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Rad105 > Test 4 - CH 12, 13 > Flashcards

Test 4 - CH 12, 13 Flashcards

1
Q

What is the primary result of Compton interactions?

A

scatter

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2
Q

two major factors that affects the amount of scatter radiation produced and exiting the patient

A

volume of tissue irradiated
kVp

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3
Q

the volume of tissue depends on what two things?

A

part thickness
x-ray beam field size

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4
Q

what decreases the x-ray field size and the amount of tissue irradiated?

A

beam-restricting devices

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5
Q

what is used to improve image quality by absorbing scatter that exits the patient

A

grids

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6
Q

(T/F) grids reduce scatter in the patient

A

false
- only reduces the scatter that reaches the IR

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7
Q

beam restriction limits what and reduces what?

A

limits patient exposure
- reduces amount of scatter radiation produced w/i patient

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8
Q

what changes the shape and size of the primary beam?

A

beam-restricting devices

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9
Q

increasing collimation does what to the field size?

A

decreases field size

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10
Q

beam restriction does what to contrast?

A

increase

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11
Q

for collimation, quantum noise increases so what has to be adjusted?

A

mAs

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12
Q

what happens to quantum noise when field size increases?

A

decreases

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13
Q

when going from a 14x17 IR to a 8x10, what should be done to mAs

A

double

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14
Q

a flat piece of lead (diaphragm) that has a hole (aperture) in it and is placed directly below the x-ray tube

A

aperture diaphragm

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15
Q

where is an aperture diaphragm placed?

A

under collimator

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16
Q

what is caused from the aperture diaphragm because of its close proximity to the radiation source

A

large area of unsharpness on the edges

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17
Q

an aperture diaphragm with an extended flange attached to it

A

cone or cylinder

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18
Q

cones and cylinders are slid onto the tube where?

A

directly below the window

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19
Q

cones and cylinders does what to sharpness around the image

A

limit

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20
Q

which is more useful, cones or cylinders

A

cylinders

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21
Q

(T/F) cones and cylinders are almost always made to produce a circular projected field

A

true

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22
Q

what is considered the best beam-restricting device

A

collimators

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23
Q

where is a collimator located? and consists of what?

A

below tube window
-lead shutters

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24
Q

what are collimators equipped with?

A
  • white light source
  • mirror
  • measurement
  • crosshairs
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25
Q

what automatically limits the size and shape of the primary beams to the size and shape of the IR

A

automatic collimators
- positive beam-limiting (PBL)

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26
Q

(T/F) with a PBL you are allowed to go larger than the IR

A

false

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27
Q

devices that have very thin lead strips with radiolucent interspaces, intended to absorb scatter emitted from the patient

A

radiographic grids

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28
Q

in grids, lead lines and interspace material is covered by what?

A

aluminum front and back panel

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29
Q

Grid ration formula

A

height / width of interspace

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30
Q

grid patterns

A

linear: lead lines run in 1 direction
cross-hatched: lines run at right angles

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31
Q

lead line orientation:
nonfocused and focused grid

A

nonfocused: lead lines run parallel
focused: lead lines are angled to match divergence of beam

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32
Q

(T/F) nonfocused grids allow more transmitted photons to reach IR

A

false
focused

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33
Q

the convergent point/line determines what?

A

the focal distance of a focused grid

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34
Q

distance between the grid and the convergent line or point

A

focal distance (grid radius)

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35
Q

what is the focal range

A

recommended range of SID that can be used with a focused grid

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36
Q

stationary are what type of grids and examples (2)

A

nonmoving
-cassette : grid attached to IR permanently
-cap: permanently mounted grid and allows the IR to slide behind it

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37
Q

(T/F) when grids are stationary it’s possible to see grid lines on the radiographic image

A

true

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38
Q

example of moving/reciprocating grids

A

potter-bucky diaphragm: below table-top and above the tray that holds IR

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39
Q

grid motion is controlled by the what?

A

x-ray exposure switch

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40
Q

grids move slightly back and forth in a ______ direction over the IR during the ____ exposure

A

lateral
entire

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41
Q

short-dimension grids run ___ to the long axis, long lead strips run ___ to the long axis

A

perpendicular
parallel

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42
Q

a decrease in the number of transmitted photons that reach the IR because of some misalignment of the grid

A

grid cutoff

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43
Q

when does an upside-down focused grid cutoff occur?

A

when a grid is placed upside down on the IR
-results in grid line going opposite the angle of divergence

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44
Q

off-level grid cutoff occurs when

A

when the x-ray beam is angled across the lead

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45
Q

off center grid cutoff occurs when

A

when the CR of the beam is not aligned with the center of a grid

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46
Q

off-focus grid cutoff occurs when

A

when using an SID outside of the recommended focal range

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47
Q

(T/F) off focus grid cutoff radiographically look different, whether it’s being too close or too far away

A

false
look the same

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48
Q

what is the Moiré effect, how is it caused?

A

zebra pattern artifact that can occur when a stationary grid is used during CR imaging, caused by the grid frequency being similar to the laser scanning frequency

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49
Q

grid selection involves consideration of what 3 things?

A

contrast improvement
patient dose
likelihood of grid cutoff

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50
Q

air gap technique is based on what?

A

increased OID

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51
Q

(T/F) placing a lead shield on the x-ray table absorbs scatter radiation

A

true

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52
Q

Does using a lead blocker decrease pt dose? why?

A

No, only absorbing scatter that already left the pt

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53
Q

what is AEC?

A

automatic exposure control
-used to control the amount of radiation reaching the IR by terminating the length of the exposure

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54
Q

what factors does the tech set when using AEC?

A

kVp, mA, IR, grid

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55
Q

AEC is excellent at producing what when used properly?

A

consistent levels of exposure

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56
Q

How does AEC system know when to terminate the exposure?

A

uses radiation detectors that takes the radiation transmitted through the patient and converts it into an electrical signal

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57
Q

two types of AEC

A

phototimers: 1st gen
ionization chambers: more common

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58
Q

How many radiation detectors are there and what is the techs role with them?

A

3
-tech chooses which ones to activate

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59
Q

Phototimer AEC devices uses what to convert light to electricity?

A

fluorescent screen and a device

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60
Q

a photomultiplier (PM) tube is a device that converts what?

A

visible light energy into electrical energy

61
Q

a solid-state device that performs the same function

A

photodiode

62
Q

with exit-type devices, what serves as the detectors?

A

light paddles coated with fluorescent material

63
Q

with exit-type devices, how is the timer tripped?

A

when radiation interacts with the paddles it produces light, which is then converted to electricity

64
Q

which is used more, exit or entrance type devices? examples of both?

A

entrance more used
exit = phototimer
entrance = ionization chamber

65
Q

with entrance-type devices, how is the timer tripped?

A

when exposed to radiation, the air in the chambers becomes ionized, creating an electrical charge, it travels along the wire to the timer circuit

66
Q

mAs readout / second readout is what?

A

the actual amount of mAs used for that image

67
Q

the kVp level selected must be at least what?

A

at least the minimum kVp to penetrate the part

68
Q

using higher kVp does what to exposure time and overall mAs needed?

A

decreases
decreases

69
Q

increasing mA on the control panel does what to exposure time?

A

decreases/shortens
(opposite is true)

70
Q

(T/F) minimum response time refers to the longest time that the system can produce?

A

false
shortest time

71
Q

minimum response time with modern AEC is what?

A

1 ms

72
Q

(T/F) minimum response time is usally longer with AEC systems than with other types of radiographic timers

A

true

73
Q

what refers to the maximum length of time the x-ray exposure will continue when using an AEC system?

A

Backup time

74
Q

(T/F) backup time is a safety mechanism when an AEC fails or the equipment isn’t used properly

A

true

75
Q

what allows the radiographer to adjust the amount of preset radiation detection values?

A

exposure adjustment (density controls)

76
Q

regularly using _______ settings to produce an acceptable image indicates that a problem exists

A

plus or minus exposure adjustment

77
Q

what chambers/detectors do you choose?

A

ones that will be superimposed by the anatomic structures of greatest interest

78
Q

failure to use the proper detectors could result in what?

A

underexposure or overexposure to the IR

79
Q

(T/F) failure to select the correct bucky can result in the pt and IR being exposed to excessive radiation

A

true

80
Q

improper centering may result in what?

A

underexposure/overexposure to the IR

81
Q

(T/F) AEC size can be adjusted

A

false
- fixed and can’t be adjusted

82
Q

what should you do if the detector combination is larger than the area of interest?

A

use a manual exposure technique

83
Q

how does the AEC compensate for patient thickness?

A

if thicker, the exposure time will lengthen to reach the preset exposure

84
Q

what may require greater technical consideration when using AEC?

A

excessive bowel gas
destructive pathologic conditions
postive contrast media

85
Q

how is collimation a factor in AEC systems
no collimation vs close collimation

A
  • can cause the exposure to be terminated
  • could overexpose the pt
86
Q

what does the AEC do when anatomically programmed techniques are used in conjunction with AEC?

A
  • selects and displays manual expo factors
  • selects and displays AEC detectors to be used
87
Q

what are essential procedures to maintain the proper functioning of the AEC

A

calibration and QC

88
Q

how can AEC performance be monitored?

A

by imaging a homogenous pt equiv. phantom with additional thickness plates

89
Q

what are preestablished guidelines used to select standardized manual / AEC exposure factors for each type of exam?

A

exposure technique charts

90
Q

what 3 things do exposure technique charts do

A

produce consistent quality images
reduces repeat radiograph studies
reduce patient exposure

91
Q

for technique charts to be effective, what should be established and what must operate properly?

A

quality standards
radiographic system

92
Q

devices that measure part thickness

A

caliper

93
Q

where can you find the exact location for measuring part thickness?

A

technique chart

94
Q

(T/F) the primary expo. factors of kVp and mAs and Ir type, grid ration are included regardless of the type of technique chart used?

A

true

95
Q

two types of technique charts

A

variable - fixed mAs
fixed kVp - variable mAs

96
Q

chart that is based on the concept that kVp can be increased as the anatomic part size increases

A

variable kVp - fixed mAs

97
Q

what is critical to the efficacy of the variable kVp chart?

A

accurate measurement of part thickness

98
Q

(T/F) determination of the baseline kVp for each anatomic area has been standardized

A

false
not been standardized

99
Q

chart that uses the concept of selecting an optimal kVp that is required for the exam and adjusting the mAs for variations in part thickness

A

fixed kVp - variable mAs

100
Q

what is kVp that is high enough to ensure penetration of the part but not too high to diminish radiographic contrast?

A

optimal kVp

101
Q

(T/F) optimal kVp required for each anatomic area has not been standardized

A

true

102
Q

once optimal kVp is established fixed kVp - variable mAs charts alter what?

A

the mAs for variations in part thickness

103
Q

(T/F) using higher kVp ranges with DR systems can reduce the variability among exposure techniques for the same / similar regions

A

true

104
Q

primary tools needed to develop a exposure technique chart

A

caliper
phantoms
calculator

105
Q

this concept states that different parts of the same size can be imaged by use of the same expo factors, provided that the kVp needed to penetrate the part is used

A

comparative anatomy

106
Q

(T/F) pediatric patients require high kVp and low mAs compared to adults

A

false
low kVp

107
Q

lower bone density may require what in exposure?

A

reduction

108
Q

(T/F) geriatric patients may need an increase in exposure techniques

A

false

109
Q

(T/F) geriatric patient may need an increase in kVp and mAs, grids, and imaged in quadrants

A

true

110
Q

(T/F) diff projections and positions of the same part don’t often require modification of exposure factors

A

false
do require modification

111
Q

fiberglass and plaster casts require what?

A

fiberglass = no change
plaster = increase

112
Q

inflatable, fiberglass, wood, aluminum, and solid plastic splints require what?

A

inflatable and fiberglass = no change
everything else may be increased if it’s in the path of the primary beam

113
Q

diseases or conditions
- that increases the absorption of the part

  • that decreases the absorption of the part
A

additive
destructive

114
Q

contrast media is used when anatomic tissues have what subject contrast?

A

low

115
Q

contrast agent that
- produces more brightness
- produces less brightness

A

positive
negative

116
Q

When going from a 11x14 field size to a small 4in cone, what must be increased and why?

A

Increase exposure
Need to compensate for the decrease in the number of X-ray photons that otherwise occur

117
Q

Simplest type of beam restricting device

A

Aperture diaphragm

118
Q

Can you adjust the field size with an aperture diaphragm?

A

No it’s a set size

119
Q

Which beam restricting device has the least amount of area of unsharpness

A

Cones and cylinders

120
Q

Grids are usually used when part thickness is what and kVp is higher than what?

A

Party thickness is greater than 10cm
KVp greater than 60

121
Q

Increasing grid ratio for the same grid frequency will increase what two things

A

Increase the amount of lead content
Increase scatter absorption

122
Q

If you increase grid frequency and use the same grid ratio, there is less what because why?

A

Less lead content
- width of the interspace or thickness of the lead have been decreased

123
Q

Decreasing the overall lead content will result in what?

A

Decreased scatter absorption

124
Q

Which grid pattern absorbs more scatter and why

A

Crossed grids
- contains more lead strips that are in two directions

125
Q

Can you angle the X-ray tube when using a crossed grid

A

No
Grid cutoff

126
Q

Which type of grid (focused/non focused) allows more transmitted photons?

A

Focused

127
Q

What grid matches the size of the cassette and is used by placing it on top of the IR

A

Wafer grid

128
Q

How do the grid lines get blurred when using a stationary grid

A

Its slightly moved laterally (back and forth) during the entire X-ray exposure

129
Q

GCF formula

A

mAs with grid / mAs without grid

130
Q

What grid cutoff occurs with both focused and parallel grids

A

Off level
- X-ray beam is angled

131
Q

What can help eliminate the moire effect from happening

A

Higher grid frequency or moving grid

132
Q

What describes the number of lead lines per unit length

A

Grid frequency

133
Q

(T/F) difference in AEC systems lies in the type of device used to convert radiation into electricity

A

True

134
Q

When the detectors are positioned behind the IR vs in front of the IR

A

Exit type device
Entrance type device

135
Q

Setting the backup time _________ of the expected exposure time is appropriate

A

150-200%

136
Q

Is the detector able to distinguish transmitted radiation from scattered?

A

No

137
Q

(T/F) IRs cannot be interchanged easily since the AEC is calibrated to terminate exposure levels at a preset level

A

True

138
Q

What ensures the consistent and appropriate exposures to the IR are produced

A

Calibration

139
Q

An X-ray generator should always have the same level of radiation exposure no matter what technical factors are set
Max variable variation

A

Reproducibility of the exposure
+- 5%

140
Q

Variations between the state kVp and the X-ray beam quality must be within

A

+- 5%

141
Q

QC checks used to determine kVp accuracy

A

Wisconsin test tool: holes in the IR
Digital kVp meter

142
Q

Exposure time directly affects the total quantity of radiation emitted from tube

A

Timer accuracy QC
+- 5% for over 10ms

+- 20% for less 10ms

143
Q

The same mAs using different mA and time combinations should produce the same radiation output

A

Reciprocity law
+- 10%

144
Q

Sequential increases in mAs should produce the same sequential increases in exposure

A

Linearity
+- 10%

145
Q

Focal spot size variation
Percent of blooming allowable for:
0.8 mm or less, 0.8mm to 1.5mm, 1.6mm or greater

A

50%
40%
30%

146
Q

How well the collimator regulates the field size and area that is illuminated on the IR

A

Light field radiation fells congruence QC
+- 2%

147
Q

Center of the bucky tray must be centered to the X-ray beam

A

X-ray beam bucky alignment QC
Within 1% of the SID

148
Q

All medical X-ray units must be equipped with a SID indicator

A

SID indicator QC
+- 2%

Rad105 (6 decks)

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