1
Q
what are the 2 major limitations of conventional radiography
A
- low in contrast
- lots of superimposition
2
Q
a large tomographic angle creates a ___ thickness of cut
A
small thickness
3
Q
a small tomographic angle creates a ___ thickness of cut
A
large thickness of cut
4
Q
what is the difference between conventional tomography, versus CT
A
conventional: axial tomography
CT: trans axial or transverse
5
Q
explain axial tomography
A
parallel to long axis of body
sagittal or coronal images
6
Q
explain trans axial or transverse CT
A
perpendicular to the long axis of the body
7
Q
what determines slice thickness of first gen CT scanners
A
beam width
8
Q
first gen CT scanners aquired what type of images/slices
A
axial slices
9
Q
what was the scanning process of first gen CT scanners
A
the tube and detector scan across the subject
rotate 1 degree
scan again in opp direction
10
Q
how many views did first gen CT scanners collect over 180 degrees
A
180
11
Q
what type of motion did first gen CT scanners use?
A
translate-rotate motion **
12
Q
what was the imaging time for first gen CT scanners
A
5 minutes
13
Q
what was the beam difference in 2nd gen scanners
A
used a fan beam
14
Q
what kind of motion do 2nd gen use
in what increments
A
translate-rotate
5-10 degree increments
15
Q
how many cells make up the 2nd gen detector array
A
5-30 detector cells
16
Q
what are the pros of 2nd gens (2)
A
- faster, so less imaging time
- scan could be potentially performed in a breath hold (20-30 sec)
17
Q
about how fast could 2nd gens scan
A
20-30 seconds
18
Q
what are the cons of 2nd gen (3)
A
heavier tube with vibrating electronics
scan time still too long
unequal attenuation
19
Q
what type of filter must be used with fan beams
A
bow tie filter
20
Q
what type of movement do 3rd gen use
A
rotate-rotate
21
Q
how much does the 3rd gen fan beam cover
A
the entire patient
22
Q
what type of detector is used in 3rd gen
A
curvilinear detractor array
23
Q
what is the 3rd gen imaging time
A
sub-second image time
24
Q
what are the 2 types of 3rd gen collimation
A
pre-pt collimator
pre-detector collimator
25
what is SSCT
single slice per revolution scanners
26
what is the major disadvantage to SSCT scanners
ring artifact
27
how do ring artifacts happen
just one faulty detector can cause it
28
what is CAT
computed axial tomography
29
how does interscan delay happen on CATs
table is moving to next location (when they had single rows)
30
what moves in CAT
CT table/couch moves and remains stationary while the tube rotates within the gantry
31
what gen is this
first
32
what gen is this
second
33
what gen is this
third
34
what gen is this
third
35
what generation are MDCT scanners
third
36
what is MDCT
multi detector computed tomography
37
what was improved with mdct
temporal resolution
38
what is temporal resolution
the ability to capture and resolve images of fast-moving structures
39
what are slip rings
set or parallel, stationary, electrically conductive rings
in contact with conductive brushes or blocks
40
what do slip rings do
supply voltage without the need to respool every 360 degrees
41
what is this
slip rings
42
what are the advantages of slip ring technology (4)
facilitates continuous rotation (no interscan delay)
less motion artifacts
quicker scans
improved temporal reoslution
43
what is spiral/helical scanning
slices begin and end at different points on the same z-axis
44
what type of scanning is this
helical scanning
45
what removes the slant and blur resulting from helical scanning
interpolation
46
what do 4th gen scanners do
rotating tube within a circular detector array
47
what gen scanners is this
fourth
48
what are the 3 major steps of CT image formation
1. data acquisition
2. image reconstruction
3. image display
49
what happens during data acquisition
detectors measure attenuation values
data is converted into binary for input into the computer
50
what does DAS stand for
data acquisition system
51
what is the DAS
the electronics positioned between the detector array and computer
52
what does the DAS do
measures the transmitted beam, encodes into binary, and transmits to the computer
53
where is raw data stored
in the RAM of the computer attached to the CT system
54
the reconstructed image is in what form
numerical form
55
can the reconstructed image be viewed in numerical form?
no!
56
where are the images sent when complete?
into PACS
57
what is the analog signal
the attenuation measurements
58
where does the signal become digital
when translated to the numerical CT image
59
what is CT detector efficiency?
the ability to capture, absorb, and convert photons into electrical signals
60
what 3 types of efficiency must CT detectors possess
capture
absorption
conversion
61
what is capture efficiency
ability to capture photons transmitted from the patient
62
what determines capture efficiency
size of detector area
distance
63
what is absorption efficiency
number of photons absorbed by the detector
64
what does absorption efficiency depend on (4)
atomic number
physical density
size
thickness of detector face
65
what is conversion efficiency
how well the detector converts the incoming x-rays to a digital signal
66
what is the response time or resolving time
recovery time between detecting x-ray events
67
what is afterglow
the persistence of the image after the radiation is turned off
68
what shoulde the CT afterglow values be
<0.01%, 100 milliseconds after termination
69
what is the dynamic range
ratio of largest to smallest signal that can be measured
70
what is the average CT dynamic range
1 million : 1
71
what is total detector efficiency
product of capture efficiency, absorption efficiencym, and conversion efficiency
72
what are solid state scintillation detectors
detector elements are affixed to a circuit board
73
what materials are used for solid state scintillation detector photodiodes
cadmium tungstinate and ceramic
gadolinium oxysulsife with ultrafast ceramic
74
chem formula for cadmium tungstinate
CdWO4
75
chem for gadolinium oxysulfide
Gd2O2S
76
what are the 2 categories of multi-row CT detectors
matrix array detectors
adaptive array detectors
77
what are matrix array detectors
(fixed array detectors)
cells have equal dimensions
78
what are adaptive array detectors
cells have unequal dimensions
79
how big is the CT gantry
70-90 cm
80
R1
gantry
81
R2
gantry aperture
82
what needs to be changed regularly on the gantry
the filters
83
what is the tilting ability of gantry angulation for most CT machines
+/- 30 degrees
84
what is the rough weight limit of the CT table
200-300 kg
85
what is indexing
a way to ensure that the machine knows where it is on the table
86
what determines the image reconstruction time
microprocessors (RAM)
primary memory
87
the x plane goes where
left to right across pt
88
the y plane goes where
anterior to posterior on pt
89
the z plane goes where
head to toe on pt
90
what is the isocentre
the point in the gantry where all 3 axes intersect
91
what is the difference between a pixel and a voxel
voxel is basically a 3D pixel
92
what reconstruction matrix size do current systems have
512 x 512
93
Pixel size = ?
FOV / matrix size
94
what is a scout / scanogram / topogram
low dose x-ray taken prior to CT
used to choose FOV
95
Ni = ?
N0 e ^-mu x
96
what is the formula for CT atenaution
Ni = No e ^-mu x
97
what was the first reconstruction technique
ART
algebraic reconstruction technique
98
what reconstruction technique do most systems use
analytical reconstruction algorithms
99
how do analytical reconstruction algorithms work
filtered back-projection
interpolation
100
how does iterative reconstruction work
start with an assumed value
compare to measured
make corrections until match or acceptable
101
what are the advantages of iterative reconstruction
reduce image noise and artifacts
lower pt dose
102
what is the disadvantage of iterative reconstruction
takes a long time, lots of effort from the computer
103
how does FBP work
filtered back projection
"smears back" the image to reconstruct
104
what is another term for FBP
convolution method
105
how is FBP blur supressed
using mathematical filters
106
what is the (physical) thing that reduces FBP blur
convolution filter
kernel
107
what does the sharpening filter do
reduces blur
accentuates noise
108
what does the smoothing filter do
decreases noise
increases blur
109
what is interpolation
method of estimating the value of an unknown using known values on either side
110
what is pitch
ratio of pt table movement to width of beam
111
if distance traveled by table is equal to beam width, what is the pitch and pitch ratio
1, 1:1
112
what (geometrically) does a pitch of 2:1 indicate
table will move twice the distance of the slice thickness, each rotation of the gantry
113
in SDCT, beam width = ?
slice thickness
114
in MDCT, beam width = ?
slice thickness x n of slices
115
what is the pitch that creates contiguous slices
1
116
what happens to dose when pitch is >1
reduced
117
what happens to pt dose when pitch is <1
increased
118
CT number = ?
mu - muw / muw x1000
119
what is muw
attenuation coefficients of water
**changes based on keV
120
what is the hounsfield n of water
0
121
what is the hounsfield number of fat
-100
122
what is the hounsfield n of soft tissue
+50
123
what is the hounsfield n of air
-1000
124
what is the hounsfield n of bone/metal
+1000
125
why does beam hardening happen
polychromatic beams increase in quality as they penetrate
126
do deeper values have higher or lower mu n? why?
lower as deeper
due to beam hardening
127
beam hardening causes what
cupping artifact
128
how does CT simulation help in radiation therapy
localize and provide info
simulation plans treatment, dose distribution, and treatment isocentre and beams
129
what are the 3 steps of CT simulation
1. pt scanning
2. treatment planning and CT simulation
3, treatment setup
130
what is quantitative CT
most sensitive x-ray tehcnique
for measurement of BMC in osteoporosis
131
what is DECT
dual energy ct
132
what is dual energy ct
uses 2 energies to differentiate similar attenuating materials
133
what 4 methods can be used to perform DECT
- sequential acquisition of 2 separate scans
- rapid tube potential switching
- multilayer detectors
- dual x-ray sources
134
what is the pro of rapid kVp switching
near-simultaneous data acquisition of high and low
135
what are the cons of rapid kVp switching (4)
transitions must be abrupt
requires rapidly modulating mA
difficult to filter
requires very fast electronics and good generator
136
how does a multilayer detectors work
1 (high) tube potential
low E is collected by front detector
high E is collected by back detector
TRT STUDYING
flashcards
Decks in class (66)
# Cards
-
introduction6
-
upper extremities8
-
lower extremities1
-
Surgical OR9
-
Mobile Imaging18
-
Trauma Radiography11
-
Interventional Radiography 1120
-
Interventional Radiography 234
-
Intro to the body78
-
cells and tissues39
-
osseous tissue80
-
articulations93
-
upper extremity86
-
lower extremity163
-
cranium119
-
facial bones COPY77
-
vertebrae and bony thorax COPY158
-
respiratory system109
-
digestive system COPY247
-
heart COPY208
-
urinary system COPY197
-
nervous system & spinal cord157
-
brain part 1100
-
brain 2111
-
cardiovascular vessels 2 COPY141
-
cardiovascular vessels 2104
-
lymphatic system COPY60
-
muscular system COPY161
-
endocrine system COPY74
-
reproductive system COPY50
-
med rad imaging overview13
-
electricity65
-
magnetism33
-
generators25
-
x-ray tube parts 1 & 275
-
beam restriction11
-
beam geometry30
-
electromagnetic radiation21
-
x-ray production15
-
attenuation processes19
-
attenuation applications9
-
mammography15
-
attenuation and coefficients0
-
attenuation, HVL and beam quality0
-
radiation electronics and detection0
-
computed tomography136
-
radioactivity COPY64
-
nuclear medecine COPY109
-
magnetic resonance imaging COPY90
-
ultrasound COPY82
-
infection control56
-
aseptic techniques in medical imaging10
-
pharmaceutical tables0
-
pharmaceutical tables (competency)49
-
pharmacology and medication administration0
-
contrast media and venipuncture65
-
medical emergencies62
-
lines and tubes32
-
oxygen and suction101
-
vital signs120
-
lab & review questions28
-
lines and tubes32
-
midterm pharm75
