) containing microorganisms generated from an infected person.

Back 541

Droplet Transmission

Front 542

What do we call the precautions used when dealing with droplet infection transmission?

Back 542

Droplet Precautions

Front 543

List the Droplet Precautions.

Back 543

• Maintain at least 3 feet between infected patients and other patients
• The door may remain open
• Wear a mask when working within 3 feet of the patient
• Mask patient during transport if possible

Front 544

How far can droplets travel?

Back 544

Up to 3 feet

Front 545

Which type of precautions are designed to reduce the risk of transmission of epidemiologically important microorganisms by direct contact?

Back 545

Contact Precautions

Front 546

List the Contact Precautions.

Back 546

• Gloves and Handwashing
• Wear a Gown
• Wear Gloves and gown during transport

Front 547

Contrast media is used to improve the ___________ and the ____________ of clinical diagnosis.

Back 547

sensitivity, specificity

Front 548

What are the four groups of contrast media?

Back 548

1. Intravenous (IV) Contrast Agents
2. Oral Contrast Agents
3. Intrathecal Contrast Agents
4. Intra-Articular Contrast Agents

Front 549

T/F: Oral contrast agents are sometimes administered rectally in order to reach the distal GI tract.

Back 549

True

Front 550

Other than barium and gastrographin, what are some other oral contrast agents?

Back 550

Air and water

Front 551

Intrathecal contrast agents are injected into the spinal ________________ space during a ______________ exam of the spine.

Back 551

subarachnoid, myelographic

Front 552

T/F: Intrathecal contrast is not normally administered in the CT department, but may be encountered there.

Back 552

True

Front 553

What factors come into play when deciding upon a particular contrast agent?

Back 553

• Patient Tolerance
• Patient History
• Method
• Rate of Administration
• Cost
• Radiologist preference

Front 554

What do all IV contrast agents have in common?

Back 554

They all contain iodine

Front 555

The iodine in the contrast media increases the ___________ of the x-ray photons.

Back 555

attenuation

Front 556

T/F: Contrast media helps delineate tissues and pathology.

Back 556

True

Front 557

Tissues perfused by IV contrast media appear ________ on CT images.

Back 557

brighter

Front 558

The increase in brightness on the CT image associated with tissues perfused by IV contrast agents is referred to as what?

Back 558

Enhancement

Front 559

_________ IV contrast agents divide into charged particles (called ions) when in a solution, like the patients blood stream.

Back 559

Ionic IV contrast agents

Front 560

_____________ IV contrast agents do not divide into charged particles when in solution (like the patient’s blood)

Back 560

Non-ionic

Front 561

When a ____________ agent is injected, the entire molecule remains intact as it passes through the body and is excreted in the same form by the kidneys.

Back 561

non-ionic

Front 562

T/F: The more an agent breaks down into a greater number of charged particles, the better it is tolerated.

Back 562

False: The LESS an agent breaks down into a greater number of charged particles, the better it is tolerated.

Front 563

Define Osmolality.

Back 563

Osmolality is the concentration of molecular particles in the contrast agent solution.

Front 564

Based on osmolality, contrast media can be divided into what two groups?

Back 564

1. Low Osmolar Contrast Media (LOCM)
2. High Osmolar Contrast Media (HOCM)

Front 565

Non-ionic contrast belongs to the ______ Osmolar category of IV contrast.

Back 565

low

Front 566

What is the concentration of particles in a non-ionic, low osmolar IV contrast agent?

Back 566

Around 500 to 850 mOsm/kg

Front 567

What is the concentration of particles in an ionic, high osmolar IV contrast agent?

Back 567

Around 1300 to 1600 mOsm/kg

Front 568

Generally speaking, agents have a greater osmolality than blood plasma.

Back 568

True

Front 569

IV contrast agents are said to be _______________ or ______________ compared to blood plasma.

Back 569

hyperosmolar or hypertonic

Front 570

_________________ (hypertonic / hypotonic) solutions will cause a net movement of water from within the tissues into the vascular space.

Back 570

hypertonic

Front 571

Why is it important for the patient to be well hydrated both before and after the administration of IV contrast?

Back 571

Because the hypertonic nature of the IV contrast agent can cause a net movement of water from within the tissues into the vascular space(dehydration).

Front 572

Define Viscosity.

Back 572

Viscosity is a measure of the “thickness” of a liquid, related to the frictional forces of the molecules of the substance as they flow past one another.

Front 573

T/F: the thicker, or more viscous the contrast media solution, the less force will be required to administer the solution into the patient.

Back 573

False: The more force will be required

Front 574

What would make a contrast agent have a high viscosity?

Back 574

If it’s molecules are large.

Front 575

T/F: The kidneys have a harder time clearing large particles from the blood than small particles.

Back 575

True

Front 576

About what percentage of patients injected with IV contrast will have some sort of reaction?

Back 576

About 6% to 8%

Front 577

What to we consider a minor reaction?

Back 577

Those that last briefly tend to cause the patient only minor discomfort and generally do not require any treatment.

Front 578

List eleven “minor” reactions to IV contrast agents.

Back 578

1. Nausea
2. Chills
3. Vomiting
4. Feeling of warmth
5. Minor hives
6. Unusual, metallic taste sensation
7. Itching
8. Shaking
9. Headache
10. Dizziness
11. Sweating

Front 579

What do we consider a moderate reaction?

Back 579

Those that are a bit more serious, which may require treatment and close observation, although hospitalization is typically not required.

Front 580

List six “moderate” reactions to IV contrast agents.

Back 580

1. Moderate hives
2. Change in pulse rate
3. Hypotension or hypertension
4. Wheezing
5. Bronchospasm or laryngospasm
6. Facial edema

Front 581

What are the two categories of reaction mechanisms?

Back 581

Chemotoxic and Idiosyncratic

Front 582

Define a Chemotoxic reaction.

Back 582

A Chemotoxic reaction mechanism is one that can be directly attributed to factors that include: physiological properties, the total volume of agent injected and the rate of injection.

Front 583

Define an Idiosyncratic reaction.

Back 583

An idiosyncratic reaction is one that is caused by anything besides the type, amount or rate of contrast injected.

Front 584

Due to __________, the patient’s blood vessels will dilate to compensate for the increased volume of fluid in the vessels during an IV contrast injection. This type of reaction mechanism would be referred to as what?

Back 584

osmosis, Chemotoxic Reaction Mechanism.

Front 585

What is believed to contribute to pain associated with vessel dilation, as well as flushing, changes to red blood cells, vascular endothelium damage, vomiting, nausea, and dehydration; and what type of reaction mechanism category would this fall under?

Back 585

The rapid movement of fluid, especially water, through the vascular system. This would fall under the Chemotoxic Reaction Mechanism category.

Front 586

How can the severity of the osmotic effect, and the associated reaction, be reduced?

Back 586

By administering non-ionic, low osmolar contrast media.

Front 587

T/F: A very viscous agent may contribute to discomfort at the injection site.

Back 587

True

Front 588

How can the viscosity of any contrast agent be reduced?

Back 588

By warming the agent to approximately body temperature.

Front 589

T/F: Increased injection rates are also associated with an increase in instances of adverse reactions.

Back 589

True

Front 590

T/F: Fear and stress resulting from the CT examination have also been known to trigger a histamine release.

Back 590

True

Front 591

_______________ acts by constricting smooth muscle and venules, dilating arterioles, producing localized edema, accelerating heart rate, lowering blood pressure, and increasing gastric and mucous secretions.

Back 591

Histamine

Front 592

What category of reaction mechanism can be caused by anything other than the properties of the contrast agent, the amount injected, or the injection rate?

Back 592

Idiosyncratic Reaction Mechanism

Front 593

What is believed to be responsible for reactions such as hypotension and hives?

Back 593

It is believed that when an excessive amount of histamine is released in the body, the vascular system becomes overloaded and histamine passes into the surrounding tissues and causes hypotension and hives.

Front 594

What might a facility do in order to prevent histamine reactions?

Back 594

Pre-medicate with an anti-histamine or steroids.

Front 595

What are some conditions that call for non-ionic contrast media?

Back 595

• Diabetes
• Functional diseases of the liver and kidneys

Front 596

How warm should IV contrast be before being injected into the patient?

Back 596

Approximately body temperature

Front 597

Anti-histamines or steroids may be administered to a patient prior to an IV contrast injection in order to try to prevent or lessen the severity of which type of reaction mechanism?

Back 597

Idiosyncratic Reaction Mechanism

Front 598

What are the two categories of lab tests that are required in some facilities before patients can receive IV contrast?

Back 598

1. Laboratory tests done to determine the kidneys’ ability to clear impurities from the vascular system
2. Tests done to asses the bloods ability to coagulate

Front 599

Why would you instruct the patient to be NPO for several hours before the CT study, with the exception of an oral contrast?

Back 599

• An empty stomach allows for better diagnostic evaluation
• Fasting reduces peristalsis which can cause motion artifacts
• An empty stomach is beneficial should the patient become nauseous or vomit after receiving the contrast agent

Front 600

What precautions are taken with diabetic patients?

Back 600

If the patient is taking Metformin (Glucophage) they should be instructed to refrain from taking it for 48 hours following the procedure. Then, Metformin should be resumed only after kidney function has been reassessed and determined to be normal.

Front 601

T/F: In patients with diabetes or renal insufficiency, a low osmolar, non-ionic contrast agent is safer for the kidneys.

Back 601

True

Front 602

What governs who can administer IV contrast?

Back 602

The rules governing who can administer IV contrast media vary from state to state.

Front 603

What should you do if you see particulate matter in the IV contrast?

Back 603

Read the label; it will tell you how to get rid of it or if the contrast needs to be discarded.

Front 604

What size catheter is generally used for IV contrast injection?

Back 604

18-22 Gauge

Front 605

What does PICC stand for?

Back 605

Peripherally Inserted Central Catheter

Front 606

What are the advantages of plastic-sheathed needle/ catheter combinations over butterfly-type needles?

Back 606

The needle/catheter combination allows for greater rates of injection and has a greater tendency of staying in the vein, minimizing the occurrence of extravasation or injection directly into the soft tissue.

Front 607

What is the routine IV contrast injection rate?

Back 607

2 to 3 cc/sec.

Front 608

What injection rate would you use for a CTA?

Back 608

4 to 5 cc/sec.

Front 609

When starting an IV, to get a better view of the vessels we have to work with, we need to __________ the vessels by applying a tourniquet.

Back 609

distend

Front 610

When should the veins on the dorsum of the hand be used?

Back 610

Only if there is a lack of venous access to the vessels at the elbow or cubital fossa.

Front 611

T/F: If the veins of the hand are used, a smaller catheter and slower injection rate than typically used will be required.

Back 611

True

Front 612

Which vein drains the dorsal part of the hand, and runs between the pectoralis major and the deltoid muscles, through the clavipectoral fascia and finally joins the axillary vein?

Back 612

The Cephalic Vein

Front 613

Why is the cephalic vein less desirable for insertion of the catheter/

Back 613

Because it’s tortuous route makes the flow more likely to be impeded when the patient’s arms are raised.

Front 614

Which vein is the vessel of choice for injecting IV contrast media?

Back 614

The Basilic Vein

Front 615

List four techniques for distending the veins.

Back 615

1. Apply tourniquet
2. Have patient pump hand
3. Slap vein
4. Apply heat

Front 616

What causes the basilic vein to remain more stationary than the cephalic vein when starting an IV in the cubital fossa?

Back 616

There is an anastomosis between the basilic and cephalic veins at the elbow which helps the basilic vein to remain quite stationary within the subcutaneous tissue.

Front 617

How much should the needle tip be withdrawn before advancing the catheter up the vein?

Back 617

2 to 3 millimeters

Front 618

What are the three phases of tissue enhancement?

Back 618

1. Bolus Phase
2. Non-equilibrium Phase
3. Equilibrium Phase

Front 619

The amount of time that each injection takes is directly related to the __________ _________, the _____________________________, and the ____________________.

Back 619

injection rate, volume of the injection, velocity of the blood flow

Front 620

What side of the heart receives blood returning to the heart threw the superior and inferior vena cava?

Back 620

The right side of the heart.

Front 621

When does the bolus phase of enhancement begin?

Back 621

Just after the contrast agent is injected.

Front 622

What defines the bolus phase of enhancement?

Back 622

There is a significant density difference between the abdominal aorta and the inferior vena cava.

Front 623

During which of contrast enhancement are CTA images of optimal quality?

Back 623

During the Bolus phase of contrast enhancement

Front 624

What characterizes the Non-equilibrium phase of contrast enhancement?

Back 624

There is a 10 to 30 HU density difference between the abdominal aorta and the inferior vena cava.

Front 625

During what phase of contrast enhancement does the bolus start to disburse into the capillaries, and then into the veins?

Back 625

The Non-Equilibrium Phase

Front 626

During which phase of contrast enhancement do we generally obtain the best differentiation of structures in the soft tissues as a result of contrast injection?

Back 626

The Non-Equilibrium Phase

Front 627

What characterizes the equilibrium phase of contrast enhancement?

Back 627

There is a density difference of less than 10 HU between the abdominal aorta and the inferior vena cava.

Front 628

During what phase of contrast enhancement is the agent’s concentration in the veins similar to the concentration in the arteries?

Back 628

During the equilibrium phase of contrast enhancement

Front 629

Why is the liver a unique organ?

Back 629

Because it is the only organ with a dual blood supply

Front 630

The liver receives about _____% of its blood from the portal vein and about _____% from the hepatic artery.

Back 630

80%, 20%

Front 631

When does the hepatic arterial phase of liver enhancement occur?

Back 631

20 to 40 seconds after the start of the injection.

Front 632

When does the portal venous phase of liver enhancement occur?

Back 632

60 to 90 seconds after the start of the injection.

Front 633

Most tumors are _________ (more/less) vascular than the liver itself and will be most obvious during the _________ ______ phase.

Back 633

less, portal venous

Front 634

A smaller set of hepatic tumors is ________ (more/less) vascular than the liver, however, and may only be visible during the ________ ________ phase.

Back 634

more, hepatic arterial

Front 635

Since the liver has a/an __________ blood supply, the ________ of the scan following the start of the injection is crucial.

Back 635

dual, timing

Front 636

If scanning is performed in the liver later than the portal venous phase, in the equilibrium phase, many hepatic tumors become ___________ with the liver tissue and may not be visible on the images.

Back 636

isodense

Front 637

A delayed scan of the brain after injection of IV contrast may be required in order to visualize what?

Back 637

• Multiple Sclerosis
• Metastatic lesions
• AIDS-related abnormalities

Front 638

A delayed scan of the pelvis after injection of IV contrast may be required in
order to visualize what?

Back 638

• Cancer of the prostate
• Cancer of the ovaries
• Cancer of the uterus

Front 639

What are two scanner determined factors that must be considered when calculating delay times?

Back 639

1. Is it going to be a serial scan or a helical scan? Serial scans take longer so scanning usually starts immediately after injection.
2. Is it a single-row detector scanner or a MDCT scanner? A MDCT scanner will cover the anatomy much faster than a single-row detector scanner.

Front 640

What could cause a patient to have a diminished cardiac output?

Back 640

• Shock
• Compromised blood flow

Front 641

What is a ‘Test Bolus”?

Back 641

A test bolus is used to determine how long it takes for a bolus of IV contrast media to reach the region of interest.

Front 642

What are the two methods used to determine the proper timing between the administration of contrast and the initiation of the CT scan?

Back 642

1. Automated Software
2. Test Bolus

Front 643

What are the benefits of oral contrast?

Back 643

• It helps reduce the risk of misdiagnosing fluid-filled bowel as an abscess or tumor
• It helps to visualize is a lesion is exterior to the bowl or whether it infiltrates the bowel

Front 644

What does oral contrast do besides just attenuating x-ray photons?

Back 644

It displaces air and fluid in the bowels.

Front 645

What are the two categories of Oral Contrast Media?

Back 645

1. Barium Sulfate
2. Iodinated

Front 646

List two types of negative contrast agents.

Back 646

Air and water

Front 647

What can be administered in order to inhibit gastric peristalsis?

Back 647

Glucagon

Front 648

Why might a patient swallow a final dose of water after consuming the barium or iodine solution?

Back 648

This keeps the gastric contents from being opacified and allows evaluation of the gastric wall.

Front 649

T/F: for virtual colonoscopy studies, we do not want to opacify the bowel with an agent.

Back 649

True

Front 650

What type of contrast is administered for a virtual colonoscopy study and how is it administered?

Back 650

A negative contrast agent such as air or CO2 is administered through the rectum in order to distend the bowel so that we can see the interior surfaces.

Front 651

Barium sulfate solutions used in CT are much more dilute than those used in conventional radiography, typically containing a _____ to ______% barium sulfate suspension.

Back 651

1 to 3%

Front 652

Barium sulfate is an _______, ___________ substance that is not __________ or ___________ in the body.

Back 652

inert, insoluble, absorbed or metabolized

Front 653

T/F: The density of a barium sulfate suspension is diminished as it passes through the GI tract.

Back 653

False

Front 654

T/F: Barium sulfate solutions are known for passing threw the GI tract slowly.

Back 654

True

Front 655

What can be done to help the barium sulfate solution to move through the GI system faster?

Back 655

Mix some faster-moving iodinated oral contrast media with the barium sulfate solution.

Front 656

Why are barium sulfate agents usually well tolerated by the body?

Back 656

Because they are not absorbed

Front 657

What are the most frequent adverse reactions to barium sulfate?

Back 657

• Diarrhea
• Abdominal Cramping
• Colon Impaction (rare)
• Barium Granuloma
• Barium Appendicitis
• Intestinal perforation
• Peritonitis

Front 658

What are some contraindications to using barium sulfate?

Back 658

• Colon obstruction
• Perforation
• Tracheosophageal fistula
• Obstructing lesions of the small intestine
• Pyloric stenosis
• Known hypersensitivity to barium sulfate

Front 659

Administration timing and dose of barium sulfate agents are largely dependent upon what?

Back 659

The area to be opacified

Front 660

T/F: Keeping the stomach free from oral contrast media enables better visualization of abnormalities on the stomach wall.

Back 660

True

Front 661

T/F: Iodinated oral agents are more concentrated than iodinated IV agents.

Back 661

False: They are less concentrated than iodinated IV agents

Front 662

What are the concentrations of iodinated oral agents?

Back 662

From 6 to 9 mg of iodine per ml

Front 663

Why are oral iodinated contrast agents tolerated so much better than IV iodinated contrast agents?

Back 663

Because oral agents use a much lower concentration of iodine

Front 664

When is iodinated oral contrast agent used?

Back 664

When barium sulfate agents are contraindicated

Front 665

How much of the Iodinated oral contrast is absorbed by the body?

Back 665

Around 0.1 to .5%

Front 666

T/F: If there is a risk of aspiration, iodinated oral agents are contraindicated.

Back 666

True

Front 667

Why is iodinated oral contrast contraindicated if there is a risk of aspiration/

Back 667

Aspiration of these agents can result in severe pulmonary edema

Front 668

What are some common reactions to iodinated oral contrast agents?

Back 668

• Transient diarrhea
• Abdominal pain
• Flatulence

Front 669

During a myelographic study, what space is the Intrathecal contrast injected into?

Back 669

The subarachnoid space.

Front 670

What are the procedures for a post-myelographic CT?

Back 670

• Elevate Head
• Confirm density of the contrast media
• Ensure that contrast media does not separate from the CSF

Front 671

Interaarticular contrast may be administered prior to CT evaluation of which joints?

Back 671

• Hip
• Knee
• Ankle
• Shoulder
• Elbow
• Wrist
• TMJ

Front 672

What sensations may be experienced by the patient during the injection of interaarticular contrast?

Back 672

Pressure, pain, tingling, or a feeling of fullness

Front 673

What structures normally enhance during administration of IV contrast for a CT of the head?

Back 673

• Blood vessels
• Choroid plexus
• The Dura

Front 674

Iodinated contrast agents do not cross an intact blood brain barrier.

Back 674

True

Front 675

What is a typical dose of IV contrast for a head scan?

Back 675

100ml

Front 676

Why do most lesions of the heat enhance?

Back 676

Due to a break in the normal blood brain barrier

Front 677

About how long would you wait before scanning the head after the injection of IV contrast for studies involving metastatic disease, AIDS or multiple sclerosis?

Back 677

About 45 minutes

Front 678

List 12 CT studies of the head that do not require the administration of IV contrast media.

Back 678

1. Sinusitis
2. Trauma
3. Grave’s disease
4. Early-stage cerebrovascular events
5. Early-stage subdural hematoma
6. Hydrocephalus
7. Dementia
8. Mastoiditis
9. Labyrinthitis
10. Facial or seventh nerve palsy
11. hearing loss
12. Studies of the petrous and temporal bones

Front 679

Why are IV contrast agents used in studies of the neck?

Back 679

Because they allow for the differentiation of blood vessels from lymph nodes and outline the epidural venous plexus

Front 680

Blood vessels and vascular tumors appear __________ (more/less) dense than lymph nodes when IV contrast media is used.

Back 680

more

Front 681

What is the typical dosage of IV contrast, injection rate and delay time for studies of the neck?

Back 681

100 to 125 ml @ 2 to 2.5 ml/sec, with a delay time of approximately 35 seconds

Front 682

Which studies of the neck call for contrast injection?

Back 682

•Neck mass
• Lymph nodes
• Parathyroid adenoma
• Parotid gland mass
• Oral pharynx
• Larynx
• Brachial plexus

Front 683

When scanning the brachial plexus, it is advantageous to do what?

Back 683

Inject in the arm which is contralateral to the side of primary interest in order to avoid streak artifacts.

Front 684

Enhances NADPH Oxidase Activity (2)

Possible Answers:
IFNγ, TNF, TGFβ, IFNα/β, CXCL8, CCL2, CCL11

Back 684

IFNγ (from NKs, Th1 and Th0)
TNF (from Macro and Th1)

Front 685

When may IV contrast be used in a CT examination of the chest?

Back 685

• In evaluating masses of the chest
• Lymphoma
• Hilar or cardiac masses
• To visualize vessels
• Pulmonary emboli

Front 686

What is the typical dosage of IV contrast, injection rate and delay time for studies of the chest?

Back 686

100 ml @ 3 ml/sec, with a delay time of approximately 20 to 25 seconds

Front 687

What are some indications for a CT of the abdomen?

Back 687

• Detection of masses
• Lesions
• Vascular abnormalities
• Trauma

Front 688

When scanning an abdomen, it is important to complete scanning before the organ of interest has reached the ______________ phase of enhancement.

Back 688

equilibrium

Front 689

What is the typical dosage of IV contrast, injection rate and delay time for studies of the abdomen?

Back 689

100 to 150 ml @ 2 to 3 ml/sec, with a delay time of approximately 65 to 75 seconds for the liver, 50 to 60 seconds for the pancreas, and 75 to 85 seconds for the kidneys and adrenal glands

Front 690

Delay times will vary from patient to patient depending on what/

Back 690

Cardiac output

Front 691

What do we call the exam frequently performed to differentiate liver lesions with arterial blood supplies from those with venous blood supplies?

Back 691

Bi-phasic study of the liver

Front 692

Describe a bi-phasic liver study.

Back 692

This study collects two complete sets of slices through the liver during two different periods within the non-equilibrium phase of enhancement.

Front 693

How do colon carcinoma metastases in the liver appear in relation to the liver itself?

Back 693

The colon carcinoma metastases in the liver are less vascular than the liver

Front 694

If a tumor is more vascular than the liver, will it be brighter or darker than the liver in the arterial phase of the exam.

Back 694

It will be brighter than the liver

Front 695

Where does the liver receive most of its blood supply from?

Back 695

The Portal vein

Front 696

Tumors of the liver typically receive their blood supply from which vessel?

Back 696

The Hepatic artery

Front 697

When are most liver tumors the most conspicuous?

Back 697

During the portal venous phase of liver enhancement

Front 698

What is the typical dosage of IV contrast, injection rate and delay time for studies of the pelvis?

Back 698

100 ml @ 2 to 3 ml/sec, with a delay time of a few minutes to allow for ureter and bladder enhancement.

Front 699

What conditions require scanning of the pelvis immediately following the injection?

Back 699

• Prostate and ovarian cancer
• Lymphoma
• Melanoma

Front 700

What determines the dose administered to a pediatric patient?

Back 700

Patient weight and the type of scan to be done

Front 701

What would be a typical pediatric dose of IV contrast media for a conventional, serial scan?

Back 701

2 ml per kilogram of body weight

Front 702

What would be a typical pediatric dose of IV contrast media for a helical scan?

Back 702

1.5 ml per kilogram of body weight

Front 703

What is the most accurate way to determine delay times when dealing with pediatric patients?

Back 703

Use bolus tracking software or perform a test bolus timing scan

Front 704

T/F: CTA is most commonly used in the evaluation of veins.

Back 704

False: CTA is most commonly used in the evaluation of arteries

Front 705

What are some reasons for evaluating the arteries with CTA?

Back 705

• Narrowing caused by atherosclerosis
• Aneurysms
• Dissections
• Traumatic injury
• Congenital vascular anomalies
• Effects of vascular treatments

Front 706

In order to keep the concentration of the contrast media in the vessels sufficiently dense, ________ rates of injection of approximately ___ to ___ ml/sec are used in CTA studies.

Back 706

higher, 3 to 5 ml/sec

Front 707

for a CTA exam, ______ slices are collected in the direction of the __________.

Back 707

thin, blood flow

Front 708

What can be increased to scan the vessel more quickly in a CTA examination?

Back 708

Pitch

Front 709

How should the slices from a CTA study be reconstructed?

Back 709

So that they overlap

Front 710

How thick should the slices in a CTA study be?

Back 710

As thin as possible

Front 711

Increasing the overlap of the reconstructed slices increases ____________ and ____________ the effects of partial volume averaging.

Back 711

resolution, decreases

Front 712

As a general rule, what reconstruction interval will produce excellent MPRs, MIPs, or other three-dimensional renderings?

Back 712

A reconstruction interval equal to 1/3 to ½ of the slice thickness

Front 713

T/F: For a CTA examination, only the post-processed images are necessary for a complete diagnostic evaluation.

Back 713

False; The post-processed images should be reviewed along with the axial images for a complete diagnostic evaluation.

Front 714

What is another name for a CT artifact?

Back 714

A CT anomaly

Front 715

What are three general categories of CT artifacts?

Back 715

1. User related artifacts
2. System related artifacts
3. Patient motion artifacts

Front 716

Define Beam Hardening

Back 716

Beam hardening is the increase in average energy of the x-ray beam as it penetrates tissue

Front 717

What do we call an x-ray beam that is comprised of a spectrum of energy levels?

Back 717

Polychromatic

Front 718

The degree of beam hardening is dependant upon the ______________ being penetrated and its _______________.

Back 718

body part, composition

Front 719

The beam is hardened _______ by fat and _______ by bone.

Back 719

less, more

Front 720

Beam hardening is responsible for variations in the ____________ of a given tissue type from the ____________ to the ________ of and image.

Back 720

CT number, periphery to the center

Front 721

T/F: The beam is more affected by beam hardening as it travels through the peripheral tissues and less affected by beam hardening as it penetrates the central tissues.

Back 721

False: The beam is LESS affected by beam hardening as it travels through the peripheral tissues and MORE affected by beam hardening as it penetrates the central tissues.

Front 722

Beam hardening is sometimes called _________ because the signal intensities of tissues on the resulting image have the appearance of the contour of a cup.

Back 722

cupping

Front 723

Give an example of where cupping (beam hardening) might be evident.

Back 723

In the supratentorium of the brain

Front 724

What artifact results when the central tissues are interpreted to be less dense than they actually are and are incorrectly assigned lower CT numbers?

Back 724

Cupping or Beam Hardening

Front 725

In addition to the cupping artifact, beam hardening may be manifested by ______ ________ and regions of decreased density near _______, or through ________ body parts.

Back 725

broad streaks, bones, thick

Front 726

What artifact might be cause by scanning the patients chest or abdomen with their arms at their side?

Back 726

Beam hardening

Front 727

T/F: Beam hardening correction algorithms are a standard feature on most CT scanners today.

Back 727

True

Front 728

What are some techniques to minimize the effects of beam hardening?

Back 728

1. Use a beam hardening correction algorithm
2. Use thinner slices
3. Use diluted contrast agents.

Front 729

How might beam hardening manifest itself in the resultant image?

Back 729

1. Cupping
2. Broad streaks
3. Regions of decreased density

Front 730

How do beam hardening correction algorithms work?

Back 730

They use idealized models of patients composed of fat, muscle, fluid, and bone, but since few patients perfectly match the composition of the model, inaccuracies may result in the correction process

Front 731

The CT numbers and the resultant grey levels are based on what?

Back 731

Upon the linear attenuation coefficient for a voxel of tissue

Front 732

If more than one tissue is contained in a voxel, the CT number is determined by a _____________ of the densities of the contents of the voxel.

Back 732

weighted average

Front 733

What artifact can occur when more than one tissue type is contained in a voxel?

Back 733

Partial volume averaging

Front 734

What artifact results from the mathematical averaging of various attenuation coefficients from several millimeters of different types of tissue?

Back 734

Partial volume averaging

Front 735

How may partial voluming averaging manifest itself in the final CT image?

Back 735

1. It can appear as blurriness at the margins of an object, where the surface of the object curves out of the slice plane
2. It can falsely give the impression of pathology in which vague opacities are the result of a slice through the top or bottom of a rounded structure, such as the top of the aortic arch or the diaphragm

Front 736

How can we minimize the partial voluming effect?

Back 736

Use thinner slices

Front 737

Describe a streak artifact caused by motion.

Back 737

Streak artifacts appear tangential to high contrast edges of the moving structure

Front 738

What motion artifact appears as a double margin of a tissue boundary?

Back 738

A ghost artifact

Front 739

T/F: If rather than two discrete locations, the tissue being scanned gradually becomes displaced over the period of the scan, the resulting images will depict the motion more like a blurring of the tissues rather than a “ghosting artifact”.

Back 739

True

Front 740

Describe a metal artifact.

Back 740

Metal artifacts frequently appear as streaks emanating from the metal object and are caused by a combination of beam hardening, the edge gradient effect, the partial volume effect, and motion

Front 741

T/F: The reconstruction algorithms used to generate the images in CT can not always accurately represent very dense objects (like metal) and interfaces.

Back 741

True

Front 742

What is the best way to minimize metal artifacts?

Back 742

Minimize the metal in the scan FOV

Front 743

T/F: A nasogastric tube may contain metal and should not be removed for a CT scan.

Back 743

True

Front 744

What affects the severity of the metal artifact in the resultant images?

Back 744

• The quantity, composition and shape of the metal object
• The slice thickness
• The number of data sampling points

Front 745

The edge gradient effect is one of the many causes of _________ artifacts in CT images.

Back 745

streak

Front 746

Describe the edge gradient effect.

Back 746

The edge gradient effect occurs when different distinctly different attenuation coefficients are obtained for the same object depending on the vantage point of the projection. This leads to uncertainty in the reconstruction process and manifests itself as streaks which emanate from structures having sharp edges and great differences in density from neighboring tissues

Front 747

Where may the edge gradient effect be seen?

Back 747

• At the interface of bone and soft tissue
• At the interface of air and contrast media
• Sometimes from the edge of the patient table

Front 748

Why streaks from the edge gradient effect less apparent on today’s scanners?

Back 748

Because today’s scanners utilize high data sampling rates and small detector apertures

Front 749

Why would using a smaller detector aperture help minimize the edge gradient effect?

Back 749

The smaller the detector aperture, the lower the probability of capturing photons that have been attenuated to different extents by the same material

Front 750

What are some steps to reduce the edge gradient effect?

Back 750

1. If the structure causing the artifact can be identified, it should be moved or the patient should be repositioned if possible
2. If the scanner allows for an increase in data sampling, or over-sampling, in which a scan arc greater than 360°, is employed, the additional samples will decrease the streak artifact
3. Use thinner slices

Front 751

Describe out-of-field artifacts.

Back 751

Out-of-field artifacts occur because the anatomy outside the scan field-of-view contributes toward the attenuation and hardening of the x-ray beam, but it is ignored during the image reconstruction process

Front 752

T/F: If the anatomy extends beyond the scan field-of-view, out-of-field artifacts may occur.

Back 752

True

Front 753

Out-of-field artifacts may look like ______ or ________ on CT images.

Back 753

Streaks or shading

Front 754

The severity of the out-of-field artifact depends on what?

Back 754

The amount and density of the anatomy outside the SFOV

Front 755

Which artifact results from a faulty or miscalibrated detector element?

Back 755

A ring artifact

Front 756

T/F: On a 3rd generation scanner, if there is a problem with a single detector, it will be represented as a ring on the CT images.

Back 756

True

Front 757

If a detector has an offset difference of as little as _______% with neighboring detectors, a ring artifact may result on the images.

Back 757

0.1%

Front 758

What is one way to tell if you have a faulty detector element?

Back 758

Look at your AP or lateral localizer image and see if there is a straight line traced across the length of the image

Front 759

Where can “tube arcing” occur?

Back 759

• Within the tube
• Outside of the tube within the oil

Front 760

When might tube arcing occur within the tube?

Back 760

When the tube vacuum is compromised

Front 761

When might tube arcing occur outside of the tube?

Back 761

When impurities cause the oil to become electrically conductive

Front 762

Describe the mechanism for arcing within the tube.

Back 762

As the tube ages tungsten gas accumulates inside of the tube. the tungsten gas acts as an alternate pathway from cathode to anode and is the cause of arcing within the tube

Front 763

How will arcing within the tube manifest itself during the early stages of tungsten gas formation?

Back 763

The arcing will be infrequent and not of great energy, therefore only slight signs of random noise or streaks begin to appear in the images.

Front 764

How will arcing within the tube manifest itself during the later stages of tungsten gas formation?

Back 764

As the tungsten gas increases in density the frequency and severity of the arcs will increase and result in more severe noise or more numerous streaks

Front 765

Each time the tube arcs, the ___________ data for that view is distorted.

Back 765

projection

Front 766

T/F: There is no pattern or regularity to the appearance of the artifact caused by arcing within the tube.

Back 766

True

Front 767

What is done by service personal to correct tube arcing from tungsten gas buildup?

Back 767

Generally, the service personal will “burn off” the gas with specific service procedures in order to minimize the occurrence of arcing

Front 768

Arcing of the tube through the oil in the x-ray tube housing is very ________ and ___________.

Back 768

severe and destructive

Front 769

What are the two functions of the special transformer oil that surrounds the x-ray tube?

Back 769

1. It electrically isolates the high voltage anode, filament and cathode connections
2. It serves to transfer the huge quantities of heat normally generated within the tube to a heat exchanger in the gantry

Front 770

T/F: A build-up of air bubbles or other gasses within the oil surrounding the x-ray tube will create an electrically conductive path for the high voltage potential.

Back 770

True

Front 771

Arching in the oil will almost always cause the high voltage generator to shut down due to excessive current.

Back 771

True

Front 772

The image created when arcing occurs outside the tube within the oil contains streaks and noise.

Back 772

False: No image is created when there is arching outside of the tube within the oil since no x-rays are produced

Front 773

T/F: After arcing occurs outside of the tube in the surrounding oil, it is possible that after allowing the tube to cool and resetting the generator, scanning could be continued, although not recommended.

Back 773

True

Front 774

Why is it not recommended to continue scanning after tube arching outside the tube in the surrounding oil?

Back 774

Because it is very destructive to the tube and high voltage generator and because it is not possible to predict the effects from continued arcing on the oil pressure within the tube housing and the oil cooling circuit

Front 775

Describe Cone Beam Artifacts.

Back 775

Cone beam artifacts are associated with multi-row detector scanners that use only simple filtered back projection reconstruction. These artifacts cause peripherally located structures in the image to have a spoke or star-like appearance.

Front 776

The spreading of the x-ray photons along the z-direction is responsible for an artifact called what?

Back 776

A Cone Beam Artifact

Front 777

T/F: Structures in the center of the image are not affected by the cone beam artifact.

Back 777

True

Front 778

T/F: Filtered back projection alone fails to produce acceptable images when the x-ray beam collimation is greater than 20 mm.

Back 778

True