Image Aquistion Flashcards
(124 cards)
1
Q
matrix size and pixel size relationship
A
inversely related
2
Q
FOV and pixel size relationship
A
direct
3
Q
pixel size and resolution relationship
A
inversely related
4
Q
small pixel size and resolution
A
small pixel size has a high resolution
5
Q
what pixel size has a 512X512 matrix with a 20 cm FOV
A
.40 mm/pixel
change 20 to mm then take 200/512 =.39
6
Q
how do you find the pixel size
units?
A
take the FOV (mm) and divide it by the matrix (FOV/matrix)
units: mm/pixels
7
Q
pixel depth
A
dynamic range
how many shades of gray
8
Q
bit size equation
so a 6-bit =
A
2^n
6 bit = 2^6 = 64
9
Q
spatial resolution is measured in?
A
line pairs/mm
lp/mm
10
Q
matrix is made up of
A
columns and rows
11
Q
what does filtration do to the intensity of the beam?
A
decreases it bc there are less photons
12
Q
moire effect definition:
when is the moire effect seen
A
having wavy lines
seen when using stationary grids
13
Q
grids are composed of
A
lead
aluminum
plastic fibers
14
Q
kVp and contrast relationship
A
inversely related
15
Q
what pulse does CT use?
A
short pulse
16
Q
mAs and density
A
higher mAs has higher density
17
Q
the component of a CR IP that records the radiologic image
A
PSP
18
Q
PSP’s store what kind of image
how long does it store it for
A
latent
8 hours
19
Q
DXA is used to see
A
bone mineral density
20
Q
radiation dose in DXA
A
low
21
Q
the luminescent light emitted by the PSP is transformed into the image seen on the CRT by the
A
ADC
22
Q
insufficient back up time would have what effect on the image
A
underexposed
23
Q
focal spot size is measured by what tests
A
pinhole camera
slit camera
star pattern type
24
Q
kVp and exposure rate relationship
A
direct bc an increase in kV (photon energy) will result in a greater number (exposure rate) of scattered photons
25
as field size decreases, scatter ______, and image quality _______.
scatter decreases
| image quality increases
26
what is very important when using AEC
accurate positioning
27
the negative aspect of CR
has a limited spatial resolution
28
best spatial resolution
film screen
29
windowing refers to
changing the image brightness and/or contrast
30
changes in window width
changes number of grays, which is contrast resolution
31
changes in window level
changes the image brightness
32
FOV describes how much ____ is included in the ____
pt
| matrix
33
foreshortening can be caused by
angling the part
34
elongation can be caused by
angling the tube
35
size distortion is aka
magnification
36
each cm increase in pt thickness requires what adjustment to kVp?
increase 2 kV to the exposure
37
what is the proper way to store film screen inventory (if you were stocking) bc
upright bc if they are stacked on top of each other there is a loss of contrast
38
what contributes to film fog?
the age of the film
excessive exposure to safelight
processor chemistry
39
outdated film will have what kind of contrast
loss of contrast, which causes fog
40
photon energy and wavelength relationship
inverse
as kV is increased, more high energy photons are produced, the overall energy of the beam is increased. so the wavelength is decreased
41
an increase in mA does what to the number of photons produced at the target
increases
42
for an abdomen xray, which needs more exposure, supine or erect? why?
erect because everything in the stomach sits lower when they are standing, whereas when they lay everything spreads out and thickness of the stomach decreases
43
solid state detector plates (in DR) are made of
barium fluorohalide
44
height of the lead strips to the width of the interspaces describes
grid ratio
45
what type of grid ratio allows for more centering latitude?
low grid ratio
| high grid ratios need to be accurate
46
TECHNICAL FACTORS
| INCREASE OR DECREASE
TECHNICAL FACTORS
| INCREASE OR DECREASE
47
Ascites
fluid in the abdomen
increase
48
Osteoporosis
weakening of bone
decrease
49
Osteomalacia
softening of bones
decrease
50
Rheumatoid arthritis
hardening of the joints
increase
51
paget disease
increase
52
pneumoperitoneum
air in the abdomen
decrease
53
pneumonia
fluid filled air sacs of the lungs
increase
54
atelectasis
collapsed lung
increase
55
emphysema
breaks down air sacs in the lungs
decrease
56
congestive heart failure
increase
57
edematous tissue
fluid in the tissues
increase
58
degenerative arthritis
decrease
58
atrophic and necrotic conditions
shrinkage or death
decrease
59
BREAK
BREAK
60
low ratio grids and high ratio grids allow for how much scatter to reach the IR
low ratio grids allow for a great percentage of scatter to reach the IR
high ratio grids allow for a small percentage of scatter to reach the IR bc it will clean up more scatter
61
mAs and scatter
no relation
62
grids and contrast
grids improve contrast
63
exposure rate is determined by
kV
mA (most)
distance
64
high kV and scatter
high kV increases scatter
65
thick/dense structures and scatter
increases scatter
66
the degree of difference between adjacent denstities
radiographic contrast
67
mA and contrast
no relation
68
what is the equation for grid ratio
the height of the strips / the width between them
69
a 5 in object to be radiographed at 44 in. SID lies 6 in. from the IR. what will be the image width
Image size SID X 44in
__________ = _______ _____ = ______ = 5.78
object size SOD (SOD=SID-OID) 5in 38in
70
SOD =
SID-OID
71
in comparison with 60 kV, 80 kV will do what to scatter and exposure latitude
produce more scatter
and
allow for greater exposure latitude (margin of error)
72
two-dimensional, pixel element, thats measured in XY direction
pixel
73
how much of the patient is included in the matrix describes?
FOV
74
mosiaicked
pixelly
75
misalignment of the tube-part-IR relationship results in
shape distortion (elongation/foreshortening)
76
focal spot blur is caused by..
the use of a large focal spot
77
size distortion
magnification
78
what can cause grid cut-off when using a focused reciprocating grid?
inadequate SID
79
central ray angulation in the direction of the lead strips causes:
central ray angulation against the direction of the lead strips causes:
in the direction: causes nothing
against the direction: causes grid cut off
80
phantom images are a result of
incomplete erasure of the previous image on the PSP
81
what increases the anode heel effect
short SID with large IR
10 degree or less angle
82
low ratio grids and exposure latitude
low ration grids offer more exposure latitude than high grid ratios
83
Z direction in a matrix
voxel
| volume element
84
to magnify an object 2X
the OID must be half the distance of the SID
85
what is the main difference between direct capture and indirect capture DR
direct capture has no scintillator
| indirect capture has a scintillator
86
the direction electrons travel in the xray tube is
cathode to anode
87
Charges
Anode:
Cathode:
Which way do these charges travel in an xray tube
Anode: positive
Cathode: Negative
Cathode to Anode so negative to positive
88
when tissue densities are very different (like a chest xray) what can be done to "even out" the densities on the image
increase kV to use a longer scale of contrast (which results in more grays)
89
for the same FOV, spatial resolution will be improved using..
a larger matrix
or
smaller (NOT FEWER) pixels
matrix and pixel size are inversely related
90
FOV and resolution relationship
inverse relationship
| Decreasing the FOV, decreases the pixel size, which improves resolution
91
which of the following are methods of limiting the production of scattered radiation and why/why not?
1. using moderate grid ratios
2. using prone position for abdominal xrays
3. restricting the field size
2. using prone position for abdominal xrays: because it will compress the stomach, causing less scatter
3. restricting the field size: most effective means of reducing scatter
not 1. using grids: because grids cleanup scatter and have nothing to do with the PRODUCTION of scatter
92
the absorption of useful radiation by a grid is called?
grid cut off
93
radiographic density is found by what factors?
mAs and distance
| high mAs with short distance produces the greatest density
94
```
which factor will produce the shortest scale of contrast
70 kV, 8:1 grid
70 kV, 6:1 grid
95 kV, 12: grid
95 kV, 8:1 grid
```
70 kV, 8:1 grid
want low kVp, bc low kV, high contrast, short scale
and
higher grid ratio cleans up scatter reaching the IR, therefor fewer grays
95
long scale contrast has___ kV and what type of grid ratio?
high kV, low contrast, long scale
| lower grid ratio bc more scatter will reach the IR (producing more grays)
96
kV and exposure latitude relationship
direct
97
actual focal spot and effective focal spot size
actual focal spot is larger than the effective/projected focal spot
98
focal spot blur is greatest at what part of the xray beam
toward the cathode end of the x-ray beam
99
BREAK
BREAK
100
mAs and pt dose relationship
direct relationship
101
IPs can be made from?
carbon fiber
and
magnesium
102
if the grid failed to move throughout the exposure, how would the image look?
there would be grid lines throughout the image
103
if the central ray was off center, how would the image look?
it would have a uniform loss of density
| the whole image would have a loss of density/ increased brightness
104
if the SID is above or below the recommended focusing distance, what will the image look like?
there would be an increased brightness/loss of density at its lateral edges
105
what can be done to reduce the exposure time?
increase mA
or
increase kV
106
energy and wavelength
inverse
| high energy, short wavelength
107
film processing order
develop, fix, wash, dry
108
SID and exposure factors relationship
direct
| increased SID causes for increased exposure factors (kV or mA)
109
SID and density relationship
inverse
| short SID, more density
110
Grid cut off is due to
Improper tube and grid alignment
111
Grid cut off and contrast relationship
Grid cut off increases contrast
112
the function of the developer in the film processor
change the EXPOSED silver bromide crystals to black metallic silver
113
quantum noise is due to what factor
| whats its appearance
too low mAs
or too much kV
grainy
114
short SID results in? under/over exposure
overexposure
115
does the HVL affect tissue density?
no
116
magnification factor (MF)=
image size/ object size
117
DR patient dose
low
118
major advantage to CR
has best/widest dynamic range/latitude
119
screen speed and contrast
faster the screens the higher the contrast
| direct relationship
120
health informatics aka
| ex
health care information technology
PACS
HIS
RIS
121
the xray image seen on the computer monitor is?
analog image
122
.3mm or smaller focal spot size is for?
magnification
123
is the anode heel effect good for....
lateral T-spine
AP femur
RAO sternum
lateral T-spine
| AP femur
