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Radt. 3011 > Exam 3 Ch 22- Scatter Production > Flashcards

Exam 3 Ch 22- Scatter Production Flashcards

1
Q

3 main factors that contribute to production of scatter-

A

kVp, field size, & patient thickness

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2
Q

The only x-ray photons that are incident on an IR are-

A

those that didn’t interact with the patient

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3
Q

3 main tools for controlling scatter-

A

beam restriction, grids, & compression (not talked ab a lot)

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4
Q

3 types of x-rays responsible for imaging on a radiograph-

A

transmitted & scattered (both show up black) & absorbed (white, not talked ab a lot)

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5
Q

image-forming x-rays-

A

incident on IR

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6
Q

As SID decreases, what increases?

A

magnification

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7
Q

As kVp increases, what also increases?

A

-relative compton interaction
-scatter production

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8
Q

As kVp increases, what decreases?

A

-photoelectrons rapidly
-likelihood of any kind of single photon during a compton interaction

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9
Q

What does compton add to a radiograph?

A

fog/scatter

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10
Q

compton is scatter, but photons can-

A

scatter more than once

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11
Q

Why can you not use a low kVp technique?

A

-increases pt. dose
-would have fewer transmitted photons (black)

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12
Q

collimation reduces ____ ____ & improves ______.

A

reduces pt. dose & improves contrast

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13
Q

How does collimation help reduce scatter?

A

by restricting the beam

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14
Q

Field size affects-

A

amount of scatter produced

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15
Q

As field size increases, what also increases?

A

scatter

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16
Q

As field size increases, what decreases?

A

contrast

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17
Q

As patient thickness increases, what also increases?

A

scatter

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18
Q

with increasing pt. thickness, more x-rays undergo-

A

multiple scattering

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19
Q

What does pt. thickness result in?

A

greater average angle of scatter

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20
Q

What can be used to control patient thickness?

A

sometimes, compression devices

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21
Q

contrast-

A

visible difference between light & dark areas of an image

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22
Q

contrast resolution-

A

ability to image & distinguish the difference

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23
Q

as scatter increases, what decreases?

A

contrast

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24
Q

3 beam restrictors-

A

aperture diaphragm, cones & cylinders, & variable aperture collimator

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25
Q

Use a grid when part thickness gets above __, ___, or __. or when kVp is ____.

A

-when part thickness gets above 10, 12, or 13
-kVp is greater than 60

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26
Q

4 types of grids-

A

parallel, crosses, focused, & moving

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27
Q

2 reasons to use beam restrictors-

A

-only the tissue being examined should be exposed
-large field size increases scatter & decreases contrast

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28
Q

aperture diaphragm-

A

simplest & most restrictive beam restricting device (any kind of pitch aperture distorts it)

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29
Q

Aperture diaphragm is designed on film to-

A

leave 1 cm around field to prove collimation

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30
Q

What kind of construct is the aperture diaphragm?

A

lead/lead lined metal construct

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31
Q

aperture diaphragm opening is designed to be-

A

1 cm smaller on all sides of film

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32
Q

cones & cylinders is a modification to-

A

modification to aperture diaphragm

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33
Q

cones & cylinders resulting exposure-

A

resulting exposure is circular

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34
Q

cones & cylinders position & distal end determines-

A

field size

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35
Q

What is 1 problem with cones & cylinders?

A

cone-cutting

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36
Q

cone-cutting displayed by-

A

grid cut-off

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37
Q

What is the collimator also known as?

A

variable aperture diaphragm

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38
Q

collimator 1st stage-

A

enhances shutters designed to control off-focus radiation

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39
Q

collimator 2nd stage-

A

shutters work in pairs for square/rectangle fields

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40
Q

collimator allows for

A

infinite # of field sizes

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41
Q

collimator is more ___ & the least ____.

A

more versatile & the least __

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42
Q

collimator is the most commonly used-

A

most commonly used beam restrictor

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43
Q

PBL was mandated by-

A

US FDA for all x-ray machines in 1974

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44
Q

PBL was removed in 1994 bec-

A
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45
Q

bucky tray has sensors that detect-

A

size & alignment of cassette

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46
Q

synchronous motors are actuated to-

A

adjust to appropriate field size

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47
Q

even with PBL, tighter collimation will-

A

reduce pt. exposure

48
Q

the grid is used to-

A

remove scattered x-ray after the subject & before IR

49
Q

the grid was firs demonstrated by-

A

gustaf bucky in 1913

50
Q

the grid consists of-

A

series of alternating radiopaque & radiolucent materials

51
Q

radiopaque materials are-

A

led

52
Q

radiolucent materials are-

A

plastic/carbon

53
Q

radiopaque strips are called-

A

grid strips

54
Q

radiolucent strips are called-

A

interspace material

55
Q

grid ratio formula-

A

height of led strips divided by width of interspace (H/D)

56
Q

high-ratio grids are more effective at-

A

“cleaning up” scattered x-rays

57
Q

grids range from-

A

5:1-16:1

58
Q

5:1 ____ cleanup-

A

85%

59
Q

16:1 _____ cleanup=

A

97%

60
Q

grids take ____ away where it shouldn’t be & adds ____.

A

takes away black, adds white

61
Q

scatter puts ____ where ____ should be-

A

puts black where white should be

62
Q

grid frequency-

A

Number of grids per cm/inch

63
Q

high frequency grids show-

A

less distinct grid lines than low frequency grid

64
Q

frequency is increased by-

A

adding grid strips & thinning interspace material

65
Q

purpose of interspace material-

A

maintain precise separation b/w delicate led strips

66
Q

aluminum advantages-

A

-less visible grid lines
-nonhygroscopic
-easier to manufacture precise specifications

67
Q

non hygroscopic-

A

doesn’t attract water molecules

68
Q

interspace materials used are-

A

aluminum or plastic fiber (neither preferred, they do ab the same)

69
Q

aluminum disadvantages-

A

-absorption of primary beam resulting in higher pt. dose as mAs is compensated
-at low kVp, pt. dose may be increased by up to 20%

70
Q

grid casing is primarily made of-

A

aluminum or plastic

71
Q

grid casing provides-

A

rigidity & helps seal out moisture

72
Q

grid casing helps-

A

maintain cassette contact & protects grid

73
Q

grid casing job-

A

hold precise manufactured grid strips together in its proper place & seals out moisture from getting in

74
Q

contrast improving factor (k)-

A

ratio of contrast of a radiograph w: grid to the contrast of radiograph made w/o grid

75
Q

k for most grids-

A

b/w 1.5 & 2.5

76
Q

bucky factor (B) also called-

A

grid factor

77
Q

bucky factor (B) increase in-

A

amt. of technique required to achieve the same receptor exposure on a radiograph

78
Q

bucky factor (B) increases-

A

pt. dose

79
Q

parallel grid properly used-

A

results in grid cut off on lateral margins

80
Q

in a parallel grid, why doesn’t grid cut-off occur on top & bottom?

A

beam divergence doesn’t’t cross grid lines

81
Q

optical density decreases towards-

A

edges

82
Q

parallel grids more pronounced at-

A

short SID

83
Q

parallel grids clean up scatter-

A

in only 1 direction

84
Q

cross/cross hatch grids clean up scatter-

A

in all directions

85
Q

2 serious disadvantages of cross/cross hatch grids-

A

-positioning in critical
-any tube angle against grid will produce grid cut-off

86
Q

focused grids designed to-

A

minimize grid cut-off

87
Q

focused grids when used properly-

A

grid cut-off not visible

88
Q

focused grids are marked with-

A

intended focus distance & which side of grid faces tube

89
Q

in focused grids, led strips are angled to-

A

match beam divergence

90
Q

Dr.Hollis improved on Bucky’s grid by-

A

moving grid during exposure

91
Q

moving grids are called-

A

potter-bucky diaphragm

92
Q

2 types of moving grids-

A

-reciprocating (to & fro movement)
-oscillating (circular motion)

93
Q

disadvantaged of moving grids-

A

increased OID, increased image blur, & bulkiness of mechanics

94
Q

virtual grids are-

A

reconstructions of captured data

95
Q

virtual grids algorithms can-

A

identify scatter & remove their effect from radiograph

96
Q

virtual grids lead to-

A

lower pt. dose w: high quality images

97
Q

most common problem of grids-

A

improper positioning

98
Q

off-level grid-

A

most often caused by tube head mis-positioning

99
Q

off-level & off-center grids are

A

the same thing

100
Q

off center grid, tube is off center ___ & called ____ _____.

A

off center laterally, called lateral decentering

101
Q

off-center grid causes grid cut-off along-

A

entire radiograph

102
Q

off-focus grid is a focused grid using-

A

wrong SID

103
Q

off-center grids are further from focus distance the more-

A

severe the grid cut-off

104
Q

grid cut-off is more severe toward-

A

periphery (edges)

105
Q

off center grids have to have-

A

what side is toward the tube & what the focal distance is

106
Q

upside down grid-

A

if turn grid upside down, entire grid is an x-ray catcher

107
Q

proper grid ratio selection depends on 3 things-

A

-kVp increases, grid ratio should increase
-degree of clean up increases as ratio increases
-pt. dose in general- as ratio increases, dose increases

108
Q

pt. radiation dose increases w:-

A

increasing grid ratio

109
Q

high-ratio grids are used with-

A

high kVp exams

110
Q

pt. radiation dose at ____ ____ is less than at ____ ____.-

A

at high kVp is less than @ low kVp

111
Q

air-gap technique-

A

method of removing radiation scatter w/o using grid

112
Q

air-gap technique is an alternative to-

A

grids

113
Q

air-gap technique increases-

A

OID to 10-15 cm

114
Q

air-gap technique allows scattered x-rays to-

A

miss IR

115
Q

disadvantage of air-gap technique-

A

increase magnification & loss of recorded detail

Radt. 3011 (13 decks)

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