Introduction To Ct

Front 1

The first tomography macines appeared in the ________s

Back 1

1920s

Front 2

The first tomography machines created images by ____?____

Back 2

Capturing multiple exposures on a single piece of film

Front 3

Put computers to work to do the calculations required to make a practical tomography system.

Back 3

Godfrey Newbold Hounsfield

Front 4

The first CT scanner used a ________ rather than film

Back 4

A detector

Front 5

What does a detector do?

Back 5

Converts x-rays into electronic signals

Front 6

3 names used for CT

Back 6

Computed
Computer-assisted
Computerized axial tomography

Front 7

First generation scanners were first used ____?_____

Back 7

In the early 1970s

Front 8

The first generation scanners imaged

Back 8

Only the head

Front 9

The first generation scanners' xray tube produced .....

Back 9

A thin, focused (pencil) beam of x-rays

Front 10

How did the first generation scanners work?

Back 10

The tube and the detector were part of an assemble that moved across the patient and then rotate 1 degree in preparation for the next pass

Front 11

How long did it take the first generation scanners to collect all the data and form an image?

Back 11

5 minutes

Front 12

The first generation scanners used ......

Back 12

a single detector to capture the xrays that traveled through the patient

Front 13

The tube of the second generation scanners generated.....

Back 13

A fan-shaped xray beam

Front 14

The second generation scanners used ______________ to capture the xrays

Back 14

A line (array) of about 30 scanners

Front 15

In the second generation scanners, scan time was ________________ to collect all the data to produce one transaxial image

Back 15

Reduced to about 20 seconds

Front 16

Which generation of scanners set the milestone for CT

Back 16

Third generation

Front 17

When were the third generation scanners introduced?

Back 17

by 1975

Front 18

Third generation scanners used....

Back 18

a large number of detectors arranged along a curve

Front 19

The third generation scanners took ___________ to acquire a transaxial image.

Back 19

Less than one second

Front 20

In the third generations scanners, the tube/detector assembly ...........

Back 20

Rotates around the patient instead of moving across the patient

Front 21

In the fourth generation scanners, the detectors

Back 21

formed a complete circle on the gantry of the scanner that did not rotate

Front 22

In the fourth generation CT scanners only the _______ rotates around the patient.

Back 22

Tube

Front 23

The development of continuous rotation scanners was __?___

Back 23

In the late 1980s

Front 24

Limitations of the early CT scanners

Back 24

Limited in their range of rotation and speed
Heavy cables carried the data from the detectors to the computer
The assembly had to stop after each rotation and its direction reversed

Front 25

Allows the collection of information from more than one transaxial level simultaneously

Back 25

Multi-row detector

Front 26

Multi-row detector

Back 26

Allows the collection of information from more than one transaxial level simultaneously
Reduces the amount of time
Allow for collection of very thin slices
Increases the amount of detail in the images
Excellent images of small structures
Reduce misregistration and artifacts from patient motion

Front 27

Three major system components

Back 27

Computer and operator's console
Gantry
Patient table

Front 28

Four basic functions of the CT computer

Back 28

Control of data acquisition
Image reconstruction
Storage of image data
Image display
(3-D work station)

Front 29

Circular device that houses the xray tube, data acquisition system (DAS) and detector array

Back 29

The gantry

Front 30

The gantry of newer systems also house ......

Back 30

Continuous slip ring
High voltage generator

Front 31

Function of the gantry

Back 31

Collect attenuation measurements

Front 32

Circular device that houses the xray tube, data acquisition system (DAS) and detector array

Back 32

The gantry

Front 33

The gantry is newer scanners also houses ......

Back 33

Continuous slip ring
High voltage generators

Front 34

Aperature

Back 34

Opening in the center of the gantry (approx 28" or 71.1cm wide)

Front 35

Primary difference in the xray tube used for CT and the tube used for conventional xray is ____?____

Back 35

The CT tube is designed to handle and dissapate excessive heat units (about twice as much)

Front 36

Functions of detectors

Back 36

Function as image receptors
Measure amt of radiation transmitted through the body
Converts this into proportional electrical signal

Front 37

Detector types

Back 37

Scintillation (solid state) used now
Ioniztion (xenon gas) not used

Front 38

Termed indexing

Back 38

The movement of the patient table through the gantry which is determined by programming

Front 39

Patient tables are composed of __?__

Back 39

Wood or low density carbon composite

Front 40

Table weight limits

Back 40

Vary from 300 - 600 lbs

Front 41

Exceeding the patient table weight limit can cause......

Back 41

Inaccurate indexing
Damage to table motor
Tabletop breakage, which endangers patient safety

Front 42

The cradle on the patient table does what?

Back 42

Holds head still and used as a positioning aid

Front 43

The operator's control is equipped with

Back 43

Keyboard
Graphic monitor
Other input devices such as the mouse, touch screen

Front 44

Scan perimeters controlled at the operator's control

Back 44

Technique factors
Slice thickness
Table index
Reconstruction algorithm

Front 45

Display monitor

Back 45

Where CT image is viewed in a gray-scale image

Front 46

The brightness values of gray-scale image correspond to ??

Back 46

The pixels and CT numbers that they represent

Front 47

Allows viewer of the display monitor to alter contrast of the displayed image

Back 47

Windowing (window width and window level)

Front 48

The multiple imaging/windows of the display monitor show

Back 48

Anterior view (scout)
High contrast (black & whites)
Bone window
Low contrast (soft tissue)

Front 49

Benefits of CT

Back 49

-Distinguish between small structures that have similar xray densities
-CT can distinguish tissues with differences in density of less than 0.5% (density of about 10% is needed to see a difference on conventional radiographs)
-Speed (20 to 100 seconds)
(patient movement is minimized)

Front 50

Digital imaging modality

Back 50

-Even after the images are printed on film, they can be modified and re-filmed
-Store/transfer digital files to other locations

Front 51

Localizer scans

Back 51

-Scout films
-Provides an overview of the area of interest

Front 52

Conventional or serial scans

Back 52

-Collects attenuation data from a single cross-sectional slice
-Table then moves to the next slice position and the tubes rotates again

Front 53

Helical or spiral scans

Back 53

Xray tube remains on for as long as 100 seconds, rotating around the patient through multiple projections while the patient table moves through the gantry.

Front 54

Post-processing

Back 54

Allows the anatomical data to be reformatted to aid in the diagnosis without having to perform additional scans

Front 55

Filtered back projection

Back 55

-Sums the attenuation information from all projections
-Without filtering, the edges of the structures would appear blurry and the structures themselves would appear grainy or "noisy"

Front 56

Sharp reconstruction filter

Back 56

Improves the definition of the edges of the structures

Front 57

Smooth reconstruction filter

Back 57

Minimizes the grainy appearance of "noise" so the contrast between the tissues can be distinguished

Front 58

Pixel element

Back 58

Taking the attenuation information from the localizer scan, serial scan or helical scan and preparing it to be displayed digitally

Front 59

Image matrix

Back 59

Data representing the anatomical region of interest must be divided into rows and columns

Front 60

Picture element or pixel

Back 60

Each are of the matrix formed by the intersection of a row and column

Front 61

A CT image is composed of __?__

Back 61

Pixels or tiny picture elements

Front 62

Hounsfield Scale

Back 62

Organized the tissues of the body according to their attenuation properties

Front 63

In the Hounsfield scale, the _____ the number the _______ the density of the stucture.

Back 63

the higher the number - the greater the density

Front 64

HU for water

Back 64

0

Front 65

HU for air

Back 65

-1000

Front 66

CT number for soft tissues

Back 66

Approx 40 HU

Front 67

CT numbers above 100 indicate __?__

Back 67

Calcification

Front 68

Dense bone can have values as high as __?__ HUs

Back 68

1000 HU

Front 69

CT number

Back 69

Organizes the tissues of the body according to their attenuation properties

Front 70

Higher CT numbers correspond to ___?___

Back 70

"Whiter" shades of gray

Front 71

Lower CT numbers correspond to __?__

Back 71

"Blacker" shades of gray

Front 72

Determinants of CT Image quality

Back 72

Contrast
Resolution
Noise
KvP/mAs
Slice thickness
Table increments
Pitch
Field of View (FOV)
Matrix

Front 73

A key factor that controls the contrast of a CT image is __?__

Back 73

The energy level of the xray photons

Front 74

Contrast

Back 74

Ability to differentiate small density differences between structures on a CT image

Front 75

Resolution

Back 75

A measure of the smallest object that we can see, or resolve, in the image

Front 76

Things that effect resolution in a CT image

Back 76

- Size of a pixel
- Slice thickness
- Reconstruction filters

Front 77

Thinner slice = _____ technique

Back 77

Increased technique

Front 78

Thicker slice = ______ technique

Back 78

Decreased technique

Front 79

Noise

Back 79

Grainy appearance
(too few photons)

Front 80

Increasing the number of photons in the CT scan will _______ the appearance of noise on the image.

Back 80

Decrease

Front 81

The simplest way of increasing the number of photons that contribute to the pixels in the image is to .............

Back 81

Increase the tube current or the scan time

Front 82

Kilovoltage - kVp

Back 82

The parameter that controls the contrast in a CT image

Front 83

The energy of the electrons in the xray tube is determined by the _________ and in turn determines the energy of the xray photons

Back 83

Voltage

Front 84

The amount of _____ controls the temperature of the cathode filament in the tube.

Back 84

Current

Front 85

Higher mAs is associated with ___?___

Back 85

An increased radiation dose to the patient

Front 86

Slice thickness is partially determined by __?___

Back 86

The size of the focal spot

Front 87

Thick slices result in ______ radiation dose to the patient

Back 87

Less

Front 88

Thin slices result in _______ radiation dose to the patient

Back 88

More

Front 89

Table increment

Back 89

Distance the patient table travels between slices

Front 90

Pitch

Back 90

Equals the movement of the patient table in one gantry rotation divided by the slice thickness

Front 91

FOV

Back 91

Field of view
(scan FOV and reconstruction FOV)

Front 92

The image matrix for CT is usually ______

Back 92

512 x 512