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Laura Nappi online course > Computed Tomography (CT) > Flashcards

Computed Tomography (CT) Flashcards

1
Q

computed tomography (CT) is also called _______ tomography

A

axial

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2
Q

CT images are of what plane?

A

-axial
-transaxial
-transverse
-acquired in the plane perpendicular to long axis of body

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3
Q

“tomos” is Greek for –

A

cutting

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4
Q

what axis represents LENGTH of patient?

A

Z axis!

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5
Q

what axis represents WIDTH of patient?

A

X axis!

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6
Q

what axis represents HEIGHT of patient?

A

Y axis!

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7
Q

Z axis is length of patient which splits them into –>

A

sup/inf

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8
Q

X axis is width of patient which splits them into –>

A

rt/lt lats

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9
Q

Y axis is height of patient which splits them into –>

A

ant/post

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10
Q

label the planes -
X, Y, Z

A

A = Z
B = X
C = Y

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11
Q

what is the gantry of CT?

A

the hole/donut

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12
Q

the CT gantry ranges from ____-____ cm

A

70-90 cm

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13
Q

CT scanner gantries __do/do not___ have the ability to tilt forward and backward

A

they do

-however, for CT sims we obvi don’t want this function

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14
Q

where are control panels located in CT room?

A

on CT gantry

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15
Q

what can you control with control panels in CT room on gantry?

A

-laser alignment
-gantry tilt
-table movement
-also houses mic and speaker

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16
Q

what are the major parts of CT? (7)

A
  1. slip rings
  2. generator
  3. cooling system
  4. xray source
  5. filtration system
  6. collimation
  7. detectors
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17
Q

describe CT slip rings -

A

slip rings are electromechanical devices with brush like apparatus

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18
Q

______ allow for continuous electrical power, electronic communication, and help the gantry rotate continuously

A

slip rings

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19
Q

_________ make helical CT scans possible

A

slip rings

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20
Q

_____ part of CT helps allow for higher energy and power of machine

A

generator

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21
Q

the CT generator produces what and how much energy? ___-___

A

120-140 kV
kilovolts

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22
Q

the ________ of CT keeps it’s temperature regulated

A

cooling system

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23
Q

the CT xray source has an anode focal spot of what size?

A

.5-1 mm

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24
Q

describe xray source of CT -

A

same rotating anode as LINAC with tungsten target as well

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25
Q

______ part of CT reduces range, and thus dose, of xrays reaching the patient

A

filtration system

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26
Q

how does the filtration system of CT reduce dose to patient?

A

by cleaning up lower dose xrays that wouldn’t help the image

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27
Q

the filtration system helps
1. create a more ______ beam
2. reduce _____
3. improve overall CT ____

A
  1. uniform
  2. artifact
  3. image
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28
Q

______ filter is typical filter used for head to reduce intensity to periphery of what we are imaging

A

bowtie filter

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29
Q

the following is what type of filter? -

A

bowtie filter in CT

-bowtie filter was on IX LINAC too

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30
Q

________ restricts xray beams to a specific area

A

collimation

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31
Q

_____ controls slice thickness and reduces ____

A
  1. collimation
  2. scatter
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32
Q

less scatter, better the image _____

A

contrast

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33
Q

how does collimation control slice thickness?

A

by narrowing or widening the xray beam

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34
Q

what is common CT slice thickness range?

A

.5 - 1 cm

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35
Q

________ are what collect information to create the image

A

detectors

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36
Q

multiple detectors collectively are called what?

A

detector array

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37
Q

how are detectors placed?

A

as close together as possible

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38
Q

what shape do detectors make when placed in CT gantry?

A

arc or full circle

arc = 3rd gen
full 360 = 4th gen

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39
Q

what are CT detectors made of?

A

solid-state crystal –> scintillation detectors

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40
Q

___larger/smaller___ detectors have better spatial resolution

A

smaller

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41
Q

describe differences in 3rd and 4th gen CTs -

A

3rd gen =
-detectors in arc shape
-the xray tube and detector array go around 360
-fan beam from xray tube
-single row detectors

4th gen =
-full circle of stationary detector arrays and one xray tube that goes around the 360
-fan beam from xray tube
-single row detectors

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42
Q

newer CTs (past 4th gen) have single row detectors or multidetector rows?

A

newer CT models have multidetector rows

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43
Q

describe differences between single row detectors and multidetector rows

A

single row =
-3rd & 4th gen
-700 - 4800 detectors in a single row arranged in arc or complete circle
-limits the upper limit of slice thickness (max 10 mm)
-one gantry rotation = 1 single slice

multidetector row =
-newer CTs
-4 - 64 parallel rows
- a single rotation can produce multiple slices
- increased scan speed

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44
Q

the introduction of __________ for newer CTs has increased scan speed

A

multidetector rows

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45
Q

single detector row CTs have about how many detectors? what about multidetector row CTs?

A

700 - 4800 detectors in a single row arranged in arc or complete circle

whereas multidetector rows have about 4-64 parallel rows

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46
Q

how many gantry rotations does it take to make 1 single slice for single row detectors CTs?

A

1 gantry rotation = 1 slice

whereas multidetector row CTs can make multiple slices in just one gantry rotation

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47
Q

single row detectors have an upper slice thickness limit of _____

A

max 10 mm

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48
Q

CT scanning is done in ___ scanning

A

helical

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49
Q

what are other names for helical scanning?

A

-spiral
-continuous acquistion

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50
Q

____ scanning increases scan speed and improves image resolution

A

helical

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51
Q

what was the OLD way of CT scanning?
-nowadays = helical scanning

A

used to be axial scanning –>
so similar process to step n’ shoot
-took too long

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52
Q

Pitch of CT scanning means/effects what?

A

pitch of CT is the relationship between couch movement and xray beam collimation

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53
Q

CT pitch is expressed how?

A

as a ratio

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54
Q

CT pitch ratio ranges from ___-____

A

.5:1 to 2:1

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55
Q

a CT pitch of .5:1 means what?

how about CT pitch of 2:1 -

A

.5:1 CT pitch = overlap and increased patient dose

2:1 CT pitch = extends the image & less patient dose

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56
Q

a __lower/higher___ pitch will increase scan speed

A

higher pitch will increase scan speed

–2:1 CT pitch = extends the image & less patient dose
–spread out spirals VS tight spirals that will take a longer time to accumulate

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57
Q

CT pitch and CT scan speed become very important for what type of patients?

A

breath hold patients

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58
Q

what are the 2 types of CT Scanning Data Types?

A

raw data and image data

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59
Q

describe the difference between raw data and image data -

A

raw data = what is acquired from scan

image data = what we can see and use for planning system

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60
Q

what type of data is acquired by system during scan?

A

raw data
– ie. scan data

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61
Q

raw data/scan data is sent where? to be turned into an image

A

sent to computer where it is turned into an image

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62
Q

____ data includes measurements obtained by detector array

A

raw data

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63
Q

____ data is used to create a variety of images

A

raw data

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64
Q

____ data = the processed raw data that is turned into an image

A

image data

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65
Q

for image data, the computer assigns ____ value to each pixel

A

HU (Hounsfield Unit)

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66
Q

for image data, the computer assigns an HU value to each ____

A

pixel

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67
Q

pixels represent what?

A

patient tissue

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68
Q

SFOV =

A

Scan Field Of View

69
Q

______ determines the area within the CT gantry that raw data will be acquired

A

SFOV
Scan Field Of View

70
Q

CT scan data is acquired in a ______ around the isocenter

A

circle

71
Q

Scan Field Of View can also be called what?

A

calibration field of view

72
Q

ex. if a 25 cm SFOV is selected, what is the diameter of the circle scan data/circle imaged going to be?

A

25 cm

73
Q

if a patient is larger, or we want more anatomy what may be do to SFOV?

A

extend the SFOV

74
Q

how many HU are there?

A

2000

75
Q

what is HU of air, water, bone

A

-1000 = air
0 = water
1000 = bone

76
Q

what would have an HU of 2000?

A

metal

77
Q

what is considered baseline HU?

A

water at 0

78
Q

monitors can only display how many shades of gray?

human eyes can only detect how many shades of gray?

A

monitor can display 256 shades of gray

and our eyes can only detect 40 shades of gray

79
Q

describe difference between Window Width (WW) and Window Level (WL) -

A

WW = range of shades of gray; determines # of HU represented on an image

WL = median; window center; selects center CT value of WW

80
Q

Window Width or Window Level affect brightness the most

A

WL (window level)

81
Q

Window Width or Window Level affect contrast the most

A

Window Width (WW)

82
Q

Window Width or Window Level increase/decrease the shades of gray of an image

A

WW (Window Width)

83
Q

increasing or widening Window _____means more numbers/shades of gray are available

A

Window Width

84
Q

__more/less__ shades of gray will decrease our image contrast

A

more gray !

– more shades of gray between stark black and stark white DECREASE contrast !

85
Q

the following are other names for what term?

–> scout, surview, topogram, scanogram, preview, pilot

A

localizer scans

86
Q

most CT scans begin w/ one or more ___ images

A

localizer

–scouts

87
Q

scout images/localizer images are used for what?

A

to select the region of interest to be scanned (ie. SFOV)!

88
Q

localizer scans/scouts are NOT axial scans!! they are what?

A

AP or lateral

89
Q

region of interest to be scanned is also known as the _____

A

SFOV

90
Q

localizer scans/scouts ensure anatomy is in ______ of imaging system

A

range

91
Q

not having the patient centered on CT can lead to what?

A

artifacts and clipping

92
Q

___________ estimates values between known values

A

interpolation algorithms

93
Q

what makes RECONSTRUCTION possible?

A

interpolation algorithms

94
Q

axial scans are reconstructed to _____ and ___ views

A

sagittal and coronal views!

95
Q

without interpolation, what would happen to the reconstructed coronal and sagittal views?

A

they would be blurry!

96
Q

label the planes -
-coronal
-sagittal
-transverse

A

blue = transverse
yellow = coronal
pink = sagittal

97
Q

which corresponds to Window Width, which for Window Level

A

A = Window Width
B = Window Level

98
Q

which corresponds to a .5:1 pitch?
which is 2:1 pitch example?

A

A = .5:1

B = 2:1

99
Q

which corresponds to Gen 3 CT and which is a Gen 4 CT?

A

A = gen 3
B = gen 4

100
Q

lower the HU value __darker/lighter___ the image

A

darker

101
Q

higher the HU value __darker/lighter__ the image

A

lighter/whiter

102
Q

T/F
localizer scans/scouts are NOT cross sectional scans

A

true

103
Q

localizer scans/scouts are acquired when the tube is ___stationary/not stationary___

A

stationary !!!

104
Q

the _____ image is used to select region of interest to be scanned/SFOV

A

scout

105
Q

what estimates the value between known values and makes reconstruction possible?

A

Interpolation Algorithms

106
Q

axial scans are reconstructed to ________ and __________ views?

A

coronal and sagittal views

107
Q

CT images are a display of many small pixels with different shades of gray depending on the _______ rate

A

attenuation rate (ie. HU)

108
Q

define “matrix”

A

the layout of cells (pixels) in rows and columns

109
Q

define “pixel”

A

picture elements; pixels are each cell within a matrix; 2D representation

110
Q

define “voxel”

A

volume element; 3D representation of tissue

111
Q

a voxel is a _____ representation of tissue, whereas a pixel is a _____ representation

A

voxel = 3D
pixel = 2D

112
Q

(pixel) x (__________) = VOXEL

A

pixel x slice thickness = voxel

113
Q

bigger matrix sizes have more pixels, this leads to a ___better/worse___ image

A

better

114
Q

what is the matrix size of CT scanner?

A

512 x 512 pixels

115
Q

what measures the relative linear attenuation coefficient of tissue?

A

pixels

116
Q

Hounsfield Units (HU) are also called what?

A

CT numbers

117
Q

_____ represent tissue density

A

HU - Hounsfield Units (also can be called CT numbers)

118
Q

what is the HU/CT # of water?

A

0

119
Q

what is the HU/CT # of air?

A

-1000

120
Q

what is the HU/CT # of bone?

A

1000

121
Q

what is the HU/CT # of muscle?

A

50

122
Q

what is the HU/CT # of blood?

A

ranges from 30-45

123
Q

what is the HU/CT # of CSF?

A

15

124
Q

what is the HU/CT # of fat?

A

ranges from -50 to -100

125
Q

what is the HU/CT # of lung?

A

ranges from -400 to -600

126
Q

if the HU/CT # is greater than 1000, what is the likely material/tissue?

A

metal

127
Q

what are differences between CT simulation machines and regular CT machines? *key word = simulation

A

CT sim = flat table top (also usually carbon fiber), larger bore, external lasers, immobilization device friendly table, virtual sim software that can generate BEVs and DRRs

128
Q

where are the external lasers in a CT sim room?

A

mounted on side walls/sides and ceiling/above

129
Q

external lasers are how far apart from interal lasers?

A

500mm or 50 cm

130
Q

are external lasers moveable? YES or NO
—if yes, then in what directions?

A

YES!
our external lasers move in the sag (x) (ceiling) (lt/rt) and vert (y) (lateral walls) (ant/post)

131
Q

concept check: do the internal lasers go anywhere for CT sim?

A

no - they are just not used. they stay in CT bore since they are fixed position lasers!

132
Q

is there sup/inf external lasers for CT sim? Why or Why not

A

no sup/inf laser usage for CT sim… we just move the table

133
Q

what is the point of external lasers for CT sim?

A

the point of ext lasers for sim is to be able to mark the patient/isocenter outside of the CT bore

134
Q

the higher contrast and higher resolution that we see on our DRRs is achieved how?

A

with smaller slice thicknesses and smaller spacing
…and adjusting mA - quantity of slices

135
Q

slice thickness is adjusted where?

A

in the gantry of the CT using collimation

136
Q

thinner slices have ___higher/lower___ image quality? and why

A

HIGHER quality due to reduced scatter

SBRT/SRS uses this technique

137
Q

thinner CT slices are achieved how?

A

through more collimation that narrows the xray beam

138
Q

one CT slice delivers about how much dose to patient?

A

1-6 Gy to skin surface

139
Q

a tighter pitch leads to what?

A

increased patient dose!

recall: .5:1 ratio = overlap

140
Q

what should CT spacing typically be?

A

< 5 mm

141
Q

what happens when there is MORE space between each CT slice?

A

there is less info obtained, so, the scan then has to interpolate more to fill in the gaps

142
Q

DRR is calculated from the _______

A

CT scan

143
Q

what does DRR stand for?

A

Digitally Reconstructed Radiograph

144
Q

DRRs are 2D or 3D representation of patient?

A

2D

145
Q

on trt machine, we know we are looking at a DRR when we see what?

A

scan with inclusion of MLCs or blocks

146
Q

DRRs are 2D images that show _______

A

treatment ports

147
Q

we use DRRs to match ____ images

A

port images

148
Q

kVp = _________

A

BEAM QUALITY

149
Q

mA = _________

A

BEAM QUANTITY

150
Q

as mA increases, patient dose ____decreases/increases_____

A

increases

151
Q

NEMA stands for what?
*hint - it is an Association

A

National Electrical Manufacturers Association

152
Q

ACR stands for what?

A

American College of Radiology

153
Q

a virtual simulation is performed when?

A

after CT sim is complete

154
Q

during a _____ simulation is when outlining of external contours, contours the target volumes, and OARs takes place

A

virtual

155
Q

T/F: virtual simulation displays ports/beams

A

true

156
Q

during a _____ simulation is when review of the plan and isodose distribution takes place

A

virtual

157
Q

RV stood for what (this was on a class exam)

A

Record & Verify system

158
Q

what does PACS stand for?

A

Picture Archiving and Communication System

159
Q

what does DICOM stand for?

A

Digital Imaging and Communication in Medicine

160
Q

the following is describing PACS or DICOM -

-allows for acquisition, interpolation, and storage of digital images

A

PACS

161
Q

the following is describing PACS or DICOM -

-creates standards for transferring images and radiographic information
-standards are created for sharing images

A

DICOM

162
Q

the standards for DICOM are produced by a joint committee of who?

A

NEMA and ACR

163
Q

what are the 4 main principles of PACS?

A
  1. image acquisition
  2. display system
  3. network
  4. storage system
164
Q

label the CT scan -

–green
–purple
–orange

A

–green = voxel
–purple = pixel
–orange = matrix

165
Q

Slice thickness can affect _______

A

quality

166
Q

smaller slices = _________ quality

A

higher

167
Q

increase kvp by ___% = doubles the mas

A

15%

168
Q

increasing mas, ___increases/decreases___ patient dose … and increasing kvp __does/does not____ increase patient dose

A

increase in mas - increases patient dose… and increasing kvp does not increases patient dose

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