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MRT > DI quiz 3 - AEC > Flashcards

DI quiz 3 - AEC Flashcards

1
Q

With AEC, you never select what ?

A

time - mAs (because AEC controls the time based on how long it takes to receive adequate radiation)

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2
Q

What is AEC?

A

automatic exposure control - automatically adjusts the amount of radiation used

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3
Q

What 2 things are important when using AEC?

A

anticipated values and actual values

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4
Q

Main purpose of AEC?

A

To ensure patient isn’t overexposed to radiation and image produced has the right level of brightness / detail (regardless of thickness) and provide consistency with exposures

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5
Q

Location of AEC with normal digital radiography?

A

BEFORE IR

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6
Q

What happens once AEC detectors sense that enough radiation has been received to create a good-quality image?

A

The exposure is terminated (send signal)

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7
Q

Pros of AEC

A

provides consistency (because x-ray tech isn’t picking a technique) and reduces overexposure risk to pt

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8
Q

In order for AEC to work correctly, it’s important to:

A

properly center / position patient to correct detectors and select correct detectors (alignment*)

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9
Q

Which detector do you always centre to?

A

center detector

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10
Q

Purpose of exposure adjustment switch? (density selector)

A

extend (lengthen) or shorten the exposure more than it normally would

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11
Q

With exposure adjustment, what occurs at the positive side? (+)

A

Will go past the cut off, it will make the exposure longer (extend)

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12
Q

With exposure adjustment, what occurs at the negative side? (-)

A

Won’t go all the way to the cut off, it will terminate the exposure sooner

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13
Q

Why are exposure adjustments only with AEC?

A

You don’t extend or shorten with fixed techniques (the technique is what it is with fixed technique)

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14
Q

What is “fixed mode”

A

algorithm doesn’t fix the image - image stays the same (similar to raw data - can be dark)

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15
Q

What is the purpose of algorithm?

A

to adjust image after exposure

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16
Q

When would we use exposure adjustment / density selectors? (when would you want to shorten/lengthen exposure)

A

high (larger pt) or low (smaller pt) scatter situations (ex. larger body part - large pt, large abdomen, larger pelvis)

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17
Q

Do IR and AEC communiate?

A

no

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18
Q

What doesn’t AEC know?

A

if you properly positioned/centered patient, the difference between good or bad (scatter) radiation

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19
Q

Larger field size sees more?

A

scatter = IR sees more radiation = shorter exposure time = lower mAs

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20
Q

Imaging a larger body part will lead to

A

longer exposure time, higher mAs

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21
Q

What is always an option with AEC?

A

turning it off and going to a fixed technique, use exposure adjustments (the +/-)

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22
Q

When are exposure adjustment / density selectors done - before or after exposure?

A

before exposure

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23
Q

Using small focal spot with AEC, what do you need to be cautious about?

A

you’ll be using a longer time to get the mAs (if you’re doing a exp that motion is an issue - can be an issue)

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24
Q

Limitations of AEC? Shouldn’t use AEC:

A

if anatomy doesn’t cover cells, with peripheral anatomy (anatomy near outside of body-clavicle), if pt has radiopaque material (hip replacement)

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25
Q

AEC won’t compensate for

A

bad centring / positioning

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26
Q

Why is using AEC with radiopaque material not good?

A

the metal material has higher atomic Z / more dense, AEC detector will see less radiation = longer exp and higher mAs

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27
Q

Improper centring can cause

A

underexposure (because AEC will call for a shorter exp time based on centring of anatomy), premature image/cut off, changes in mAs and DI

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28
Q

What indicates you may need to retake an image?

A

looking at the image (not the DI)

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29
Q

What is the most repeated?

A

chest x-ray

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30
Q

Be cautious with what gender for chest xray, and why?

A

female - because breast tissue is more dense, so will absorb more radiation

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31
Q

What does AEC control?

A

the exposure time (exposure will terminate once adequate radiation received)

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31
Q

What is an anticipated value with AEC?

A

What value/mAs you’re expecting to see

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32
Q

What is an actual value with AEC?

A

What the value/mAs actually was after exposure

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33
Q

Why is it important to look at mAs after exposure with AEC?

A

To know how much radiation pt received and to compare the anticipated/actual value

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34
Q

Why are the outlines not on the table?

A

because the table floats and IR moves with the upright bucky

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35
Q

What type of radiation does AEC measure?

A

remnant radiation

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36
Q

How much radiation needs to hit IR for a good image

A

1 mR

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37
Q

What is AEC detector inbetween?

A

grid and IR

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38
Q

With AEC, regardless of pt thickness, IR should

A

receive the same amount of radiation, might just take longer for thicker body (same rad needed for a good image for that body part)

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39
Q

Why does a thicker body part take longer?

A

because thicker body part absorbs more radiation = less radiation per time reaching IR = longer exposure time

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40
Q

When does AEC compensate for changes in radiation intensity?

A

If it occurs prior to detector, NOT after detector

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41
Q

What does AEC use for their detectors?

A

ionization chambers

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42
Q

Explain ionization chamber purpose in AEC

A

x-ray photons hit the ionization chamber, creating a charge, once a certain amount of radiation has reached, signal is sent, and exposure is terminated

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43
Q

What techniques do you select with AEC?

A

kvp and mA

44
Q

Purpose of ionization chambers

A

to measure the radiation

45
Q

What happens with a small pt / body part regarding AEC?

A

AEC will shut down (terminate) exposure sooner, shorter exposure time and lower mAs

46
Q

What happens with a large pt / body part regarding AEC?

A

AEC will take longer to shut down (terminate), longer exposure time and higher mAs

47
Q

What detectors do you select for spine

A

center

48
Q

What detectors do you select for abdomen

A

all 3

49
Q

What detectors do you select for chest

A

R / L lateral

50
Q

What anatomy shouldn’t you use AEC with?

A

clavicle, lateral Y scapula, patella, mandible, sternum and any anatomy that won’t cover the entire detector (ex. finger)

51
Q

Important factors for using AEC

A

collimation, anatomy knowledge, proper position/centring, technique understanding

52
Q

When would you use: center detector

A

80% of the time - Shoulder, spine, hip, femur, skull work, single knee, lateral chest

53
Q

When would you use: lateral detector

A

Standing knees, chest AP/PA

54
Q

When would you use: all 3 detectors

A

Abdomen, pelvis area

55
Q

IR gets a fixed amount of radiation regardless of the following

A

kVp, mA, SID, pt thickness

56
Q

Define minimum response time

A

shortest possible exposure time (only with AEC)

57
Q

Purpose of having a back up mAs (time) with AEC?

A

System failure, Technologist error

58
Q

What does having a back up mAs with AEC prevent?

A

accidentally overexposing patient and prevents tube overload

59
Q

Backup mAs (time) rule of thumb?

A

1.5 – 2x the expected manual exposure time / mAs

60
Q

Pro of having a back up mAs option with AEC

A

it can be changed

61
Q

Con of having a back up mAs option with AEC

A

it can terminate sooner / quicker, has to be selected first

62
Q

What happens with image if not properly collimated with AEC?

A

longer exposure time because the detectors aren’t in the proper collimation

63
Q

Explain falling load

A

starts the exposure with highest mA for selected kvp - mA drops during exposure (so, mA is always changing)

64
Q

What do you select with falling load?

A

kvp

65
Q

What does the falling load ensure? with mA

A

that the highest possible mA is used for the shortest exposure time allowed (maximizes mA)

66
Q

Reasons why underexposure would occur with AEC

A

Back-up time less than needed exposure time, density left on the minus setting, Improper collimation (scatter), Incorrect detector cell selection, Detector cell not completely covered by area (tissue) of interest

67
Q

Factors that are important to consider when using AEC for chest

A

Gender, body habitus, heart, diaphragm, centered up high enough, correct detectors, full inspiration

68
Q

Issue with detectors being too low with AEC

A

will have a longer exposure time and higher mAs because of diaphragm and heart being in the way

69
Q

Reasons why overexposure would occur with AEC

A

Needed exposure time less than MRT, Density left on plus setting (higher mAs), Incorrect detector cell selection, Radiopaque material, Electronic malfunction

70
Q

Detector cell not completely covered by area (tissue) of interest can cause

A

lower mAs

71
Q

Will AEC compensate for filtration?

A

yes, filters occur before detector

72
Q

What does back up time set up?

A

the MAX exposure time (MAX mAs)

73
Q

What do you select with AEC technique wise?

A

kvp, mA (can be adjusted)

74
Q

List what you select for AEC, on the monitor?

A

grid, kvp, mA, IR type, detector

75
Q

Do we know our mAs prior to our exposure with AEC?

A

no, because mAs is determined after the exposure with mAs

76
Q

What can you do if you don’t know what your anticipated mAs will be for an exposure?

A

switch to a fixed technique to see what your mAs value should be after exposure

77
Q

Why wouldn’t you use AEC for a finger?

A

because a finger doesn’t completely cover the AEC detector (large area around the finger - IR will see a LOT of radiation)

78
Q

What exposure time would a 180 cm SID have?

A

longer - because less radiation reaching IR and less intensity

79
Q

exposure time between 50 mA and 500 mA

A

50 mA would have longer exposure time

80
Q

Will AEC compensate for thicker / thinner patient?

A

yes, may just take longer / shorter time

81
Q

With AEC, regardless of SID or patient thickness, in the end IR should _________________

A

see the same amount of radiation, might just take longer or shorter time

82
Q

With grids, going from 8:1-12:1 ratio, what happens?

A

12:1 absorbs more x-ray photons so longer exposure time until proper radiation received

83
Q

What does improper detector selection do?

A

provides inaccurate amount of radiation for image, can cause longer exposure time

84
Q

Detectors are designed for?

A

consistent exposures / intensity, fewer repeats

85
Q

Once ion capacitor (ion chamber) is charged, what happens?

A

exposure terminates

86
Q

look at mAs value when during AEC?

A

after exposure

87
Q

Would AEC compensate for an extra grid left on the IR by mistake during an exposure?

A

no, because the extra grid on the IR comes AFTER the exposure

88
Q

If you were to image a finger using AEC, what would happen?

A

detector would see a lot of radiation

89
Q

Using the two lateral detectors, do they see the same radiation or different?

A

50/50 (same)

90
Q

What would happen if you were off center with AEC and soft tissue was an issue?

A

increased radiation exposure to IR = shorter exposure time than needed

91
Q

What would happen if you were off center with AEC detector for chest and you centered over the spine?

A

Spine absorbs more radiation so higher mAs and longer exposure time

92
Q

How will overexposure affect mAs?

A

will be higher than anticipated value

93
Q

How will underexposure affect mAs?

A

will be lower than anticipated value

94
Q

“fixed” image is the

A

raw data

95
Q

Why 3 detectors with abdomen?

A

helps average out abdomen since there’s a lot of organs, ST, air, gas

96
Q

Issue with using AEC with barium?

A

detectors may be under barium (similar to metal)

97
Q

Purpose of filters?

A

get rid of low E photons

98
Q

Will AEC compensate for filtration?

A

yes, because it’s before the AEC detector

99
Q

Will AEC compensate for new IR having a different DQE?

A

No, because that doesn’t occur before the IR

100
Q

When anatomy is over less dense anatomy than needed, what happens to the image?

A

underexposure

101
Q

When anatomy is over more dense anatomy than needed, what happens to the image?

A

overexposure

102
Q

Purpose of falling load

A

to give us shorter exposure times

103
Q

How do you shorten exposure with falling load?

A

go from 80% setting to 100% setting

104
Q

If you’re concerned with motion and you’re using falling load with AEC, would you use 80% setting or 100% setting?

A

100% to get shorter time

105
Q

what is the minimum response time

A

shortest exposure time possible with AEC

106
Q

What causes changes in mAs (DI stays the same)

A

lateral decentering, increased SID, filtration, grid

107
Q

What causes changes in mAs and DI

A

Improper centering, scatter, field size, wrong AEC detector, back up time, density selection

108
Q

If you have to repeat an image after using AEC, what should you do?

A

use a fixed technique (UNLESS you know why - example: picked the wrong AEC detector)

MRT (12 decks)

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