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MRT Year 2 > CAMRT Review: CT Theory > Flashcards

CAMRT Review: CT Theory Flashcards

1
Q

Limitations of 2D imaging?

A
  • Superimposition of structures
  • Difficult to distinguish slight density differences
  • Difficult to identify precise location of abnormalities
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2
Q

What is a focal plane?

A

Tomography term

“Section thickness”

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3
Q

What is the fulcrum?

A

Imaginary pivot point about which the x-ray tube and the IR move
“Dead center”

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4
Q

Blur is increased as distance from the focal plane _________?

A

Increases

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5
Q

Increased tomographic angle = _______ section thickness

A

Decreased

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6
Q

Advantages of tomography over general radiography?

A
  • Increased radiographic contrast
  • Increased subject contrast
  • Decreased superimposition
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7
Q

Disadvantages of tomography over general radiography?

A

-Increased patient dose

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8
Q

Basic principles of CT?: why do we use it over general radiography?

A
  • minimize superimposition

- improve contrast

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9
Q

Primary disadvantages of CT?

A
  • Increased radiation dose
  • Artifacts
  • Decreased spatial resolution
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10
Q

What is the scan point on the table?

A

-Can use to determine the location of a pathology

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11
Q

What is the scannable range of the table?

A

-How much area can be scanned without having to move the patient

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12
Q

What components are housed within the gantry?

A
  • Tube
  • Detector array
  • Generator
  • Filtration
  • Collimators
  • DAS
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13
Q

What is the aperture of the gantry? What is the isocenter?

A

The hole in the gantry that the patient moves through. The isocenter is the center of that hole

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14
Q

What is a CT x-ray tube designed for?

A

To dissipate heat

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15
Q

Is a glass or metal envelope better? Why?

A

Metal

  • prevents arcing
  • increases current
  • increases heat dissipation
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16
Q

What is different about CT anodes? What are they made out of?

A
  • Larger
  • Thicker
  • Smaller target angle
  • High rotation speeds
  • Rhenium, Tungsten, and Molybdenum
  • Graphite base
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17
Q

Types of filtration?

A
  • Added

- Inherent

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18
Q

What does filtration do?

A
  • Hardens beam: removes longer wave-length x-rays
  • Beam uniformity: more homogeneous
  • Decreases patient dose
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19
Q

Types of collimation schemes?

A
  • Source: before patient, dose profile

- Post-patient: keeps beam a slice not a fan

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20
Q

Hounsfield Units of water, air, bone, and metal?

A

Air: -1000
Water: 0
Bone: 1000
Metal: 2000

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21
Q

Why does CT use high kVps?

A
  • Decrease attenuation on coefficient : more penetration
  • Decrease contrast of bone to soft tissue: more scatter
  • Increase radiation flux at detector : more radiation to detector
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22
Q

2 types of gantry geometries?

A
  1. Continuous: detectors and tube rotate

2. Stationary: detectors stationary, tube rotates

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23
Q

What are scout images used for?

A
  • Planning the scan

- not considered data acquisition

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24
Q

2 methods of data acquisition?

A
  1. Axial

2. Helical

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25
Q

Another name for axial scans?

A

Conventional/serial

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26
Q

Advantages of axial scanning?

A
  • Slices perpendicular to patient
  • Acquisition can vary
  • Highest image quality
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27
Q

3 ways data can be acquired during an axial scan?

A
  1. Contiguous
  2. Gapped
  3. Overlapped
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28
Q

Disadvantages of axial scans?

A
  • Increased exam time
  • Scan delay: not good for scanning contrast filled vessels
  • Increased likelihood of motion artifacts
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29
Q

What enables helical scans?

A

Slip ring technology

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30
Q

Advantages of helical scanning?

A
  • Decreased scan time
  • Scans a volume of tissue
  • Reduces misregistration
  • More reformatting and reconstruction
  • Less contrast required
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31
Q

What type of data does image reconstruction use?

A

Raw data

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32
Q

What type of data does image reformatting use?

A

Image data

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33
Q

Disadvantage of helical scanning?

A

-Image quality is compromised: missing info: interpolation

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34
Q

4 types of data?

A
  1. Scan data
  2. Raw data
  3. Filtered raw data
  4. Image data
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35
Q

What is scan data?

A

Data that arise from the detectors

  • require preprocessing corrections before the image reconstruction phase can occur
  • prevents poor image quality
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36
Q

What is raw data?

A 
Preprocessed measurement (scan data) data
-can be stored and retrieved as needed
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37
Q

When does raw data turn into image data?

A

When it is reconstructed using algorithms

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38
Q

Reconstruction algorithms? (4)

A
  1. Back projection: data gets smeared
  2. Filtered back projection: removes blurring from smearing “convolved data”
  3. Fourier transform: used to reconstruct MRI
  4. Iterative Reconstruction: think automatic rescaling “makes image look better electronically”
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39
Q

Image reconstruction algorithms? (Changes the way raw data is manipulated to create image data)

A
  1. Standard: balance noise and detail
  2. Smoothing: soft tissue visualization, but decreases spatial res.
  3. Edge Enhancement: improved detail, but decreases contrast resolution
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40
Q

How does a CT image appear on a computer? How does it go from raw data to be displayed?

A

-Analog data is first converted to digital to assign HU, then it is converted back so that we can see it as tissue not numbers

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41
Q

Reformatting improved with _______ (thinner/thicker) slices?

A

Thinner

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42
Q

When do stair step artifacts occur?

A

When thick slices are used for reformatting

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43
Q

How is slice thickness controlled in SDCT?

A

It is determined by pre-patient collimators, can only be as wide as the detector, but can be narrower

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44
Q

How is slice thickness determined for MDCT?

A
  • pre patient collimator width

- detector configuration

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45
Q

What is volume averaging determined by?

A

Slice thickness
Thicker slice = more averaging
-increases likelihood that structured will be superimposed

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46
Q

What is retrospective slice incrementation? (Post-processing). Why is it useful?

A

Enables the operator to chance the slice center of an image

  • no increase in patient dose
  • can decrease partial volume effect
  • cannot change slice thickness in SDCT
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47
Q

Retrospective slice incrementation: can you make the slice smaller than the acquisition slice? Why/why not?

A

No.

-noise

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48
Q

What is pitch?

A

Ratio of the table movement per 1 gantry rotation to the slice thickness

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49
Q

Does pitch change slice thickness?

A

No, it just changes how much anatomy is in 1 slice

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50
Q

Advantages of increased pitch? (Less than 1.5)

A
  • decreased scan time: pt motion, holding breath
  • improved imaging of contrast filled vessels
  • decreased patient dose
  • decreased heat load
  • minimal loss of image sharpness
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51
Q

Pitch formula: SDCT

A

Pitch = table movement in 1 gantry rotation / slice thickness

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52
Q

Pitch formula: MDCT

A

Pitch = table movement per 1 gantry rotation / slice thickness x number of slices

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53
Q

Anatomy coverage formula: SCDT?

A

Pitch x total acquisition time x (1/rotation time) x slice thickness

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54
Q

Anatomy coverage formula: MDCT?

A

Pitch x total acquisition time x (1/rotation time) x slice thickness x number of slices

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55
Q

Increased matrix = _________ pixel size

A

Decreased pixel size

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56
Q

Decreased pixel size = __________ spatial resolution?

A

Increased

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57
Q

What is a voxel?

A

Volume of tissue

-isotropic = same dimensions all around, what we want

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58
Q

What is sampling when referring to pixels?

A

The pixel detects radiation throughout the entire scan and then averages it at the end to display a shade of grey

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59
Q

What is bit depth?

A

The amount of greys that a pixel can show

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60
Q

Where should the window level be set at for a scan?

A

Close to what the HU is of what you want to see

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61
Q

Increased WW = __________ contrast

A

Decreased, long scale contrast

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62
Q

When is long scale contrast good?

A

When there are many different densities to be seen

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63
Q

When is short scale contrast good?

A

When looking at similar densities

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64
Q

Decreased WL = __________ brightness

A

Increased brightness

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65
Q

What is the SFOV?

A

Scan field of view: determines the area within the gantry that the raw data will be acquired from

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66
Q

What is the DFOV?

A

Display field of view: determines how much of the acquired raw data will be used to create an image

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67
Q

Does DFOV change pixel size?

A

Yes

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68
Q

Decreased DFOV = _________ spatial resolution?

A

Increased

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69
Q

Is DFOV of magnifying better for spatial resolution?

A

Decreasing DFOV

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70
Q

What is the difference between analog and digital data?

A

Analog is continuous data

Digital is one value

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71
Q

Why is the table made out of carbon fibre?

A
  • strength
  • low absorption
  • vibrational properties
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72
Q

Advantages of the power injector?

A
  • volume, injection rate, and delay can be preprogrammed
  • protocols can be user defined and stored for injection consistency
  • injection pressure is monitored enabling administration precision
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73
Q

Limitations of the power injector?

A
  • kinked tubing
  • high viscosity
  • incompatible equipment
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74
Q

Miscentering of 3-6cm can result in an increase in dose of _____%?

A

18-41%

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75
Q

Miscentering in elevation by 20-60mm can result in a dose of up to ____%

A

140%

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76
Q

Major function of the DAS?

A

Data acquisition system: measures the # of photons that strike the detector (measures the electric signal that comes from the detectors and coverts it to digital)

  • ADC
  • sends signal to computer for recording
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77
Q

Detectors operate more consistently with a _________ beam?

A

Homogenous

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78
Q

What do collimators do?

A
  • decrease patient dose
  • decrease scatter reaching IR
  • controls slice thickness by shaping the x-ray beam
  • controls voxel length
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79
Q

What do the detectors do?

A

Measure the x-ray photon energy and convert it into an electric signal

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80
Q

Is a long and skinny detector or a short and wide detector better? Why?

A

Long and skinny because wider ones pick up more scatter

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81
Q

Smaller detector = ________ spatial resolution?

A

Increased

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82
Q

Detector characteristics? (4)

A
  1. DQE
  2. Stability
  3. Fast response time
  4. Wide dynamic range
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83
Q

What is DQE?

A

Detective quantum efficiency: how well a detector can capture, absorb and convert x-rays

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84
Q

What increases DQE?

A
  • Wider detector : increases surface area
  • Decreased spacing
  • Composition: high atomic #, high density, high thickness
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85
Q

What is detector stability?

A

How much can you take before you snap

-how much radiation can it take before it has to be recalculated

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86
Q

What is detector response time?

A

How quickly can a detector detect another photon?

-ready to detect another photon quickly after receiving one already

87
Q

What is detector dynamic range?

A
  • we want wide
  • variety of signals able to be detected
  • able to capture a wide range of photon energies and display them in a variety of electric signals
88
Q

Types of detectors?

A
  1. Ionization chamber xenon gas

2. Solid-state scintillation

89
Q

How does a xenon gas detector work?

A
  • Tungsten plate in between the chambers attract ions
  • The movement of the electrons causes an electric current proportional to the number of photons absorbed by the system
  • *Photons come in and hit the xenon gas and lose an electron that is attracted to the negative plate and the now positive ion is attracted to the positive plate
90
Q

Advantages and disadvantages of a xenon gas detector?

A 
Advantages?
-less expensive
-highly stable
-no afterglow
Disadvantages?
-needs to be under pressure
-lots of space
-loss of photons at aluminum casing (decreased DQE)
91
Q

How does a solid state/scintillation detector work?

A

-converts x-rays to light to electrical

92
Q

What do scintillation detectors require?

A

Amplifiers to beef up the signal to get it proportional to the x-ray energy

93
Q

MDCT detector configurations?

A
  1. Matrix array: same size, isotropic

2. Adaptive array: anisotropic, different sizes, larger further from center

94
Q

Do thin slices or thick slices take up more storage space?

A

Thin

95
Q

CT generations?

A

1st Gen: narrow pencil beam, no detector array, translate-rotate 180 degrees
2nd Gen: narrow fan beam, linear detector array, translate-rotate 180 degrees
3rd Gen: wide fan beam, rotate-rotate 360 degrees, curved detector array
4th Gen: wide fan beam, rotate-fixed 360 degrees, circular single row detector array
5th Gen: fan beam, stationary-stationary, used for cardiac in 1980s, decreased spatial res
6th Gen: dual source, fan beam, rotate-rotate, improved spatial resolution, cardiac imaging

96
Q

Which generation is most susceptible to scatter?

A

4th because of the circular detector array

97
Q

Other technical applications of CT?

A
  1. Cardiac imaging
  2. CT fluoroscopy
  3. CT Angiography
  4. CT screening
  5. CT simulation
98
Q

What is CT simulation?

A
  • used to determine the exact size, location, and shape of a tumor for treatment
  • patients skin marked for treatment
99
Q

How do CT simulators differ from conventional CT scanners?

A
  • larger gantry aperture
  • flat table top
  • software capable of creating a targeted treatment path
100
Q

Can CT simulation machine do conventional CT? Can conventional CT scanners do CT simulation?

A

CT simulation can do conventional CT, but not the other way around

101
Q

What are the 2 parts that make up radiopharmaceuticals?

A
  1. The drug portion: goes to the source

2. The radioactive isotope: so we can see it

102
Q

What is the most common tracer used in nuclear medicine?

A

Technetium 99M

103
Q

Contraindications for a nuclear medicine scan?

A
  • no barium for 48hrs
  • no previous NM tests within the last week
  • appropriate prep: fasting, stop meds
  • removed all attenuating artifacts (metal)
104
Q

During a NM scan, gamma radiation is emitted from the _______ and captured by the detector?

A

Patient

105
Q

During a skeletal NM scan, which parts of the body usually have increased uptake?

A
  • bladder
  • sternum
  • SI joints
106
Q

What is SPECT?

A

Single Proton Emission Computed Tomography

107
Q

What is PET?

A

Positron Emission Tomography

108
Q

Advantages of SPECT over PET?

A
  • requires less space and consumables
  • no cyclotron required
  • operating costs
  • no positron emission
109
Q

What is spatial resolution? How is it measured?

A

The ability of a scanner to display 2 different objects immediately adjacent to one another without blurring them together
-lp/mm

110
Q

Increased spatial frequency = ________ object size?

A

Decrease

111
Q

Decreased spatial frequency = __________ object size?

A

Increased

112
Q

What is the modulation transfer function?

A

The ratio between image accuracy in comparison to the actual object scanned
-scale of 0-1

113
Q

Increased MTF = __________ object size

A

Increased

114
Q

What is contrast resolution?

A

2 objects with very similar densities will look different rather than the same

115
Q

Is the relationship of spatial frequency and image size linear?

A

No

116
Q

What is the uncoupling effect?

A

Automatic rescaling: overexposures can still look great on digital

117
Q

What is automatic tube current modulation?

A

-adjusts mAs as you scan the patient

118
Q

Can automatic tube current fix quantum mottle?

A

No, it can only manipulate what its been given

119
Q

Typical kVp for adults and children?

A

Adults: 120-140kVp
Children: 80kVp

120
Q

Small filament = _________ penumbra = ______ detail

A

Small filament = decreased penumbra = increased detail

121
Q

Focal spot size only affect ____________?

A

Spatial resolution

122
Q

Quantum mottle = _________ contrast?

A

Decreased

123
Q

Increased SNR = _________ contrast

A

Increased contrast

124
Q

Increased slice thickness = ________ contrast

A

Decreased because of more averaging

125
Q

Increased slice thickness = ___________ SNR

A

Increased because thicker slices have more photons in them

126
Q

Decreased pixel size = ___________ contrast resolution

A

Decreased because it catches less photons

127
Q

Pixel size formula?

A

Pixel size = DFOV/matrix size

128
Q

The pixel should be ____ the size of the object being scanned?

A

1/2

129
Q

3 general appearance of artifacts on CT image?

A
  1. Streaks
  2. Ring/band
  3. Shading
130
Q

Types of artifacts?

A
  1. Beam hardening
  2. Partial Volume
  3. Motion
  4. Metallic
  5. Out-of-field
  6. Cone beam
  7. Rings and Bands
  8. Noise
131
Q

Beam hardening artifact?

A
  • Caused by natural filtration of the x-ray beam by the object
  • Shading/streaks/
  • select appropriate SFOV or use beam hardening reducing software to avoid
132
Q

Partial volume artifact?

A
  • Caused by more than 1 type of tissue contained in a pixel
  • Shading
  • Use smaller pixels and thinner slices to avoid
133
Q

Motion artifacts?

A
  • Caused by: voluntary or involuntary motion
  • Shading, streaking, or blurring
  • Short scan times, sedation, immobilization, communication, software correction and cardiac gating to avoid
134
Q

Metallic artifacts?

A
  • Caused by the density of the metal
  • streaks
  • Improved HU range, proper changing instructions, high kVp, thinner slices
135
Q

Out of field artifacts?

A
  • Caused by: anatomy that extends out of the SFOV
  • streaks/shading
  • move arms out of way, increased size of SFOV to avoid
136
Q

Cone beam artifacts?

A
  • Cause by interpolation of data
  • streaks/shading near areas with large density differences
  • ONLY IN MDCT*
  • use lower pitch, cone beam reconstruction algorithms
137
Q

Ring and Band artifacts?

A
  • appear from malfunctioning or miscalibrated detector elements
  • rings/bands
  • unique to 3rd gen CT
  • recalibrate scanner, call service engineer
138
Q

3 types of noise artifacts?

A
  1. Quantum noise: scanner efficiency, patient size
  2. Inherent Physical Limitations: electronic noise in the DAS
  3. Reconstruction Parameters: high res reconstruction algorithms increase noise
139
Q

How to reduce noise artifacts?

A
  • increased mAs
  • low noise DAS
  • smoothing algorithms
140
Q

3 main categories of post-processing for CT?

A
  1. Basic functions
  2. Retrospective reconstruction
  3. Reformatting
141
Q

Type of 2D reformatting?

A

-MPR: formatting the image data into different planes that the one it was taken in

142
Q

Types of 3D reformats?

A
  • MIP :max intensity projection
  • MinIP: minimum intensity
  • SR: surface rendering
  • VR: volume rendering
143
Q

What is MIP?

A

Maximum Intensity Projection

  • pixels show the highest value detected and eliminate other values
  • high attenuation structures visualized
144
Q

What is MinIP?

A

Minimum Intensity Projection

  • pixels show the minimum values detected and eliminate other values
  • low attenuating structures
145
Q

What is SR? How does it work?

A
  • predetermined threshold
  • if the CT number is within the threshold, it is shown, if not, it is eliminated
  • we see the shell of an object
  • if threshold is too low: structures can be excluded
  • if threshold is too high (large): other materials that we don’t want to see might be included
  • only 10% of voxels contribute to image
146
Q

What is VR? How does it work?

A
  • all voxels contribute to image

- 3D semi-transparent representation of an object

147
Q

What is segmentation?

A
  • ROI editing
  • removed or isolates structures on an image for better demonstration of an area of interest
  • automatic or manual
148
Q

Forms of contrast media?

A
  • Liquid
  • Powder/paste
  • Gas
149
Q

Types of contrast we use?

A
  • Air
  • C02
  • Water
  • Barium sulfate
  • Iodinated water soluble
150
Q

Purpose of air and gas?

A
  • distention

- increase contrast

151
Q

Is spastic colon more likely to happen with air or C02?

A

Air

152
Q

How can air/gas be administered?

A
  • Injection
  • Orally
  • Rectally
153
Q

Cons of using water as a contrast media?

A
  • fast transit time/absorption

- poor bowel distention

154
Q

How can water be administered?

A

-orally

155
Q

Barium sulfate concentration for CT?

A

1-3%

156
Q

2 forms of barium sulfate?

A

Liquid: low concentration and viscosity
Paste: high concentration and viscosity

157
Q

Routes of administration of barium sulfate?

A
  • orally

- rectally

158
Q

What is VoLumen? Why is it used?

A
  • 0.1% barium sulfate solution
  • HU: 15-30 (less than mucosal lining)
  • resembles water on image, but increases bowel distention, transit time, and visualization of mucosa and bowel wall
159
Q

Iodinated water soluble contrast media routes of administration?

A
  • orally
  • rectally
  • injection: IV
160
Q

What can we inject intrathecally?

A
  • air
  • gas
  • iodinated water soluble
161
Q

3 methods of IV administration from least used to most commonly used in CT?

A
  1. Drip infusion
  2. Hand bolus
  3. Mechanical Injection
162
Q

What vein is preferred when establishing a line in the CT department?

A

AC vein

163
Q

What is the minimum amount of saline flushed to verify the patency of the line?

A

10ml

164
Q

Mechanical injector components?

A
  • Warming Device
  • Syringes
  • Pressure mechanism
  • Control panel
165
Q

3 phases in order from first to enhance to last to enhance?

A
  • Arterial (bolus)
  • Non-equilibrium (venous)
  • Equilibrium (delayed)
166
Q

Peak enhancement of arterial organs occurs ______seconds after the injection?

A

15-45

167
Q

Which organ requires a scan delay of 4 mins or longer. Why?

A

The brain because of the blood brain barrier

168
Q

When does each phase occur?

A
  1. Arterial (bolus): immediately after injection, 15-22secs
  2. Non-Equilibrium (venous): 1 min after bolus phase
  3. Equilibrium (delayed): 2 mins after bolus phase
169
Q

What do we see during the delayed phase?

A

Organ parenchyma

170
Q

What is the worst phase for liver scans?

A

Delayed

171
Q

Portal venous scans of the liver should occur ____ seconds after the bolus injection to include the arterial and venous enhancement?

A

60 seconds

172
Q

Peak enhancement for the kidneys is ______ seconds after the bolus injection because they also excrete contrast?

A

80-120 seconds

173
Q

The timing of the 3 phases is controlled by what 3 things?

A
  1. Pharmacokinetics
  2. Patient factors
  3. Equipment
174
Q

Increased volume = ________ magnitude of peak enhancement?

A

Increased

175
Q

Increased volume = _______ time to peak?

A

Increased

176
Q

Increased volume = ________ time a given level of enhancement is maintained?

A

Increased

177
Q

Total volume of contrast formula?

A

V- (ml/sec)(sec)

178
Q

Optimal imaging occurs at ____HU?

A

200

179
Q

Increased flow rate = ________ magnitude of peak enhancement?

A

Increased

180
Q

Increased flow rate = _______ time to peak enhancement?

A

Decreased

181
Q

Increased flow rate = _________ duration of contrast injection?

A

Decreased

182
Q

Increased weight = _________ magnitude of peak enhancement?

A

Decreased

183
Q

Increased weight = __________ time to peak

A

No effect

184
Q

Increased heart rate = __________ magnitude of peak?

A

No effect

185
Q

2 automated triggering methods?

A
  1. Test bolus: 10-15 images taken at same anatomic location, gives you the time at which you should start the real scan
  2. Bolus triggering: when HU threshold is reached, injection starts
186
Q

The level of risk associated with a CT exam is considered acceptable if?

A
  • the patient is aware of the risk
  • the patient receives some type of benefit
  • ALARA is maintained to reduce risk
187
Q

What is absorbed dose? What is it measured in?

A

The amount of energy absorbed per unit mass of material

-grays (Gy)

188
Q

What is effective dose?

A

Attempts to account for the effects specific to the patient’s tissue that absorbed the radiation dose

189
Q

2 main classifications of radiation effects?

A
  • Stochastic: no threshold, late effects, cancer, hereditary effects
  • Deterministic: threshold, early effects
190
Q

Max dose limit for canadian radiation workers?

A

20mSv whole body

191
Q

Early- non-stochastic effects? (3)

A
  • skin erythema
  • epilation
  • pericarditis
192
Q

In CT, which dose is greater: the entrance skin dose, or dose at the center of the patient?

A

Entrance dose

193
Q

What is the partial shielding effect?

A

The dose at the periphery of the patient is higher than that of the middle of the patient (organs absorb/block) the radiation as it goes through the patient

194
Q

Are organ doses higher for thinner or thicker patients?

A

Thinner, because less partial shielding

195
Q

What is over-ranging?

A

Exposed scan length is greater than planned scan length

-occurs in helical scans

196
Q

Decreased SFOV = ____________dose?

A

Increased because smaller patients have a more uniform dose distribution which means a higher total dose (entrance + exit radiation)

197
Q

Decreased slice thickness = _________ patient dose?

A

Increased because you must increase technique or else there is too much noise

198
Q

3 cardinal rules of radiation protection?

A
  1. Time
  2. Distance
  3. Shielding
199
Q

CT shielding?

A
  1. In-plane (bismuth): don’t use during scout, in the image
  2. Out of plane (lead): must be wrapped 360 deg around patient, reduces scatter
  3. Secondary: room walls due to scatter
200
Q

A 1yr old is _____ times more likely than a 50yr old to get cancer when the same dose is used?

A

6 times

201
Q

What is a DRL? What is their purpose?

A

Diagnostic Reference Level

  • promote better control of patient exposures to x-rays
  • identifies acceptable limits for an exam
202
Q

What does dosimetry allow?

A

-techs to compare their doses with a national average

203
Q

What dosimeter is the easiest method for recording exposure in CT?

A

Ionization chamber

204
Q

What do dosimetry phantoms measure?

A

CTDI (computed tomography dose index)

205
Q

3 CT dose measurements that we should be aware of and their units of measurement

A
  1. CTDI: grays (Gy): dose of 1 slice
  2. DLP: dose length product: mGy/cm: dose of entire scan
  3. ED: effective dose: sieverts (Sv)
206
Q

What dose measurement allows dose to be compared between scanners?

A

CTDI

207
Q

Does CTDI work for helical scans?

A

No, we must estimate for helical scans as this only works with contiguous slices

208
Q

Does CTDI include scatter in dose?

A

Yes

209
Q

Types of CTDI measurements? (4)

A
  1. CTDI(fda): index that relates to # of slices and slice width used
  2. CTDI(100): modification to accommodate smaller slice widths
  3. CTDI(w): dose in the x-y axis to accommodate dose uniformity
  4. CTDI(volume): dose in the z-axis (slice thickness)
210
Q

CTDI volume formula?

A

CTDI(volume) = CTDI(w)/pitch

211
Q

DLP formula?

A

DLP = CTDI(volume) x scan length

212
Q

______ (dose measurement) is directly proportional to scan length?

A

DLP

213
Q

ED formula?

A

ED = DLP x K (factor always given)

MRT Year 2 (18 decks)

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