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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
AEC won't compensate for
bad centring / positioning
26
Why is using AEC with radiopaque material not good?
the metal material has higher atomic Z / more dense, AEC detector will see less radiation = longer exp and higher mAs
27
Improper centring can cause
underexposure (because AEC will call for a shorter exp time based on centring of anatomy), premature image/cut off, changes in mAs and DI
28
What indicates you may need to retake an image?
looking at the image (not the DI)
29
What is the most repeated?
chest x-ray
30
Be cautious with what gender for chest xray, and why?
female - because breast tissue is more dense, so will absorb more radiation
31
What does AEC control?
the exposure time (exposure will terminate once adequate radiation received)
31
What is an anticipated value with AEC?
What value/mAs you're expecting to see
32
What is an actual value with AEC?
What the value/mAs actually was after exposure
33
Why is it important to look at mAs after exposure with AEC?
To know how much radiation pt received and to compare the anticipated/actual value
34
Why are the outlines not on the table?
because the table floats and IR moves with the upright bucky
35
What type of radiation does AEC measure?
remnant radiation
36
How much radiation needs to hit IR for a good image
1 mR
37
What is AEC detector inbetween?
grid and IR
38
With AEC, regardless of pt thickness, IR should
receive the same amount of radiation, might just take longer for thicker body (same rad needed for a good image for that body part)
39
Why does a thicker body part take longer?
because thicker body part absorbs more radiation = less radiation per time reaching IR = longer exposure time
40
When does AEC compensate for changes in radiation intensity?
If it occurs prior to detector, NOT after detector
41
What does AEC use for their detectors?
ionization chambers
42
Explain ionization chamber purpose in AEC
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
43
What techniques do you select with AEC?
kvp and mA
44
Purpose of ionization chambers
to measure the radiation
45
What happens with a small pt / body part regarding AEC?
AEC will shut down (terminate) exposure sooner, shorter exposure time and lower mAs
46
What happens with a large pt / body part regarding AEC?
AEC will take longer to shut down (terminate), longer exposure time and higher mAs
47
What detectors do you select for spine
center
48
What detectors do you select for abdomen
all 3
49
What detectors do you select for chest
R / L lateral
50
What anatomy shouldn't you use AEC with?
clavicle, lateral Y scapula, patella, mandible, sternum and any anatomy that won't cover the entire detector (ex. finger)
51
Important factors for using AEC
collimation, anatomy knowledge, proper position/centring, technique understanding
52
When would you use: center detector
80% of the time - Shoulder, spine, hip, femur, skull work, single knee, lateral chest
53
When would you use: lateral detector
Standing knees, chest AP/PA
54
When would you use: all 3 detectors
Abdomen, pelvis area
55
IR gets a fixed amount of radiation regardless of the following
kVp, mA, SID, pt thickness
56
Define minimum response time
shortest possible exposure time (only with AEC)
57
Purpose of having a back up mAs (time) with AEC?
System failure, Technologist error
58
What does having a back up mAs with AEC prevent?
accidentally overexposing patient and prevents tube overload
59
Backup mAs (time) rule of thumb?
1.5 – 2x the expected manual exposure time / mAs
60
Pro of having a back up mAs option with AEC
it can be changed
61
Con of having a back up mAs option with AEC
it can terminate sooner / quicker, has to be selected first
62
What happens with image if not properly collimated with AEC?
longer exposure time because the detectors aren’t in the proper collimation
63
Explain falling load
starts the exposure with highest mA for selected kvp - mA drops during exposure (so, mA is always changing)
64
What do you select with falling load?
kvp
65
What does the falling load ensure? with mA
that the highest possible mA is used for the shortest exposure time allowed (maximizes mA)
66
Reasons why underexposure would occur with AEC
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
Factors that are important to consider when using AEC for chest
Gender, body habitus, heart, diaphragm, centered up high enough, correct detectors, full inspiration
68
Issue with detectors being too low with AEC
will have a longer exposure time and higher mAs because of diaphragm and heart being in the way
69
Reasons why overexposure would occur with AEC
Needed exposure time less than MRT, Density left on plus setting (higher mAs), Incorrect detector cell selection, Radiopaque material, Electronic malfunction
70
Detector cell not completely covered by area (tissue) of interest can cause
lower mAs
71
Will AEC compensate for filtration?
yes, filters occur before detector
72
What does back up time set up?
the MAX exposure time (MAX mAs)
73
What do you select with AEC technique wise?
kvp, mA (can be adjusted)
74
List what you select for AEC, on the monitor?
grid, kvp, mA, IR type, detector
75
Do we know our mAs prior to our exposure with AEC?
no, because mAs is determined after the exposure with mAs
76
What can you do if you don't know what your anticipated mAs will be for an exposure?
switch to a fixed technique to see what your mAs value should be after exposure
77
Why wouldn't you use AEC for a finger?
because a finger doesn't completely cover the AEC detector (large area around the finger - IR will see a LOT of radiation)
78
What exposure time would a 180 cm SID have?
longer - because less radiation reaching IR and less intensity
79
exposure time between 50 mA and 500 mA
50 mA would have longer exposure time
80
Will AEC compensate for thicker / thinner patient?
yes, may just take longer / shorter time
81
With AEC, regardless of SID or patient thickness, in the end IR should _________________
see the same amount of radiation, might just take longer or shorter time
82
With grids, going from 8:1-12:1 ratio, what happens?
12:1 absorbs more x-ray photons so longer exposure time until proper radiation received
83
What does improper detector selection do?
provides inaccurate amount of radiation for image, can cause longer exposure time
84
Detectors are designed for?
consistent exposures / intensity, fewer repeats
85
Once ion capacitor (ion chamber) is charged, what happens?
exposure terminates
86
look at mAs value when during AEC?
after exposure
87
Would AEC compensate for an extra grid left on the IR by mistake during an exposure?
no, because the extra grid on the IR comes AFTER the exposure
88
If you were to image a finger using AEC, what would happen?
detector would see a lot of radiation
89
Using the two lateral detectors, do they see the same radiation or different?
50/50 (same)
90
What would happen if you were off center with AEC and soft tissue was an issue?
increased radiation exposure to IR = shorter exposure time than needed
91
What would happen if you were off center with AEC detector for chest and you centered over the spine?
Spine absorbs more radiation so higher mAs and longer exposure time
92
How will overexposure affect mAs?
will be higher than anticipated value
93
How will underexposure affect mAs?
will be lower than anticipated value
94
"fixed" image is the
raw data
95
Why 3 detectors with abdomen?
helps average out abdomen since there's a lot of organs, ST, air, gas
96
Issue with using AEC with barium?
detectors may be under barium (similar to metal)
97
Purpose of filters?
get rid of low E photons
98
Will AEC compensate for filtration?
yes, because it's before the AEC detector
99
Will AEC compensate for new IR having a different DQE?
No, because that doesn't occur before the IR
100
When anatomy is over less dense anatomy than needed, what happens to the image?
underexposure
101
When anatomy is over more dense anatomy than needed, what happens to the image?
overexposure
102
Purpose of falling load
to give us shorter exposure times
103
How do you shorten exposure with falling load?
go from 80% setting to 100% setting
104
If you're concerned with motion and you're using falling load with AEC, would you use 80% setting or 100% setting?
100% to get shorter time
105
what is the minimum response time
shortest exposure time possible with AEC
106
What causes changes in mAs (DI stays the same)
lateral decentering, increased SID, filtration, grid
107
What causes changes in mAs and DI
Improper centering, scatter, field size, wrong AEC detector, back up time, density selection
108
If you have to repeat an image after using AEC, what should you do?
use a fixed technique (UNLESS you know why - example: picked the wrong AEC detector)

MRT (12 decks)

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