Computed Tomography (CT) Flashcards
1
Q
computed tomography (CT) is also called _______ tomography
A
axial
2
Q
CT images are of what plane?
A
-axial
-transaxial
-transverse
-acquired in the plane perpendicular to long axis of body
3
Q
“tomos” is Greek for –
A
cutting
4
Q
what axis represents LENGTH of patient?
A
Z axis!
5
Q
what axis represents WIDTH of patient?
A
X axis!
6
Q
what axis represents HEIGHT of patient?
A
Y axis!
7
Q
Z axis is length of patient which splits them into –>
A
sup/inf
8
Q
X axis is width of patient which splits them into –>
A
rt/lt lats
9
Q
Y axis is height of patient which splits them into –>
A
ant/post
10
Q
label the planes -
X, Y, Z
A
A = Z
B = X
C = Y
11
Q
what is the gantry of CT?
A
the hole/donut
12
Q
the CT gantry ranges from ____-____ cm
A
70-90 cm
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
14
Q
where are control panels located in CT room?
A
on CT gantry
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
16
Q
what are the major parts of CT? (7)
A
- slip rings
- generator
- cooling system
- xray source
- filtration system
- collimation
- detectors
17
Q
describe CT slip rings -
A
slip rings are electromechanical devices with brush like apparatus
18
Q
______ allow for continuous electrical power, electronic communication, and help the gantry rotate continuously
A
slip rings
19
Q
_________ make helical CT scans possible
A
slip rings
20
Q
_____ part of CT helps allow for higher energy and power of machine
A
generator
21
Q
the CT generator produces what and how much energy? ___-___
A
120-140 kV
kilovolts
22
Q
the ________ of CT keeps it’s temperature regulated
A
cooling system
23
Q
the CT xray source has an anode focal spot of what size?
A
.5-1 mm
24
Q
describe xray source of CT -
A
same rotating anode as LINAC with tungsten target as well
25
______ part of CT reduces range, and thus dose, of xrays reaching the patient
filtration system
26
how does the filtration system of CT reduce dose to patient?
by cleaning up lower dose xrays that wouldn't help the image
27
the filtration system helps
1. create a more ______ beam
2. reduce _____
3. improve overall CT ____
1. uniform
2. artifact
3. image
28
______ filter is typical filter used for head to reduce intensity to periphery of what we are imaging
bowtie filter
29
the following is what type of filter? -
bowtie filter in CT
-bowtie filter was on IX LINAC too
30
________ restricts xray beams to a specific area
collimation
31
_____ controls slice thickness and reduces ____
1. collimation
2. scatter
32
less scatter, better the image _____
contrast
33
how does collimation control slice thickness?
by narrowing or widening the xray beam
34
what is common CT slice thickness range?
.5 - 1 cm
35
________ are what collect information to create the image
detectors
36
multiple detectors collectively are called what?
detector array
37
how are detectors placed?
as close together as possible
38
what shape do detectors make when placed in CT gantry?
arc or full circle
arc = 3rd gen
full 360 = 4th gen
39
what are CT detectors made of?
solid-state crystal --> scintillation detectors
40
___larger/smaller___ detectors have better spatial resolution
smaller
41
describe differences in 3rd and 4th gen CTs -
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
42
newer CTs (past 4th gen) have single row detectors or multidetector rows?
newer CT models have multidetector rows
43
describe differences between single row detectors and multidetector rows
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
44
the introduction of __________ for newer CTs has increased scan speed
multidetector rows
45
single detector row CTs have about how many detectors? what about multidetector row CTs?
700 - 4800 detectors in a single row arranged in arc or complete circle
whereas multidetector rows have about 4-64 parallel rows
46
how many gantry rotations does it take to make 1 single slice for single row detectors CTs?
1 gantry rotation = 1 slice
whereas multidetector row CTs can make multiple slices in just one gantry rotation
47
single row detectors have an upper slice thickness limit of _____
max 10 mm
48
CT scanning is done in ___ scanning
helical
49
what are other names for helical scanning?
-spiral
-continuous acquistion
50
____ scanning increases scan speed and improves image resolution
helical
51
what was the OLD way of CT scanning?
-nowadays = helical scanning
used to be axial scanning -->
so similar process to step n' shoot
-took too long
52
Pitch of CT scanning means/effects what?
pitch of CT is the relationship between couch movement and xray beam collimation
53
CT pitch is expressed how?
as a ratio
54
CT pitch ratio ranges from ___-____
.5:1 to 2:1
55
a CT pitch of .5:1 means what?
how about CT pitch of 2:1 -
.5:1 CT pitch = overlap and increased patient dose
2:1 CT pitch = extends the image & less patient dose
56
a __lower/higher___ pitch will increase scan speed
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
57
CT pitch and CT scan speed become very important for what type of patients?
breath hold patients
58
what are the 2 types of CT Scanning Data Types?
raw data and image data
59
describe the difference between raw data and image data -
raw data = what is acquired from scan
image data = what we can see and use for planning system
60
what type of data is acquired by system during scan?
raw data
-- ie. scan data
61
raw data/scan data is sent where? to be turned into an image
sent to computer where it is turned into an image
62
____ data includes measurements obtained by detector array
raw data
63
____ data is used to create a variety of images
raw data
64
____ data = the processed raw data that is turned into an image
image data
65
for image data, the computer assigns ____ value to each pixel
HU (Hounsfield Unit)
66
for image data, the computer assigns an HU value to each ____
pixel
67
pixels represent what?
patient tissue
68
SFOV =
Scan Field Of View
69
______ determines the area within the CT gantry that raw data will be acquired
SFOV
Scan Field Of View
70
CT scan data is acquired in a ______ around the isocenter
circle
71
Scan Field Of View can also be called what?
calibration field of view
72
ex. if a 25 cm SFOV is selected, what is the diameter of the circle scan data/circle imaged going to be?
25 cm
73
if a patient is larger, or we want more anatomy what may be do to SFOV?
extend the SFOV
74
how many HU are there?
2000
75
what is HU of air, water, bone
-1000 = air
0 = water
1000 = bone
76
what would have an HU of 2000?
metal
77
what is considered baseline HU?
water at 0
78
monitors can only display how many shades of gray?
human eyes can only detect how many shades of gray?
monitor can display 256 shades of gray
and our eyes can only detect 40 shades of gray
79
describe difference between Window Width (WW) and Window Level (WL) -
WW = range of shades of gray; determines # of HU represented on an image
WL = median; window center; selects center CT value of WW
80
Window Width or Window Level affect brightness the most
WL (window level)
81
Window Width or Window Level affect contrast the most
Window Width (WW)
82
Window Width or Window Level increase/decrease the shades of gray of an image
WW (Window Width)
83
increasing or widening Window _____means more numbers/shades of gray are available
Window Width
84
__more/less__ shades of gray will decrease our image contrast
more gray !
-- more shades of gray between stark black and stark white DECREASE contrast !
85
the following are other names for what term?
--> scout, surview, topogram, scanogram, preview, pilot
localizer scans
86
most CT scans begin w/ one or more ___ images
localizer
--scouts
87
scout images/localizer images are used for what?
to select the region of interest to be scanned (ie. SFOV)!
88
localizer scans/scouts are NOT axial scans!! they are what?
AP or lateral
89
region of interest to be scanned is also known as the _____
SFOV
90
localizer scans/scouts ensure anatomy is in ______ of imaging system
range
91
not having the patient centered on CT can lead to what?
artifacts and clipping
92
___________ estimates values between known values
interpolation algorithms
93
what makes RECONSTRUCTION possible?
interpolation algorithms
94
axial scans are reconstructed to _____ and ___ views
sagittal and coronal views!
95
without interpolation, what would happen to the reconstructed coronal and sagittal views?
they would be blurry!
96
label the planes -
-coronal
-sagittal
-transverse
blue = transverse
yellow = coronal
pink = sagittal
97
which corresponds to Window Width, which for Window Level
A = Window Width
B = Window Level
98
which corresponds to a .5:1 pitch?
which is 2:1 pitch example?
A = .5:1
B = 2:1
99
which corresponds to Gen 3 CT and which is a Gen 4 CT?
A = gen 3
B = gen 4
100
lower the HU value __darker/lighter___ the image
darker
101
higher the HU value __darker/lighter__ the image
lighter/whiter
102
T/F
localizer scans/scouts are NOT cross sectional scans
true
103
localizer scans/scouts are acquired when the tube is ___stationary/not stationary___
stationary !!!
104
the _____ image is used to select region of interest to be scanned/SFOV
scout
105
what estimates the value between known values and makes reconstruction possible?
Interpolation Algorithms
106
axial scans are reconstructed to ________ and __________ views?
coronal and sagittal views
107
CT images are a display of many small pixels with different shades of gray depending on the _______ rate
attenuation rate (ie. HU)
108
define "matrix"
the layout of cells (pixels) in rows and columns
109
define "pixel"
picture elements; pixels are each cell within a matrix; 2D representation
110
define "voxel"
volume element; 3D representation of tissue
111
a voxel is a _____ representation of tissue, whereas a pixel is a _____ representation
voxel = 3D
pixel = 2D
112
(pixel) x (__________) = VOXEL
pixel x slice thickness = voxel
113
bigger matrix sizes have more pixels, this leads to a ___better/worse___ image
better
114
what is the matrix size of CT scanner?
512 x 512 pixels
115
what measures the relative linear attenuation coefficient of tissue?
pixels
116
Hounsfield Units (HU) are also called what?
CT numbers
117
_____ represent tissue density
HU - Hounsfield Units (also can be called CT numbers)
118
what is the HU/CT # of water?
0
119
what is the HU/CT # of air?
-1000
120
what is the HU/CT # of bone?
1000
121
what is the HU/CT # of muscle?
50
122
what is the HU/CT # of blood?
ranges from 30-45
123
what is the HU/CT # of CSF?
15
124
what is the HU/CT # of fat?
ranges from -50 to -100
125
what is the HU/CT # of lung?
ranges from -400 to -600
126
if the HU/CT # is greater than 1000, what is the likely material/tissue?
metal
127
what are differences between CT simulation machines and regular CT machines? *key word = simulation
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
where are the external lasers in a CT sim room?
mounted on side walls/sides and ceiling/above
129
external lasers are how far apart from interal lasers?
500mm or 50 cm
130
are external lasers moveable? YES or NO
---if yes, then in what directions?
YES!
our external lasers move in the sag (x) (ceiling) (lt/rt) and vert (y) (lateral walls) (ant/post)
131
concept check: do the internal lasers go anywhere for CT sim?
no - they are just not used. they stay in CT bore since they are fixed position lasers!
132
is there sup/inf external lasers for CT sim? Why or Why not
no sup/inf laser usage for CT sim... we just move the table
133
what is the point of external lasers for CT sim?
the point of ext lasers for sim is to be able to mark the patient/isocenter outside of the CT bore
134
the higher contrast and higher resolution that we see on our DRRs is achieved how?
with smaller slice thicknesses and smaller spacing
...and adjusting mA - quantity of slices
135
slice thickness is adjusted where?
in the gantry of the CT using collimation
136
thinner slices have ___higher/lower___ image quality? and why
HIGHER quality due to reduced scatter
SBRT/SRS uses this technique
137
thinner CT slices are achieved how?
through more collimation that narrows the xray beam
138
one CT slice delivers about how much dose to patient?
1-6 Gy to skin surface
139
a tighter pitch leads to what?
increased patient dose!
recall: .5:1 ratio = overlap
140
what should CT spacing typically be?
< 5 mm
141
what happens when there is MORE space between each CT slice?
there is less info obtained, so, the scan then has to interpolate more to fill in the gaps
142
DRR is calculated from the _______
CT scan
143
what does DRR stand for?
Digitally Reconstructed Radiograph
144
DRRs are 2D or 3D representation of patient?
2D
145
on trt machine, we know we are looking at a DRR when we see what?
scan with inclusion of MLCs or blocks
146
DRRs are 2D images that show _______
treatment ports
147
we use DRRs to match ____ images
port images
148
kVp = _________
BEAM QUALITY
149
mA = _________
BEAM QUANTITY
150
as mA increases, patient dose ____decreases/increases_____
increases
151
NEMA stands for what?
*hint - it is an Association
National Electrical Manufacturers Association
152
ACR stands for what?
American College of Radiology
153
a virtual simulation is performed when?
after CT sim is complete
154
during a _____ simulation is when outlining of external contours, contours the target volumes, and OARs takes place
virtual
155
T/F: virtual simulation displays ports/beams
true
156
during a _____ simulation is when review of the plan and isodose distribution takes place
virtual
157
RV stood for what (this was on a class exam)
Record & Verify system
158
what does PACS stand for?
Picture Archiving and Communication System
159
what does DICOM stand for?
Digital Imaging and Communication in Medicine
160
the following is describing PACS or DICOM -
-allows for acquisition, interpolation, and storage of digital images
PACS
161
the following is describing PACS or DICOM -
-creates standards for transferring images and radiographic information
-standards are created for sharing images
DICOM
162
the standards for DICOM are produced by a joint committee of who?
NEMA and ACR
163
what are the 4 main principles of PACS?
1. image acquisition
2. display system
3. network
4. storage system
164
label the CT scan -
--green
--purple
--orange
--green = voxel
--purple = pixel
--orange = matrix
165
Slice thickness can affect _______
quality
166
smaller slices = _________ quality
higher
167
increase kvp by ___% = doubles the mas
15%
168
increasing mas, ___increases/decreases___ patient dose ... and increasing kvp __does/does not____ increase patient dose
increase in mas - increases patient dose... and increasing kvp does not increases patient dose
