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370 Cards in this Set

  • Front
  • Back

Each CT slice represents a specific plane in the patient's body, referred to as the ______ axis.

Z
What does the Z axis determine?
The thickness of the slice
A pixel's width is indicated by the letter __.
X
A pixel's height is indicated by the letter __.
Y
If the Z axis is taken into consideration in regards to a pixel, the result is :
A cube, referred to as a voxel
The amount of the xray beam that is scattered or absorbed per unit thickness of the absorber is expressed by ___________.
The linear attenuation coefficent
What is the HU for air?
-1000
What is the HU for dense bone?
1000
The process in CT by which different tissue attenuations are averaged to produce one less-accurate pixel reading is called _____________.
Volume averaging or the partial volume effect
How would decreasing slice thickness impact patient dose?
Increases the dose
What area of the anode is struck with electrons to produce the xray beam?
Focal spot
What is the term for the ability of the tube to rid itself of heat?
Heat dissipation
What is the term for the ability of the tube to withstand heat?
Heat capacity
Each detector cell is sampled many times per second by the __________.
Data Acquisition System (DAS)
The digital data from the DAS is transmitted to the ____.
Central processing unit - CPU
Which is not a synonym for the preliminary/localizer image?
a. Topogram
b. Scout
c. Scanogram
d. Spiral
d. Spiral
The ability of a system to differentiate, on the image, objects with similar densities is known as:
a. high contrast resolution
b. low contrast resolution
c. spatial resolution
d. temporal resolution
b. low contrast resolution
Each two dimensional square of data that make up the CT image is called a:
Pixel
How many pixels are contained in a 1,024 matrix image?
a. 1,024
b. 2,048
c. 262,144
d. 1,048,576
d. 1,048,576
Define beam attenuation.
The phenomenon by which an xray beam passing through a structure is decreased in intensity or amount because of absorption and interaction with matter.
What is the HU of water?
0
The xray beam sources for CT produce xray energy that is polychromatic. What does this mean?
The beam comprises photons with varying energies
Scan thickness is PRIMARILY important for the part it plays in:
a. noise reduction
b. the contrast scale
c. detector aperture opening
d. volume averaging
d. volume averaging

Thinner slices reduce volume averaging by decreasing the amount of patient information included in each voxel.
How many CT numbers are assigned to each pixel in the image matrix?
One
What is another name for raw data?
Scan data
What are the typical gantry sizes?
70 to 90 cm
The power capacity of generators is listed in ___.
kW - kilowatts
Anode heat capacity is measured in :
million heat units (MHU)
What is the typical size range of the aperture?
70-90 cm
How does a small focal spot impact spatial resolution?
Increases spatial resolution
Anode heat capacity is measured in what units?
Million heat units (MHU)
Anode heat dissipation rate is measured in what units?
Thousand heat units (KHU)
These filters reduce the beam intensity at the periphery of the beam, corresponding to the thinner areas of a patient's anatomy.
Bow tie filter
What is the geometric efficiency of a detector?
Refers to the amount ot space occupied by the detector collimator plates relative to the surface area of the detector.
What is the capture efficiency of a detector?
Refers to the ability with which the detector obtains x-ray beams that have passed through the patient
What is the absorbtion efficiency of a detector?
Refers to the number of photons absorbed by the detector and is dependent on the physical properties of the detector face
What is dynamic range?
The ratio of the maximum signal measured to the minimum signal the detectors can measure
What are all new detectors made of?
Solid-state crystal
What is the difference between solid state crystal detectors and the xenon gas filled detectors?
Xenon gas detectors are less effiecient, less expensive to produce, easier to calibrate, and highly stable.
Solid-state detectors are also called _________.
Scintillation detectors
Why are solid state detectors also called scintillation detectors?
Because they use a crystal that fluoresces when struck by an xray photon.
What transforms the light energy from an x-ray photon into an electrical energy in a solid state detector?
Photodiode
True or false. Older solid state detectors produced an afterglow.
True, although brief.
Which detectors are more sensitive to temperature and moisture fluctuation, solid state or gas filled?
Solid state
How is detector spacing measured?
From the middle of one to the middle of the neighboring detector. This accounts for the spacing bar placed between each detector element.
What is the size of the detector opening called?
Aperture
What generation scanner design uses a fan-shaped beam?
Third generation
What disadvantage does the third generation scanner have compared to the fourth generation?
More frequent ring artifact
What are disadvantages of fourth generation scanners?
Beacuse the beam does not strike the detectors at the same time, motion artifacts are more of a problem. Also, because the tube is closer to the patient, the same technique will produce more dose.
The ___________ measures the number of photons that strike the detector, converts the information to a digital signal, and sends the signal to the computer.
Data acquisition system (DAS)
Where is the DAS located?
In the gantry near the detectors
What component converts the analog signals into a digital format?
Analog digital converter (ADC)
What is the sample rate, sampling rate, or sampling frequency?
The rate at which detectors are sampled (many times per second) by the DAS (data acquisition system)
True or false. Three phase generators are not housed in the gantry.
True. They are stand alone units located near the gantry and require cables.
The power capacity of the generator is measured in:
kW (kilowatts)
What is a disadvantage of a small focal spot?
Reduced heat capacity
The ability of the tube to withstand by-product heat is called:
heat capacity
What is geometric efficiency controlled by?
Detector spacing and aperture
Why are xenon gas detectors less efficient?
They are cased in aluminum which adds additional filtration to the xray photons.
What is Fast Fourier transform (FFT)?
An efficient algorithm that is used in image analysis and many other applications.
What is interpolation? Linear interpolation?
A mathematical method of estimating the value of an unknown value using the known values on either side of the value. Linear interpolation assumes that an unknown point falls along a straight line between two known points.
What is serial access memory (SAM)?
The opposite of RAM, stores data which can only be accessed sequentially.
What is write once read only memory (WORM)?
It does not allow saved information to be rewritten, reformatted or erased
Image reconstruction that is automatically produced during scanning is called ______.
Prospective reconstruction
The detector reads each arriving ray and measures how much of the beam is attenuated. This measurement is called a ______.
Ray sum
A complete set of ray sums is a:
View
The system accounts for the attenuation properties of each ray sum and correlates them with the position of the ray. The result of this correlation is called:
An attenuation profile (created for each view in the scan)
The information from all attenuation profiles is projected onto a matrix. The process of converting the data from the attenuation profile to a matrix is known as:
Back projection
The process of applying a filter function to an attenuation profile is called:
Convolution
How can changing the DFOV (display field of view) affect image quality?
Changes the amount of raw data that is averaged together for each pixel.
"A precise set of steps to be performed in a specific order to solve a prolem" is the definition of _______.
Algorithm
What is interpolation?
A mathematical method of estimating an unknown value using the known values on either side of the unknown.
What is the function of the CPU (Central Processing Unit)?
Interprets computer program instructions and sequences tasks
The DAS reads each arriving ray and measures how much of the beam has been attenuated. This is called:
A ray sum.
How many shades of gray can a monitor display?
256
The number of Hounsfield units assigned to each level of gray is determined by:
Window width
The _______ selects the range of HU that will be displayed.
Window level
All values greater than the window level range selected will appear ______ on the image.
White
All values less than the window level range selected will appear ______ on the image.
Black
How many shades of gray can a monitor display?
256
The number of Hounsfield units assigned to each level of gray is determined by:
Window width
The _______ selects the range of HU that will be displayed.
Window level
All values greater than the window level range selected will appear ______ on the image.
White
All values less than the window level range selected will appear ______ on the image.
Black
What is the advantage of wider window settings?
They decrease contrast thus minimizing noise.
Tissue types with similar densities should be imaged using _______ window width.
Narrow window width (50 - 500 HU)
Wide window widths are beneficial for imaging what type of tissues?
Tissue types that vary greatly (500 - 2000 HU)
What is standard deviation?
The variance of CT numbers within an ROI
What is the function of a digital to analog converter?
Converts the digital signal from the computer into an analog signal for the monitor.
If the tissue of interest is the liver, what is the best approximate window level setting?
50. The window level should be set at a point that is roughly the same value as the average atttenuation number of the tissue of interest. Window level selects the center value while the window width selects the range of Hounsfield values displayed.
If the standard deviation within an ROI is 0, what does this mean about the structure being measured?
It is very homogenous
What is a surview?
Localizer image
What is a pilot image?
Localizer
What is a scanogram?
Localizer image
What is another term for topogram?
Localizer
An AP localizer image ensures proper centering in the ___ direction.
x
A lateral localizer image ensures proper centering in the ___ direction.
y
Including all the areas to be scanned on the localizer image ensures that they lie within the scannable range or ___ direction.
z
What type of scanner had the "fan beam"?
Single Detector row systems (SDCT)
One gantry rotation produced data for one image slice in what type of system?
SDCT (Single Detector CT)
What type of scanners produce a cone beam?
Multi detector row systems (MDCT)
True or false. MDCT can be used for helical scanning.
True
In some MDCT systems the center rows of the detectors are thinner than those at the periphery. These variable width detector rows are also called by these names.
Adaptive arrays, nonuniform arrays or hybrid arrays
What are the three ingredients that define a helical scan process?
A continually rotating tube, constant xray output, and uninterrupted table movement
What are three other names for helical scanning?
Spiral, volumetric, and continuous acquisition
What is a disadvantage of interpolation?
A slight loss of resolution
What is helical interpolation?
"Unslanting" of helical images so rather than connecting at a slant similar to a spring shape they are more like a sliced sausage or axials
What is another name of the effective slice thickness?
Slice sensitivity profile (SSP)
Define pitch.
The travel distance of the CT scan table per 360 degree rotation of the x-ray tube, divided by the x-ray beam collimation width
How can helical interpolation effect slice thickness?
Can result in a slice that is wider than that selected by the operator.
How does pitch impact image resolution?
As pitch is increased, there is a greater loss of image resolution due to the slice angle increasing (spring being stretched) there is greater need for interpolation.
When the table feed and the beam collimation are identical, what would the pitch be?
1
How does increasing pitch impact patient radiation dose?
Increasing pitch decreases dose
How does a decrease in pitch impact image sharpness?
Decreasing pitch increases sharpness
In an 64 slice MDCT scanner, with .5 mm slice thickness and a table feed of 48 mm per rotation, what would the pitch be? What is the equation?
48/(64 x .5) = 1.5 pitch
In an MDCT helical scan, if the pitch is 1.5, acquisition time 20 seconds, 1 mm slice thickness, 4 slices per rotation and a gantry rotation is .5 seconds, how much anatomy is covered? What is the equation?
1.5 x 20 sec x 1 mm/.5 sec x (1 x 4) = 240 mm
The interscan delay inherent in an axial scan method is caused by which factor?
Table movement between data acquisitions
The practice of grouping more than one axial scan in a single breath hold is referred to as:
Clustering
Compared with helical scanning, what are the primary disadvantages to the axial method of scanning?
Total examination time is longer and data reconstruction is more limited
What is it called when a patient breathes differently with each data acquisition and areas of anatomy seem to be misplaced in the z axis?
Misregistration
True or false. Another term for helical scanning is dynamic scanning.
False
What is the goal of helical interpolation?
Take the slant and the blur out of the helical image so that they closely resemble images taken from axial methods.
What is the pitch in this scenario: 16 slice scanner, .5 mm slice thickness, table movement of 12 mm per rotation? What is the equation?
12/(16 x .5)= 1.5
How much anatomy will be covered in a helical scan when: 15 sec acquisition time, .5 sec gantry rotation time, 2 mm slice thickness, 4 slices per rotation, pitch of 1.5? What is the equation?
Pitch x acquisition time x 1/rotation time x (slice thickness x slices per rotation) therefore 1.5 x 15 x 1/.5 sec x (2mm x 4) = 360 mm
The current of electrons that flow from the tube filament to strike the anode is measured in __________.
mA
Increasing the mA increases the number of __________.
Electrons that will produce x-ray photons
How does the filament size impact the amount of penumbra?
Small filament = less penumbra
Small filaments are typically used for mA up to what amount?
350
What is the difference in the definition of "scan time" when referring to SDCT and MDCT?
For SDCT, scan time is the time the x-ray beam is on for the collection of data for each slice or the time it takes for the gantry to make a complete 360 degree rotation. For MDCT, it is the time it takes for the tube to make a 360 degree rotation although many slices may be produced.
Routine body CT scans for adults typically use how much kVp?
120-140 kVp
Pediatric patients are often scanned using how much kVp?
80 kVp
True or false. Dose is reduced if the kVp is reduced and the mAs held constant.
True
What does the term "coupled" mean?
An image is "coupled" with the dose if the dose is too high and a radiograph is overexposed causing the image to be too dark.
Explain the "uncoupling" effect.
In CT the image quality is "uncoupled" from the dose so that even when a technique that is too high is selected, a good image results. This effect makes it difficult to know when a dose is higher than necessary.
This type of view determines the area, within the gantry, for which raw data are acquired. This type of data are always acquired around the gantry's isocenter.
SFOV or scan field of view, scan data
This view determines how much, and what section, of the collected raw data are used to create an image.
Display field of view or DFOV
What type of algorithms help to reduce the appearance of artifacts by reducing the difference between adjacent pixels, but sacrifice spatial resolution?
Smoothing algorithms
What type of filters accentuate the difference between neighboring pixels to optimize spatial resolution, but make sacrifices in low-contrast resolution?
Bone or detail filters
True or false. Pitch settings can vary depending on manufacturer and detector row number and configuration.
True
What is a half scan or partial scan?
Images are created from less than a 360 degree rotation, typically 180 degrees plus the degree of the arc of the fan angle.
What is an overscan?
Uses information from more than a 360 degree rotation. It adds approximately the width of the FOV to the full scan, resulting in a 400 degree rotation. Commonly used in fourth generation scanners.
What is image fidelity?
Image accuracy
What is the difference between detail (or high-contrast) resolution and contrast resolution?
Detail or high contrast resolution is the ability to resolve (as separate objects) small, high-contrast objects. Contrast resolution is the ability to differentiate between objects with very similar densities as their background.
What is another term for detail resolution? Define it.
Spatial resolution. The system's ability to resolve, as separate forms, small objects placed very close together.
What are the two methods of measuring spatial resolution?
Measuring directly with a line pairs phantom or calculating from analyzing the spread of information within the system (also known as the modulation transfer function or MTF).
What is the modulation transfer function or MTF used for?
Measuring spatial resolution by analyzing the spread of information within the system. MTF is the ratio of the accuracy of the image compared with the actual object scanned.
What is a line pair?
A line and the space between lines. For example, if 20 lines can be seen in a 1 cm section in an image of a phantom, the spatial resolution is 20 line pairs per centimeter (lp/cm)
The number of line pairs visible per unit length is also called what?
Spatial frequency
What is spatial frequency?
The number of line pairs visible per unit length or how frequently an object will fit into a given space.
How does the size of objects relate to their spatial frequency?
Large objects will have a low spatial frequency
True or false. MTF or modulation transfer frequency is a method of describing spatial frequency also used in radiography
True
What is modulation transfer function or MTF?
The ratio of the accuracy of the image compared with the actual object scanned
If an image reproduced an object exactly, what would the MTF value be?
1
If an image were blank and contained no information about an object, what would the MTF value be?
Zero
On an MTF graph, what is represented on the x axis and y axis?
Spatial frequency on the x and MTF along the y axis
What would an MTF curve that extends farther to the right indicate?
Higher spatial resolution, which means the imaging system is better able to reproduce small objects
How does CT compare to conventional radiography in terms of spatial resolution?
CT has significantly worse spatial resolution. It is the contrast resolution that distinguishes CT from other modalities.
Spatial resolution of a CT image in the xy direction is called what?
In-plane resolution
Spatial resolution of a CT image in the z direction is called what?
Longitudinal resolution
What is the equation for determining pixel size?
DFOV/Matrix size = Pixel size
What letters represent the width and length of a pixel?
x=width
y=length
Why are large focal spots less desirable?
Cause more geometric unsharpness and reduced spatial resolution
How would increasing the pitch impact spatial resolution?
Reduces the resolution
Spatial resolution decreases when the pitch is increased. Is this more pronounced on MDCT or SDCT?
SDCT
________ is the ability to differentiate a structure that varies only slightly in density from its surrounding.
Contrast resolution (or low-contrast resolution)
CT can differentiate an object with a __% contrast variation or a __ HU difference.
.5% or 5 HU
Doubling the mAs increases the signal to noise ratio (SNR) by how much?
40%
How does slice thickness impact SNR?
Thicker slices have a better SNR and therefore appear less noisy
Would contrast resolution be high or low for a bone window?
Low
How would a soft tissue algorithm impact contrast resolution?
Improves contrast resolution
What is contrast-detail response?
The relationship between object size and visibility
With regards to image quality, what does temporal mean?
The characteristic of being limited by time
What is temporal resolution?
How rapidly data is acquired
What controls temporal resolution?
Gantry rotation speed, the number of detector channels in the system, and the speed with which the system can record changing signals
How is temporal resolution of a CT system reported?
ms (milliseconds)
What is a partial scan?
A scan that collects data from 180 degree tube arc, plus the degree of arc of the fan angle
What is the true test of the quality of a specific image?
Whether it serves the purpose for which it was acquired
What two main features are assessed to measure image quality?
Spatial resolution and contrast resolution
What is the term for the ability to differentiate on an image a structure that varies only slightly in density from its surrounding?
Contrast resolution
What is spatial frequency?
How frequently an object will fit into a given space. Large objects will have low spatial frequency.
What is modulation transfer function (MTF)?
a measure of the capability of the scanner to produce an image that accurately reflects the object scanned
How is pixel size calculated?
Divide the DFOV by the matrix size
What is an isotropic voxel?
A cube, measuring the same on the x,y, and z axis
If a water phantom image is noisy, what went wrong?
mAs is too low or slice thickness is too thin
What does a line pairs phantom measure?
Spatial resolution
How is the slice thickness accuracy of a scanner be evaluated?
Using a phantom that includes a ramp, spiral, or step wedge. This test is usually performed semiannually.
What is cross field uniformity?
The ability of the scanner to yield the same CT number in a homogeneous object (i.e., water phantom) regardless of the location of the region of interest (ROI).
What is linearity?
The relationship between CT numbers and the linear attenuation values of the scanned object at a designated kVp value. This is tested semiannually with a phantom containing a variety of densities.
What causes beam hardening artifact?
When lower energy photons are preferentially absorbed, leaving only the higher energy beams to strike the detector caused by more dense objects.
What do beam hardening artifacts look like?
Cupping or streaking
What is the best strategy available to the tech to avoid beam hardening?
Reducing scan field of view (SFOV).
What causes partial volume artifact?
When a dense object lies on the edge of the field of view so it only shows in a small number of images. The inconsistencies between the views cause shading artifacts.
What can a tech do to reduce partial volume artifact?
Use thinner slices
What type of artifact is caused by undersampling?
Aliasing artifact
What do aliasing artifacts look like?
Fine stripes appear to radiate from a dense structure
How can aliasing artifacts be prevented?
Increasing scan time or reducing pitch
What type of artifacts occur from the edge gradient effect?
Streak artifacts arise from irregularly shaped objects that have a pronounced difference in density from surrounding structures.
How can edge gradient artifacts be avoided?
They are largely unavoidable, but are somewhat reduced by reduced by thinner slices. Using low HU value oral contrast, such as water, in place of barium can eliminate the streak artifacts from the GI tract.
What causes ring artifacts?
Occur primarily with third generation scanners. They are caused by faulty or miscalibrated detector elements. Sometimes eliminated by calibration.
What causes tube arcing?
An electrical current surge
What causes helical interpolation artifacts?
Can occur in spiral scans when higher pitches are used.
What does helical interpolation look like?
Result in subtle inaccuracies in CT number and can lead to interpretation errors.
What can be done to avoid helical interpolation?
Use a low pitch when possible
What do windmill artifacts look like?
Streaks or bright and dark shading near areas of large density differences.
What causes windmill artifacts?
Only on MDCT helical systems. They are attributed to the wider collimation that is required to accommodate the larger number of detector channels. This can also cause fan beam artifacts.
How often is the accuracy of a scanner's slice thickness tested?
Semiannually
A water phantom is scanned and several ROIs are placed in the resulting image. the ROIs placed at the perimeter of the image measure differently from the ROIs near the center. This indicates a problem with the _________.
Cross-field uniformity
A water phantom is scanned and several ROIs are placed in the resulting image. The standard deviation measurements from the ROIs range from 15 to 25. What can be said about this and what needs to be changed?
It is noisy. The standard deviation is 10 or less. Increasing the technique or using a wider slice thickness will help reduce noise.
What can be done to improve the linearity of a CT system?
Daily calibrations
What type of artifact may be caused by air in the stomach?
Edge gradient artifact
Surface rendering (SR) is also called this.
Shadow surface display
This is a form of volume rendering (VR) that is designed to look inside the lumen of a structure.
Endoluminal imaging
What are segmentation errors?
When important vessels or other structures are inadvertently edited out of the data set
What causes stair step artifacts?
When voxels are not isotropic
Raw data that results from an MDCT scan acquisition is used so that the 1 mm slices are combined to produce thicker slices for viewing. This is called what?
Image reconstruction
How can we determine whether a voxel is isotropic, what is the formula?
DFOV in mm/512
When would overlapping slices not be beneficial?
When the voxels from the source data are isotropic, or near isotropic, overlaping would provide little benefit. To determine whether a voxel is isotropic, calculate pixel size (DFOV in mm/512), then compare the pixel size to the slice thickness. When thickness is considerably greater than pixel size, it would not be beneficial.
Any process that uses raw data is called:
Reconstruction
Reformation uses only this type of data.
Image data
Raw data that results from an MDCT scan acquisition is used so that the 1 mm slices are combined to produce thicker slices for viewing. What is this called?
Image reconstruction
In what situation would overlapping recons for image rendering not be indicated?
a. DFOV=25 with .5 mm slices
b. DFOV=35 with 2 mm slices
c. DFOV=42 with 5 mm slices
d. DFOV=45 with 7 mm slices
a. When slice thickness is greater than the pixel size overlapping would be beneficial. (Pixel size = DFOV in mm/512 *unsure on specific formula)
True or false. Assume the raw data is available. When source images vary in gantry tilt, it is impossible to create an MPR.
True
Can MPRs be created at a separate workstation as well as the operator's console?
Yes
True or false. Scanner-created MPRs, in most cases, only generate straight sagittal and coronals.
True
Why would workstation-created MPRs slow down PACs?
The highest quality MPRs require the thinnest slices to be sent to the workstation, uses more data.
What is another name for surface rendering?
Shaded surface display
In creating a surface rendered image, what can happen if the threshold is set too narrow?
Actual protruding structures can be imperceptible
What happens if the surface rendering threshold is set too high?
The image will include unwanted structures that may obscure the area of interest
What happens if the surface rendering threshold is set too low?
This may cause important structures to be omitted from the display.
Why would you not want a MIP to visualize the bronchial tree?
MIPs are best used for higher attenuation such as bone, calcifications, and contrast filled structures.
Why would you want a MinIP to view the bronchial tree?
MinIP involves selecting voxels with minimum values for display. These are useful for displaying low attenuation structures.
What is the favored 3D imaging technique in CT?
Volume rendering
The process of selectively removing or isolating information from the 3D data set is referred to as:
segmentation
The collection, classification, storage, retrieval, and dessemination of recorded information is known as:
informatics
What does CPOE stand for?
Computerized physician (or provider) order entry
What does EHR stand for?
Electronic health record
What does DICOM stand for?
Digital imaging and communications in medicine
Which organization works to develop universal standards for clinical and administrative data throughout the healthcare arena?
Health Level Seven (HL7)
What does RAID stand for and what does a RAID do?
Redundant array of inexpensive disks or drives. Is a storage solution that caopitalizes on the fact that data stored on hard disks can be accessed quickly and reliably.
Which electronic system allows clinicians to imput an electronic order for an exam and transmits that order to the CT department?
CPOE
The computers that are integral to the functioning of the PACS are referred to as:
core servers
What does RAID stand for and what does a RAID do?
Redundant array of inexpensive disks or drives. Is a storage solution that capitalizes on the fact that data stored on hard disks can be accessed quickly and reliably.
A scheme that compresses an image without any data loss of information when the image is decompressed is called:
Lossless
What does RAID stand for and what does a RAID do?
Redundant array of inexpensive disks or drives. Is a storage solution that caopitalizes on the fact that data stored on hard disks can be accessed quickly and reliably.
Which electronic system allows clinicians to imput an electronic order for an exam and transmits that order to the CT department?
CPOE
The computers that are integral to the functioning of the PACS are referred to as:
core servers
A scheme that compresses an image without any data loss of information when the image is decompressed is called:
Lossless
What is the normal range for BUN time?
7 - 25 mg/dL
What is the normal range for creatinine?
.6 - 1.7 mg/dL
What is the normal range for prothrombin time or PT?
11 - 14 seconds
What is the normal range for partial thromboplastin time or PTT?
25 - 35 seconds
What is the normal range for platelet count?
150,000 - 400,000
What relevance do PT, PTT, and platelet count have in CT?
They indicate blood coagulation ability which is important for biopsy or drain procedures.
What is the average and normal range of oral temperature?
Average - 98.7 F, 37.0 C and Normal - 96.8 F to 100.4 F, also 36.0 C to 38.0
What is the average and normal range of rectal temperature?
Average: 99.1 F or 37.7 C
Normal range: 97.2 - 100.8 F or 36.7 - 38.7 C
What is the average and normal range of axillary temperature?
Average: 97.7 F or 36.4 C
Normal range: 95.8 - 99.4 F or 35.4 - 37.4 C
_________ is defined as the alternate expansion and recoil of an artery.
Pulse
What is the average pulse rate for an adult?
60-100 bpm however in an athletic adult it may be between 45 and 60
What is the average pulse for a child?
95-110 bpm
What is the average pulse of an infant?
100-160 bpm
What is the normal respiratory rate for an adult?
14-20
What is the normal respiratory rate for an adolescent?
18-22
What is the normal respiratory rate for children?
22-28
What is the normal respiratory rate for infants?
30 or greater
__________ is defined as the pressure exerted by circulating blood on the walls of the vessels.
Blood pressure
_________ is defined as the peak blood pressure.
Systolic
________ is defined as the lowest blood pressure.
Diastolic
What is the typical resting blood pressure of an adult?
120/80 mm Hg
What is the normal range for blood pressure in a healthy adult?
90-140 mm Hg systolic and 65-130 mm Hg diastolic
What is the normal blood pressure range for children?
65-130 mm Hg systolic and 45-85 mm Hg diastolic
Why would a patient with a history of thyroid issues be concerned about receiving IV contrast?
In patients with hyperthyroidism, contrast can intensify thyroid toxicosis (excessive thyroid hormone) which could initiate a thyroid storm.
What is the atomic number for iodine?
53
What is the minimal visible detectable difference to identify normal versus pathologic tissue?
10 HU
What does isotonic mean?
The medication has nearly the same amount of particles in solution, per unit of liquid, as blood.
Contrast agents have up to _____ times the number of particles in solution, per unit of liquid, as blood.
Seven times
The structural property of a liquid regarding the number of particles in solution, per unit of liquid, compared with blood is known as:
Osmolality
How is osmolality measured?
Milliosmoles per kilogram (mOsm/kg) of water
What is the osmolality of blood plasma?
290 mOsm/kg water
Most iodinated contrast agents have a greater osmolality than blood plasma therefore, they are called:
hyperosmolar or hypertonic
What does HOCM stand for?
High osmolality contrast media
What is the osmolality range of older iodinated agents?
1,300 to 2,140 mOsm/kg
What does LOCM stand for?
Low osmolality contrast media
The iodinated contrast introduced in the 1980's has the osmolality range of:
600 to 850 mOsm/kg
What does IOCM stand for?
Isosmolar contrast media
In what year was Visipaque introduced?
1996
True or false. Visipaque is isosmolar.
True
What is a common reaction when a bolus injection of a hypertonic contrast agent is injected?
Mild hydration as a result of the rapid increase in the osmolality of the plasma and then the osmolality equalizing in the body.
The physical property that is described as the thickness or friction of the fluid as it flows is the definition of:
Viscosity
What are two properties that affect viscosity?
Molecular structure and concentration
The _________ of contrast can be significantly decreased by heating the liquid to body temperature prior to injection.
Viscosity
The molecules contained in this type of contrast media do not dissociate. The entire molecule remains intact as it passes through, and is excreted from, the body.
Nonionic contrast
Most nonionic contrast agents have this type of osmolality.
Low osmolality, however these two terms are not synonymous
IV contrast is normally eliminated within this time frame, assuming normal kidney function.
2 hours
LOCM are measured in:
Milligrams of iodine per milliliter (mgI/mgL)
HOCM are measured in:
Percent weight per volume
True or false. A concentration of 400 mg/mL injected at 3 mL/s will provide the same enhancement as a concentration of 300 mg/mL injected at 4 mL/s.
True
What is the typical limit of contrast to avoid overdose?
200 mL with a concentration of 320 mgI/mL (a total of 64 grams of iodine)
What is the most common formula used to determine contrast delivery amount to a child?
2 mL/kg
How much of a IV contrast agent given to a lactating mother is excreted into breast milk?
Less than 1% and less than 1% of the iodine ingested is absorbed by the infants GI tract.
What are the risks of a fatal reaction from IV contrast?
.9 per 100,000 (<0.001%)
What are the two types of contrast reactions?
Chemotoxic and idiosyncratic
What are chemotoxic reactions that can occur from contrast injection?
They result from the physicochemical properties of the contrast media, the dose, and speed of injection. Hemodynamic (i.e. relating to the blood circulation) disturbances and injuries to organs or vessels perfused by the contrast are included. Nephropathy is included.
What are idiosyncratic reactions that can occur from contrast injection?
Most often occur within 1 hour of injection and are not related to the dose. They are anaphylactoid reactions. Nausea, vomiting, warmth, anxiety, hives, welling, difficulty breathing, etc.
What is the reported rate of adverse side effects with HOCM?
5 to 12%
In those people with asthma, the risk of an adverse reaction to HOCM increases by ______ times and LOCM ________ times.
HOCM: 8 times
LOCM: 5 times
What does CIN stand for?
Contrast induced neuropathy
What does ARF stand for?
Acute renal failure
How much of the total arterial blood pumped by the heart is received by the kidneys?
20-25%
Which part of the kidney produces urine by filtering out from the blood small molecules and ions and then reclaiming the needed amounts.
The nephron
What is the definition of kidney clearance?
The ability of the kidneys to remove a substance from the blood. The clearance is the volume of plasma cleared by a specific substance in a given period of time.
What does GFR stand for?
Glomerular filtration rate
What does ERPF stand for?
Effective renal plasma flow
What is the most serious adverse effect of metformin if continued following contrast administration?
The potential for the development of lactic acidosis
Lactic acidosis in patients taking metformin following contrast administration has a fatality rate of __%.
50%
What is the half-life of iodinated contrast media in patients with severe renal dysfunction?
Can be more than 30 hours
What impact does contrast have on the thyroid in patients with hypothyroidism or autoimmune (Hashimoto) thyroiditis?
There may be a small, temporary reduction in thyroid function but does not require additional treatment
Iodinated contrast can impact a thyroid uptake study. How long should the patient wait before scheduling an uptake test after a CT scan?
2 weeks
Iodinated contrast has been known to cause seizures in those that have this type of cancer.
Mets to the brain
What is a negative contrast agent?
Air
What are the statistics of allergic reactions to barium sulfate?
1 in 500,000 and are usually attributed to the additives, such as flavoring
This antispasmodic medication is sometimes given by IV injection to further improve bowel distention.
Glucagon hydrochloride
What is the best position for a patient to lay in after a myelogram to avoid headache?
With their head elevated 30 degrees for 1-3 hours
When a patient who previously reacted to HOCM is given an LOCM for a subsequent study, what is the percentage of the patient having a repeat reaction?
5%
What is the basic functioning unit of the kidney?
The nephron
What is the concern of patients taking Metformin that receive IV contrast?
Renal dysfunction occurring in patients taking metformin can cause the drug to accumulate which may result in lactic acidosis.
What is a CVAD?
Central venous access device
What is the difference between a non-tunneled central catheter and a PICC?
The non-tunneled central lines are larger caliber and are designed to be inserted into a vein such as the subclavian, jugular, or less commonly the femoral vein.
What is a tunneled CVC and what are three types?
They are inserted into the vein by "tunneling" under the skin reducing risk of infection. Examples are Hickman, Broviac, and Groshong catheters.
What is AVID?
Arteriovenous Iodine Difference. The difference in HU of the aorta compared to the IVC
What is the AVID for the bolus phase?
30 HU difference between the aorta and IVC
What is the AVID during the nonequilibrium phase?
10-30 HU
What is the AVID during the equilibrium phase?
Less than 10 HU
What is another name for the venous phase?
Nonequilibrium
How long after the start of injection does it usually take for the aorta to reach peak enhancement?
15-22 seconds
Peak organ enhancement (e.g. pancreas, bowel, bladder) occurs within ___ to ___ seconds after peak aortic enhancement.
5 to 15
How much of the blood supply to the liver comes from the portal vein?
75%
How much of the blood supply to the liver comes from the hepatic artery?
25%
How long does it take for the portal venous phase of the liver following bolus injection?
60 seconds
What is the scan delay for a brain with contrast and why?
4 minutes or greater to allow time for contrast to break the blood brain barrier
On a time density graph, what represent the x and y axis?
x axis = time elapsed in seconds after the start of injection
y axis = enhancement level in HU
What is bolus shaping?
manipulating the flow rate during an injection to improve the likelihood of optimal vascular enhancement
What is the name of the technique used when there are two different flow rates used during the same bolus?
Biphasic
How are test bolus scans typically performed?
By injecting 10-20 mL of contrast, scanning with the lowest possible mA setting, at 2 second intervals, at the same slice location, for 20 to 30 seconds about 8 to 15 seconds after the start of the injection.
What is the formula used for the scan delay time based upon a test bolus?
trial scan delay + (2 x the image showing maximum enhancement) + 3 seconds
How much of a scan delay is required for a 64 detector row scanner to increase likelihood of peak arterial enhancement?
5-20 seconds
What type of catheter is recommended to be flushed with a heparin saline solution after their use?
Open ended CVAD catheter
An abdomen study with contrast injected at 3 mL/sec with a 60 second delay is interrupted, how long does the tech have to scan the patient before it is too late to get an optimal study?
30 - 40 seconds
For which type of study can a drip infusion be given?
Routine brain for a tumor
What is the maximum energy of ionizing radiation used in CT and the average energy?
Max: 120-140 keV
Average: 70 keV
What is the unit of x-ray exposure in air?
Roentgen (R)
What is the unit of absorbed dose? What is the SI unit of absorbed dose?
Radiation absorbed dose (rad)
Gray (Gy)
What is the amount of energy absorbed per unit mass at a specific point?
Radiation absorbed dose (rad)
How does a rad compare to the Gray?
100 rad = 1 Gy
This factor accounts for the different health effects produced from different types of ionizing radiation.
Quality factor (Q)
What is the quality factor for the diagnostic xrays that are used in CT?
1
When the quality factor has been applied to the radiation absorbed dose, the new quantity is the dose equivalent, expressed in units known as the:
Roentgen equivalent in man (rem)
What is the SI equivalent unit to the rem?
Sievert (Sv)
How does the rem equate to the Sievert?
100 rem = 1 Sv
What measurement tries to account for the effects particular to the patient's tissue that has absorbed the radiation?
Effective dose or effective dose equivalent. It is reported in Sv or rem.
The central dose for a body scan is approximately ______ of the peripheral dose.
1/3 to 1/2
The areas of scatter into adjacent tissue are called what?
Tails
Tails contribute approximately how much additional dose to the entire study?
25-40%
What is MSAD and what does it stand for?
Multiple scan average dose. It is the central slice radiation dose, plus the scatter overlap (or tails).
The _____ is what manufacturers roport to the FDA and prospective customers regarding the dose typically delivered for their machines.
CTDI (computed tomography dose index)
The CTDI can only be calculated if:
The slices are contiguous
If a gap exists between slices, the ______ is multiplied by the ratio of the slice thickness to slice increment which would give the _____.
CTDI, MSAD
The CTDI-100 is calculated using a dosmiter called a :
pencil ionization chamber
_____ is the preferred expression of radiation dose in CT dosimetry.
CTDI-vol
The skin dose of a CT abdomen compared to a KUB xray is ___ times higher. The absorbed dose is ____ times higher.
10 times, 100 times
Generally, the radiation doses to patients are about ___ % to ___ % greater with earlier models of MDCT.
30-50%