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CT & MRI > Week 1 > Flashcards

Week 1 Flashcards

1
Q

what % of radiation comes from CT

A

60%

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2
Q

difference between gen rad & CT

A

CT reconstructs cross sectional images of internal structures according to x-ray attenuation coefficients for almost every part of body

gen rad only makes 2d image where superimposition poses a potential issue in hiding key info

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3
Q

CT use examples

A
  1. diagnosis, monitoring, screening diseases
  2. image guided therapy such as target localization & treatment planning
  3. attenuation correction of radionuclide imaging & localization
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4
Q

similarity between CT & linear tomography

A

produces detailed images of specific layers of body

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5
Q

what does CT allow for

A
  • new clinical applications
  • decreased dose
  • iodinated contrast media
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6
Q

CT was previously known as

A

computerized axial tomography (CAT) scans

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7
Q

how does CT work

A

x-ray tube & detector rotate around patient to acquire data > processed by computer > reconstructs detailed slices of cross sectional anatomy of various body regions

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8
Q

what imaging technique was used to visualize brain before CT

A

radiography / pneumoencephalography

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9
Q

which mathematician introduced transformation operator that laid foundation for tomographic reconstruction

A

Johann Radon; radon & inverse radon transform

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10
Q

who validated Allan Cormack’s work by building 1st CT prototype

A

Sir Godfrey Hounsfield

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11
Q

which gen of CT scanner uses wide fan beam

A

3rd, 4th, 6th

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12
Q

which gen of CT scanner uses narrow fan beam

A

2nd

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13
Q

which gen of CT scanner uses cone beam

A

7th

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14
Q

which gen of CT scanner uses pencil beam

A

1st

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15
Q

which gen of CT scanner uses electron gun firing beam

A

5th

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16
Q

which gen of CT scanner uses translate-rotate

A

1st, 2nd

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17
Q

which gen of CT scanner uses rotate-rotate

A

3rd, 6th, 7th

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18
Q

which gen of CT scanner uses rotate-fixed

A

4th

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19
Q

which gen of CT scanner uses stationary-stationary

A

5th

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20
Q

which gen of CT scanner starts the use of helical/spiral

A

6th

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21
Q

what is slip ring indicative of which gen

A

3rd

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22
Q

purpose of pre-patient collimators

A
  • lower radiation dose
  • prevent over-beaming
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23
Q

purpose of post-patient collimators

A
  • reduce scatter & penumbra
  • defines slice thickness

SPS

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24
Q

purpose of slip-rings

A
  • allows scan frame to rotate continuously without stopping to rewind cables
  • power & control signals comms to rotating frame through slip ring
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25
Q

image formation process

A
  1. tube generates radiation
  2. radiation penetrates body & attenuated by tissue
  3. attenuated xray processed by detector
  4. detector converts radiation into electrical signals
  5. computer converts data into high res images
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26
Q

GOS

A

gadolinium oxysulfide

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27
Q

Pr

A

Praesodynium-doped

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28
Q

Lu

A

Lutetium

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29
Q

UFC

A

ultrafast ceramic

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30
Q

Gemstone Clarity Detector uses

A

Lu-based garnet

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31
Q

NanoPanel Prism Detector uses

A

Top layer: yttrium based garnet
bottom layer: GOS

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32
Q

Stellar Detector uses

A

UFC

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33
Q

Quantum Vi Detector uses

A

Pr GOS

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34
Q

PURE vision CT detector uses

A

Pr as an active additive of Toshiba GOS

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35
Q

commonly used solid state detectors

A

GOS, CsI, UFC

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36
Q

properties of solid state detectors

A

high detection, high geometric, small DELs

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37
Q

purpose of solid scintillator layer is to

A

convert x-ray photons to light photons

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38
Q

purpose of photodiode layer is to

A

convert light photons to electrical signal

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39
Q

purpose of beam shaping filter is to

A

remove low energy / soft x-rays to narrow x-ray energy spectrum and create monochromatic beam (beam hardening)

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40
Q

what happens if the patient is off iso-center

A

filtering mismatch > x-ray output needs to be compensated = increased dose

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41
Q

sequential scan

A

patient moves gradually layer-by-layer through gantry during scan

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42
Q

spiral scan

A

patient continuously moves through gantry during scan

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43
Q

advantages of using multi-row detectors

A
  • reduced scan time
  • less motion artifacts
  • shorter breath holds needed
  • multiphase contrast enhanced scanning possible
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44
Q

multi-slice CT benefits over single-slice CT

A
  • efficient use of x-ray beam with increasing slices
  • reduced dose
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45
Q

what configs do array detectors offer

A

fixed & adaptive array configs

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46
Q

pitch definition

A

table distance traveled in 1 360 degrees gantry rotation divided by beam collimation / x-ray beam width

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47
Q

typical detector pitch ranges from

A

0.75 - 1.5

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48
Q

choice of pitch influences __

A
  1. image quality
  2. patient dose
  3. scan time
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49
Q

helical scan is only used for

A

larger structures

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50
Q

what factors involved in ‘scan & data acquisition’

A

kVp, mA, scan time, Pitch, Beam Width, scan FOV (body coverage)

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51
Q

what factors involved in ‘image reconstruction’

A

slice thickness, FOV, matrix, filter

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52
Q

what factors involved in ‘display control’

A

zoom, window width, window level

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53
Q

Process for scan & data acquisition

A
  1. scout / topogram / localizer AP &/or lateral
  2. Plan CT scan region
  3. CT acquisition
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54
Q

SFOV

A

area within gantry that raw data is collected

55
Q

DFOV

A

determines how much of the SFOV is reconstructed into an image

56
Q

pitch less than 1 is used for

A

imaging small structures & highly detailed ones

57
Q

purpose of adjusting DFOV

A
  1. exclude unnecessary area from image
  2. focus on specific anatomical regions
  3. include more anatomical info in image
58
Q

pitch higher than 1 is used for

A

temporal structures & screening

59
Q

constant kVp used for CT is

A

120 / 130 kV

60
Q

when should you consider lowering kVp

A

to give more contrast esp with iodinated contrast & exploit k-edge

61
Q

what is the downside of lowering kVp

A

increased noise which can be compensated with increased mAs but leads to increased dose

62
Q

CT dose is approximately ___ of applied kVp

A

proportional to the square

63
Q

diff between kVp & keV

A

kVp = peak voltage applied to xray influencing max energy of xray photons produced

keV = energy of individual xray photons

64
Q

diff between average & max keV

A

avg = mean energy of xray photons in beam which influences image contrast & quality

max = highest energy of xray photons which indicates most penetrating photons

65
Q

why does iodine attenuation increase at lower tube potential

A

decreased compton scatter & increased photoelectric effect as photon energy approaches k-edge of iodine (33.2keV)

66
Q

if u want reconstructed images at a certain slice thickness, will you use a smaller or larger detector width to acquire raw data

A

wider anatomy = larger detector width = lower quality & dose

highly detailed anatomy = smaller detector width = higher quality & dose

67
Q

what happens before reconstruction

A

interpolation

68
Q

how does CT compensate this assumption of a circular path instead of a helical one

A

helical raw data set is interpolated into series of 2D image data sets before filtered back projection

69
Q

how is interpolation achieved

A

weighing helical data average from either side of reconstructed plane

70
Q

simple back projection is used to

A

emulate acquisition process in reverse

71
Q

what does each ray in each view represent

A

individual measurement of attenuation factor

72
Q

what is needed for simple back projection algorithm to regain image

A

take into account the position & angles of each detector

73
Q

assumptions for simple back projection

A
  1. infinitely small DELs
  2. monochromatic spectrum for determination of micro
  3. small FSS
74
Q

how does the computer store simple back projection

A

in sinograms

75
Q

what does the horizontal & vertical axis of simple back projection refer to

A

horizontal = different rays in each projection

vertical = projection angle

76
Q

vertical line on sinogram means

A

bad detector

77
Q

what is the issue of simple back projection

A

produces lots of blurring artifacts since assumptions are not met

78
Q

filtered back projections are used to

A

filter blurring artifacts, noise, low contrast using different filters that offer tradeoffs between spatial resolution & noise

79
Q

bone filter provides

A

fine details but noisy images

80
Q

soft tissue filter provides

A

smoothing but less noise & spatial resolution

81
Q

___ used to reconstruct CT images

A

iterative algorithms

82
Q

how does iterative algorithms work

A
  1. pulls out image assumption from vendor
  2. compares it to real time data while making constant adjustments
  3. repeats till both assumption & real data are in agreement
83
Q

iterative reconstruction advantages

A
  1. reduced noise
  2. increased CNR & spatial resolution
84
Q

iterative reconstruction disadvantages

A
  1. slow
  2. less predictive behavior
85
Q

process of mapping x-ray attenuation back to its original voxel is ___

A

back projection

86
Q

CTDIvol

A

Volume CT Dose Index

87
Q

CTDIvol unit

A

mGy

88
Q

DLP unit

A

mGy.cm

89
Q

absorbed dose formula

A

CTDIvol x DLP

90
Q

DLP

A

dose length product

91
Q

effective dose formula

A

DLP x conversion factor

92
Q

effective dose unit

A

Sv

93
Q

DLP formula

A

CTDIvol x CT length of scan range

94
Q

anything with Gy is __

A

absorbed dose

95
Q

anything with Sv is ___

A

effective dose

96
Q

deterministic risk primarily described by

A

CTDIvol

97
Q

stochastic risk described by

A

DLP & effective dose

98
Q

CTDI weighted formula

A

1/3 CTDI center + 2/3 CTDI peripheral

99
Q

____ values are used to describe radiation to patients

A

CTDI; not actual dose values

100
Q

CTDIvol formula

A

CTDIvol = CTDI weighted / pitch

101
Q

what does CTDIvol account for

A

effect of pitch on dose

102
Q

what does CTDI weighted account for

A

approximate average dose per slice

103
Q

DLP represents

A

total radiation energy deposited in patient’s body

104
Q

effective dose is used for

A

estimation of risks

105
Q

CT dose reduction strategies

A

DIMAR

  1. automatic tube current modulation (mA)
  2. reduce tube voltage in appropriate patients (kV)
  3. DRLs
  4. minimize scan ranging
  5. iterative reconstruction
106
Q

what are DRLs

A

surveys of dose estimates from diff modalities to highlight substantial variations in dose between diff facilities for same exam & similar patient group

107
Q

purpose of DRLs

A

monitoring practices to promote improvements in patient protection

108
Q

national & local DRLs set for

A
  1. each exam
  2. each clinical indication
  3. each patient group
109
Q

what CT DRLs are recommended quantities

A

CTDIvol & DLP

110
Q

DRLS are determined as

A

median values observed for representative samples of particular group of patients

111
Q

good CT images characteristics

A
  1. high spatial resolution
  2. high low contrast detail
  3. acceptable temporal resolution
  4. minimal noise
  5. no artifacts
112
Q

pixel size formula

A

DFOV / matrix size

113
Q

voxel size is dependent on

A
  1. FOV
  2. Matrix
  3. Slice thickness
114
Q

how is spatial resolution expressed

A

lp/mm , lp/cm

115
Q

how is spatial resolution measured

A

using resolution bar patterns

116
Q

what is important in 3D/MPR reconstruction

A

detector array thickness

117
Q

thinner slice thickness for spatial resolution leads to

A
  1. higher spatial resolution
  2. less partial volume effect
  3. lower contrast
  4. more noise
118
Q

thicker slice thickness for spatial resolution leads to

A
  1. more partial volume effect
119
Q

when dose partial volume effect occur

A

when object doesnt fill entire depth of scan plane which is dependent on slice thickness = CT number underestimated

120
Q

what does contrast refer to

A

sensitivity of the system; ability to differentiate between intensity differences in image

121
Q

how to improve contrast resolution

A
  1. reduce noise by increasing mAs & slice thickness (increased dose)
  2. lower tube voltage
  3. reconstruction algorithms
122
Q

what are the risks of too long scan time

A

breathing artifacts & motion artifacts which can lead to double contour of organs

123
Q

what is noise

A

quantum noise determined by x-ray flux & number of detected photons which is influenced by
1. detector efficiency
2. scanning technique
3. patient habitus

124
Q

the greater the noise, the ___ the SD

A

greater

125
Q

how to increase details in CT

A
  1. decrease slice thickness
  2. increase matrix
  3. decrease FOV
126
Q

why is patient preparation before Ct important for

A
  • optimal image quality
  • efficient workflow
  • safety
  • patient cooperation
127
Q

importance of checking clinical history & previous images

A

determines appropriateness of imaging choice & best protocol to do so

128
Q

helical CT allows for ___

A

rapid volumetric scanning; common among modern CTs

129
Q

Cine / Cardiac CT allows for ___

A

multiple rotations with/without cardiac gating

130
Q

CT perfusion allows for ___

A

multiple time points post processing to compute tissue dynamics

131
Q

4D lung planning allows for ___

A

multiple time phase reconstruction during respiratory cycles

132
Q

TZM means ___

A

titanium / zirconium / molybdenum

133
Q

what is afterglow

A

persistence of image after radiation has been turned off

CT & MRI (12 decks)

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