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Radt. 3000 > Exam 4 > Flashcards

Exam 4 Flashcards

1
Q

What does filtration affect?

A

quantity & quality of the x-ray beam

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2
Q

When filtering out low energy x-ray photons, the quantity of the beam is ___ & the quality is ____.

A

-quantity- reduced
quality- increased

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3
Q

What are the 2 types of filtration (total filtration)?

A

-inherent filtration
-added filtration

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4
Q

What does inherent filtration consists of?

A

glass envelope with insulating oil & exit window

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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

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6
Q

Compensating filters used to-

A

balance exposure in the image when part thickness varies greatly across the image

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7
Q

Types of compensating filters (3)-

A

wedge, trough, & boomerang filter

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8
Q

How can compensating filters affect receptor exposure?

A

the part has to be greater than 1cm thick

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9
Q

Half-Value Layer can measure-

A

quantity of x-ray beam

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10
Q

Half-Value Layer (HVL)

A

thickness of absorbing material necessary to reduce beam intensity by 1/2

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11
Q

What does the typical beam have an HVL of?

A

3-5 mm of aluminum

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12
Q

Filtration decreases-

A

Receptor exposure & contrast

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13
Q

purpose of beam restriction-

A

limit size of exposure area & dose to pt.

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14
Q

When limiting the size of the exposure area, what happens to contrast?

A

contrast increases

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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

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16
Q

off focus radiation-

A

x-rays created when electrons strike anywhere other than focal spot

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17
Q

Why were PBL’s created?

A

bec techs weren’t collimating during exams

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18
Q

What is the general rule for PBL’s?

A

1/2” beyond the part

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19
Q

larger field size/exposure area have more-

A

interactions with matter, therefore more scatter

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20
Q

scatter primarily affects-

A

receptor exposure & contrast

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21
Q

maintain receptor exposure when changing to a smaller field size-

A

-14x17 - 10x12
-only change mAs- increases by 35%-50%

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22
Q

collimation decreases-

A

receptor exposure, scatter

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23
Q

As contrast increases, what happens to scatter?

A

scatter decreases

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24
Q

collimation increases-

A

contrast

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25
Q

Gustof Bucky-

A

invented radiographic grid in 1913

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26
Q

purpose of a grid-

A

absorb scatter produced in pt. before it reaches IR

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27
Q

What is inside a grid?

A

alternating led strips separated by a radiolucent interspace

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28
Q

led absorbs-

A

scatter in the interspace as x-rays pass through

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29
Q

how are led strips placed?

A

vertically to the x-ray beam

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30
Q

What kind of grids are used today?

A

moving grids & stationary grids

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31
Q

purpose of moving grids-

A

grids that move to get rid of line

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32
Q

2 types of movements of moving grids-

A

-reciprocating
-oscillating

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33
Q

reciprocating moving grids-

A

moves back & forth

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34
Q

oscillating moving grids-

A

moves in a circular motion in only 1 direction

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35
Q

Why aren’t grids used for every exam?

A

-small parts produce little/no scatter
-thicker parts have more matter & produce more scatter

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36
Q

technical factors affect scatter production bec-

A

bec the direction it travels (higher kVp more travels to IR

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37
Q

use grids when-

A

-part thickness is greater than 10 cm
-kVp is greater than 60

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38
Q

What happens to contrast if scatter never reaches the IR?

A

contrast increases bec scatter decreases with the use of a grid

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39
Q

what is the formula used when using a grid? (CIF)

A

measured contrast with a grid/measured contrast without a grid

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40
Q

What does the contrast improvement formula (CIF) measure-

A

difference in contrast with & without a grid

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41
Q

grid ratio-

A

major factor in determining efficiency of a grid

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42
Q

Grid ratio formula-

A

grid ratio = H(Height)/D (Distance)

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43
Q

what are the common grid ratios (6)?

A

-5:1
-6:1
-8:1
-10:1
-12:1
-16:1

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44
Q

higher grid ratio-

A

more effective in absorbing scatter (16:1 is most efficient)

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45
Q

16:1 grid absorbs ___% of scatter produced by pt

A

97%

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46
Q

5:1 grid absorbs ___% of scatter, even though it is the least efficient.

A

85%

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47
Q

Why don’t you always use a 16:1 grid?

A

it has the least amount of margin of error

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48
Q

types of errors made with a grid-

A

-centering has to be 100% perfect
-perpendicular (no angle)
-on hard flat surface

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49
Q

Grid frequency-

A

-# of led strips per inch in a grid
-anywhere from 60-100 led strips per inch
-not something we can control

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50
Q

What is the grid conversion factor for a No Grid ratio?

A

1

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51
Q

What is the grid conversion factor for a 5:1 grid?

A

2

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52
Q

What is the grid conversion factor for a 6:1 grid?

A

3

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53
Q

What is the grid conversion factor for a 8:1 grid?

A

4

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54
Q

What is the grid conversion factor for a 10:1 grid?

A

5

55
Q

What is the grid conversion factor for a 12:1 grid?

A

5

56
Q

What is the grid conversion factor for a 16:1 grid?

A

6

57
Q

How do you maintain intensity when using a grid conversion?

A

change mAs by correct Bucky factor

58
Q

How do you compensate receptor exposure?

A

increase mAs

59
Q

Bucky Factor

A

ratio of exposure (mAs) required with a grid to exposure without a grid

60
Q

When is there going to be a higher grid conversion factor?

A

when there’s a higher grid ratio & higher scatter

61
Q

2 grid patterns-

A

linear or non-linear

62
Q

linear pattern grid-

A

has led strips that all go in the same direction

63
Q

non-linear grid pattern-

A

has led strips that go at a right angle to each other

64
Q

What is another name for a non-linear grid pattern?

A

-crossed grid
-cross hatch grid

65
Q

What is a cross hatch grid more efficient at?

A

absorbing more scatter

66
Q

what is the only problem when using a cross hatch grid?

A

everything has to be lined up perfectly, if not you’ll get grid cut off in the image

67
Q

Grid Cut Off

A

when the grid absorbs the useful x-ray beam

68
Q

linear grids have more ______.

A

margin of error

69
Q

2 types of grid focus-

A

parallel & focused

70
Q

parallel grid-

A

-all straight up & down
-least likely to get grid cut off

71
Q

focused grid-

A

has canted (angled/tilted) led strips

72
Q

canted led strips-

A

parallel to divergence of x-ray beam

73
Q

grid radius-

A

distance from the grid at which lines draw from canted led strips would converge to a focal point

74
Q

When will you get grid cut off in an image?

A

anytime you angle the tube against the grid lines

75
Q

What will cause grid cut off? (3 things)

A

-tilting the grid
-X-ray tube pitch
-off centering

76
Q

When using a grid, what decreases?

A

receptor exposure

77
Q

When using a grid, what increases?

A

contrast

78
Q

Air gap technique-

A

reduced amount of scatter on IR without a grid

79
Q

What is the minimum OID that should be used in the air gap technique?

A

4”-6” (results are similar to using 8:1 grid, don’t use OID if possible)

80
Q

positive side of x-ray tube-

A

anode (left) side

81
Q

negative side of x-ray tube-

A

cathode (right) side

82
Q

Anode-Heel Effect-

A

variation in x-ray intensity along longitudinal axis of x-ray tube

83
Q

Intensity is the same as-

A

quantity

84
Q

intensity isn’t going to change ____.

A

penetrability of x-ray beam

85
Q

intensity of x-ray beam ___ toward anode side of exposure area.

A

decreases

86
Q

intensity of x-ray beam ___ toward cathode side of exposure area.

A

increases

87
Q

How much intensity is there where the exposure area or central ray enters?

A

100% intensity

88
Q

makes anode-heel effect more noticeable- (3)

A

-combination of short SID & large field size
-anode bevel with more acute/steeper angles
-use of a large focal spot size

89
Q

ex. of small field size-

A

40” SID

90
Q

ex. of large field size-

A

72” SID

91
Q

exams that utilize anode-heel effect- (40” SID with collimation open all the way to 14x17) (3)

A

AP Abdomen, T-Spine, & Femur

92
Q

cathode side placed over ___ anatomy-

A

thicker anatomy

93
Q

anode side placed over ____ anatomy-

A

less dense anatomy

94
Q

2 types of shape distortion-

A

elongation & foreshortening

95
Q

elongation-

A

object in an image longer than what it actually is

96
Q

foreshortening-

A

object in an image shorter than what it actually is

97
Q

shape distortion attributes to- (3)

A

-beam/part alignment
-beam/IR alignment
-part/IR alignment

98
Q

Why is the x-ray tube angled for some exams?

A

so beam can be perpendicular to the part

99
Q

4 things affecting shape distortion-

A

-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
Q

CR should be ___ & part should be _____ to IR.

A

-perpendicular
-parallel

101
Q

can get shape distortion from- (4)

A

-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
Q

when you angle the x-ray tube you’re _____ & _____.

A

increasing SID & changing distance

103
Q

SID increases as the tube is angled, to compensate-

A

when angling more than 15* divide the tube angle by 5, then subtract that # from SID

104
Q

purpose of AEC-

A

determine when enough exposure has reached IR

105
Q

angling x-ray tube DOES NOT AFFECT-

A

receptor exposure

106
Q

different body habitus-

A

hyposthenic, hypersthenic, sthenic, & asthenic

107
Q

size of patient affects tech factors-

A

affects absorption of x-ray beam

108
Q

calipers-

A

measurement device to measure thickness of pt. where CR enters to where it exits

109
Q

additive disease-

A

adds something to body that shouldn’t be there

110
Q

destructive disease-

A

takes away from body that shouldn’t be there

111
Q

additive disease could add-

A

fluid, bone, or prosthetic devices

112
Q

How does additive disease affect receptor exposure?

A

absorbs more of x-ray beam & causes RE to decrease

113
Q

if there’s an increase in mineral content (bone formation) in additive diseases, how much should kVp be increased by?

A

8%

114
Q

if there’s an increase in fluid in additive diseases, how much should mAs be increased by?

A

35%-50%

115
Q

pneumonia-

A

increased fluids in lungs

116
Q

paget’s disease-

A

increased bone formation

117
Q

destructive disease could add/take away-

A

-decrease in fluid/mineral content
-or increase in air/fat content

118
Q

osteoperosis-

A

decrease in mineral content in bones

119
Q

emphysema-

A

more air in lungs than supposed to be, less penetration is required

120
Q

if normal tech. factors used in destructive disease-

A

factors would increase receptor exposure bec there is less there to absorb x-ray beam

121
Q

How much should kVp & mAs be decreased if destructive diseases are present?

A

-kVp 8%
-mAs- 35%-50%

122
Q

tech. factors for soft tissue technique should be-

A

decreased

123
Q

general rule for soft tissue techniques-

A

decrease kVp by 15% & mAs is unchanged

124
Q

typical cast usually requires _____ of exposure-

A

doubling of exposure

125
Q

when extra thick/wet cast increase tech. factors by-

A

factor of 3

126
Q

inflatable cast/air splints, tech factors-

A

remain unchanged

127
Q

contrast media

A

helps visualize internal structures of body that normally can’t be seen on a radiograph

128
Q

is called contrast media bec-

A

it creates the difference in contrast

129
Q

positive contrast-

A

iodine/barium

130
Q

negative contrast-

A

air

131
Q

optimal kVp to penetrate through iodinated contrast media-

A

76-80

132
Q

optimal kVp for barium only studies-

A

116-120

133
Q

optimal kVp for barium & air contrast exams

A

90-94

134
Q

patient factors affect-

A

receptor exposure, contrast, spatial resolution, & distortion

Radt. 3000 (6 decks)

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