Exam 4 Flashcards
(134 cards)
1
Q
What does filtration affect?
A
quantity & quality of the x-ray beam
2
Q
When filtering out low energy x-ray photons, the quantity of the beam is ___ & the quality is ____.
A
-quantity- reduced
quality- increased
3
Q
What are the 2 types of filtration (total filtration)?
A
-inherent filtration
-added filtration
4
Q
What does inherent filtration consists of?
A
glass envelope with insulating oil & exit window
5
Q
Added filtration-
A
added after bec total filtration of the X-ray tube must be operating above 70 kVp, at least 2.5 mm of aluminum or its equivelent
6
Q
Compensating filters used to-
A
balance exposure in the image when part thickness varies greatly across the image
7
Q
Types of compensating filters (3)-
A
wedge, trough, & boomerang filter
8
Q
How can compensating filters affect receptor exposure?
A
the part has to be greater than 1cm thick
9
Q
Half-Value Layer can measure-
A
quantity of x-ray beam
10
Q
Half-Value Layer (HVL)
A
thickness of absorbing material necessary to reduce beam intensity by 1/2
11
Q
What does the typical beam have an HVL of?
A
3-5 mm of aluminum
12
Q
Filtration decreases-
A
Receptor exposure & contrast
13
Q
purpose of beam restriction-
A
limit size of exposure area & dose to pt.
14
Q
When limiting the size of the exposure area, what happens to contrast?
A
contrast increases
15
Q
Beam Limiting devices (5)-
A
-manual collimation
-automatic collimation (PBL)
-cylinder/cone- circle on image
-aperature diaphragm- square
-secondary aperture- for off focus radiation
16
Q
off focus radiation-
A
x-rays created when electrons strike anywhere other than focal spot
17
Q
Why were PBL’s created?
A
bec techs weren’t collimating during exams
18
Q
What is the general rule for PBL’s?
A
1/2” beyond the part
19
Q
larger field size/exposure area have more-
A
interactions with matter, therefore more scatter
20
Q
scatter primarily affects-
A
receptor exposure & contrast
21
Q
maintain receptor exposure when changing to a smaller field size-
A
-14x17 - 10x12
-only change mAs- increases by 35%-50%
22
Q
collimation decreases-
A
receptor exposure, scatter
23
Q
As contrast increases, what happens to scatter?
A
scatter decreases
24
Q
collimation increases-
A
contrast
25
Gustof Bucky-
invented radiographic grid in 1913
26
purpose of a grid-
absorb scatter produced in pt. before it reaches IR
27
What is inside a grid?
alternating led strips separated by a radiolucent interspace
28
led absorbs-
scatter in the interspace as x-rays pass through
29
how are led strips placed?
vertically to the x-ray beam
30
What kind of grids are used today?
moving grids & stationary grids
31
purpose of moving grids-
grids that move to get rid of line
32
2 types of movements of moving grids-
-reciprocating
-oscillating
33
reciprocating moving grids-
moves back & forth
34
oscillating moving grids-
moves in a circular motion in only 1 direction
35
Why aren't grids used for every exam?
-small parts produce little/no scatter
-thicker parts have more matter & produce more scatter
36
technical factors affect scatter production bec-
bec the direction it travels (higher kVp more travels to IR
37
use grids when-
-part thickness is greater than 10 cm
-kVp is greater than 60
38
What happens to contrast if scatter never reaches the IR?
contrast increases bec scatter decreases with the use of a grid
39
what is the formula used when using a grid? (CIF)
measured contrast with a grid/measured contrast without a grid
40
What does the contrast improvement formula (CIF) measure-
difference in contrast with & without a grid
41
grid ratio-
major factor in determining efficiency of a grid
42
Grid ratio formula-
grid ratio = H(Height)/D (Distance)
43
what are the common grid ratios (6)?
-5:1
-6:1
-8:1
-10:1
-12:1
-16:1
44
higher grid ratio-
more effective in absorbing scatter (16:1 is most efficient)
45
16:1 grid absorbs ___% of scatter produced by pt
97%
46
5:1 grid absorbs ___% of scatter, even though it is the least efficient.
85%
47
Why don't you always use a 16:1 grid?
it has the least amount of margin of error
48
types of errors made with a grid-
-centering has to be 100% perfect
-perpendicular (no angle)
-on hard flat surface
49
Grid frequency-
-# of led strips per inch in a grid
-anywhere from 60-100 led strips per inch
-not something we can control
50
What is the grid conversion factor for a No Grid ratio?
1
51
What is the grid conversion factor for a 5:1 grid?
2
52
What is the grid conversion factor for a 6:1 grid?
3
53
What is the grid conversion factor for a 8:1 grid?
4
54
What is the grid conversion factor for a 10:1 grid?
5
55
What is the grid conversion factor for a 12:1 grid?
5
56
What is the grid conversion factor for a 16:1 grid?
6
57
How do you maintain intensity when using a grid conversion?
change mAs by correct Bucky factor
58
How do you compensate receptor exposure?
increase mAs
59
Bucky Factor
ratio of exposure (mAs) required with a grid to exposure without a grid
60
When is there going to be a higher grid conversion factor?
when there's a higher grid ratio & higher scatter
61
2 grid patterns-
linear or non-linear
62
linear pattern grid-
has led strips that all go in the same direction
63
non-linear grid pattern-
has led strips that go at a right angle to each other
64
What is another name for a non-linear grid pattern?
-crossed grid
-cross hatch grid
65
What is a cross hatch grid more efficient at?
absorbing more scatter
66
what is the only problem when using a cross hatch grid?
everything has to be lined up perfectly, if not you'll get grid cut off in the image
67
Grid Cut Off
when the grid absorbs the useful x-ray beam
68
linear grids have more ______.
margin of error
69
2 types of grid focus-
parallel & focused
70
parallel grid-
-all straight up & down
-least likely to get grid cut off
71
focused grid-
has canted (angled/tilted) led strips
72
canted led strips-
parallel to divergence of x-ray beam
73
grid radius-
distance from the grid at which lines draw from canted led strips would converge to a focal point
74
When will you get grid cut off in an image?
anytime you angle the tube against the grid lines
75
What will cause grid cut off? (3 things)
-tilting the grid
-X-ray tube pitch
-off centering
76
When using a grid, what decreases?
receptor exposure
77
When using a grid, what increases?
contrast
78
Air gap technique-
reduced amount of scatter on IR without a grid
79
What is the minimum OID that should be used in the air gap technique?
4"-6" (results are similar to using 8:1 grid, don't use OID if possible)
80
positive side of x-ray tube-
anode (left) side
81
negative side of x-ray tube-
cathode (right) side
82
Anode-Heel Effect-
variation in x-ray intensity along longitudinal axis of x-ray tube
83
Intensity is the same as-
quantity
84
intensity isn't going to change ____.
penetrability of x-ray beam
85
intensity of x-ray beam ___ toward anode side of exposure area.
decreases
86
intensity of x-ray beam ___ toward cathode side of exposure area.
increases
87
How much intensity is there where the exposure area or central ray enters?
100% intensity
88
makes anode-heel effect more noticeable- (3)
-combination of short SID & large field size
-anode bevel with more acute/steeper angles
-use of a large focal spot size
89
ex. of small field size-
40" SID
90
ex. of large field size-
72" SID
91
exams that utilize anode-heel effect- (40" SID with collimation open all the way to 14x17) (3)
AP Abdomen, T-Spine, & Femur
92
cathode side placed over ___ anatomy-
thicker anatomy
93
anode side placed over ____ anatomy-
less dense anatomy
94
2 types of shape distortion-
elongation & foreshortening
95
elongation-
object in an image longer than what it actually is
96
foreshortening-
object in an image shorter than what it actually is
97
shape distortion attributes to- (3)
-beam/part alignment
-beam/IR alignment
-part/IR alignment
98
Why is the x-ray tube angled for some exams?
so beam can be perpendicular to the part
99
4 things affecting shape distortion-
-shape of an object
-centering of CR in respect to the object
-angle btwn CR & long axis of the object
-angle btwn long axis of the object & IR
100
CR should be ___ & part should be _____ to IR.
-perpendicular
-parallel
101
can get shape distortion from- (4)
-off center (CR not centered to IR or part)
-CR not perpendicular to IR or part
-angling the part
-part not parallel to IR
102
when you angle the x-ray tube you're _____ & _____.
increasing SID & changing distance
103
SID increases as the tube is angled, to compensate-
when angling more than 15* divide the tube angle by 5, then subtract that # from SID
104
purpose of AEC-
determine when enough exposure has reached IR
105
angling x-ray tube DOES NOT AFFECT-
receptor exposure
106
different body habitus-
hyposthenic, hypersthenic, sthenic, & asthenic
107
size of patient affects tech factors-
affects absorption of x-ray beam
108
calipers-
measurement device to measure thickness of pt. where CR enters to where it exits
109
additive disease-
adds something to body that shouldn't be there
110
destructive disease-
takes away from body that shouldn't be there
111
additive disease could add-
fluid, bone, or prosthetic devices
112
How does additive disease affect receptor exposure?
absorbs more of x-ray beam & causes RE to decrease
113
if there's an increase in mineral content (bone formation) in additive diseases, how much should kVp be increased by?
8%
114
if there's an increase in fluid in additive diseases, how much should mAs be increased by?
35%-50%
115
pneumonia-
increased fluids in lungs
116
paget's disease-
increased bone formation
117
destructive disease could add/take away-
-decrease in fluid/mineral content
-or increase in air/fat content
118
osteoperosis-
decrease in mineral content in bones
119
emphysema-
more air in lungs than supposed to be, less penetration is required
120
if normal tech. factors used in destructive disease-
factors would increase receptor exposure bec there is less there to absorb x-ray beam
121
How much should kVp & mAs be decreased if destructive diseases are present?
-kVp 8%
-mAs- 35%-50%
122
tech. factors for soft tissue technique should be-
decreased
123
general rule for soft tissue techniques-
decrease kVp by 15% & mAs is unchanged
124
typical cast usually requires _____ of exposure-
doubling of exposure
125
when extra thick/wet cast increase tech. factors by-
factor of 3
126
inflatable cast/air splints, tech factors-
remain unchanged
127
contrast media
helps visualize internal structures of body that normally can't be seen on a radiograph
128
is called contrast media bec-
it creates the difference in contrast
129
positive contrast-
iodine/barium
130
negative contrast-
air
131
optimal kVp to penetrate through iodinated contrast media-
76-80
132
optimal kVp for barium only studies-
116-120
133
optimal kVp for barium & air contrast exams
90-94
134
patient factors affect-
receptor exposure, contrast, spatial resolution, & distortion
