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Physics Chapter 13 > Ch 13 > Flashcards

Ch 13 Flashcards

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1
Q

System used to consistently control the amount of radiation reaching the image receptor by terminating the length of exposure

A

AEC

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2
Q

what determines the exposure time

A

AEC

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3
Q

When does AEC terminate

A

when’s predetermined amount of radiation has been detected

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4
Q

two types of AEC

A

pho timers and ionization chambers

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5
Q

refers to the use of an AEC device that uses photomultiplier tubes or photodiodes , and aren’t common today

A

photo timers

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6
Q

hollow cell that contains air and is connected to the timer circuit via electrical wires.

A

ionization chamber

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7
Q

why are ionization chamber aec devices considered to be entrance type devices ?

A

because they are positioned in front of the image receptor

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8
Q

AEC devices that measure the amount of radiation transmitted

A

detectors/ chambers/ cells

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9
Q

what used a fluorescent screen

A

photimers

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10
Q

what used a fluorescent screen and a device that converted the light to electricity

A

phototimers

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11
Q

electronic device that converts visible light energy into electrical energy

A

photomultiplier tube

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12
Q

where are phototimer aec devices placed

A

behind the image receptor

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13
Q

how do photimers work?

A

radiation reaches fluorescent light paddles producing visible light and PM tubes convert the light into electricity which trips the timer and exposure is terminated

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14
Q

how do ionization chamber aec work

A

radiation interacts either detectors and the air inside becomes ionized creating an electrical charge. the charge travels along the timer circuit and the timer is tripped, terminating exposure

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15
Q

which is less accurate
photo timers or ionization chambers

A

ionization chambers

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16
Q

what does AEC control

A

quantity of radiation reaching the image receptor

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17
Q

refers to the shortest exposure time that a system can produce

A

minimum response time

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18
Q

what is the minimum response time for modern AEC systems

A

1 ms

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19
Q

refers to the maximum amount of time the x ray exposure continues when using an AEC system

A

backup time

20
Q

acts as a safety mechanism when AEC fails

A

back up timer

21
Q

back up timer should be set at what percentage of the expected exposure time

A

150%-200%

22
Q

what are the density control button numbers?

A

-2, -1, 1, 2, and 3

23
Q

why shouldn’t toddlers be used for AEC

A

because they’re probably too small to even cover the detectors

24
Q

Refers to a radiographic system that allows the radiographer to select a particular button on the control panel that represents an anatomic area for which a preprogram set of exposure factors are displayed and can be selected

A

Anatomically program technique

25
Q

what’s an example of ANATOMIC programming

A

the difference in technique for an abdomen compared to a chest

26
Q

why is AEC calibration important

A

to ensure consistent and appropriate exposures to the receptor are being produced

27
Q

reproducibility for changes in exposure

A

5%

28
Q

reproducibility for pixel brightness levels

A

30%

29
Q

preestablish guidelines used by the radiographer to set standardized, manual, or AEC exposure factors for each type of radiographic examination

A

exposure technique chart

30
Q

Devices that measure part thickness

A

Calipers

31
Q

Based on the concept that KVP can be increased as the anatomic part size increases

A

variable kVp fixed mAs

32
Q

baseline kVp for variable kVp fixed mAs is increased by ___for every 1 cm increase in part thickness

A

2

33
Q

VARIABLE KVP FIXED MÁS
increase from 10 CM to 18 at 63 kVp
what would new kVp be

A

79
63+2 eight times

34
Q

VARIABLE MAS FIXED KVP
for every _________ cm change in thickness the mas should be adjusted by a factor of 2

A

4-5 cm

35
Q

is fixed kvp or variable kvp better

A

fixed kvp

36
Q

what happens when you do not collimate when using AEC

A

more scatter reaches AEC termination exposure early

37
Q

pediatric patient consideration

A

may not be able to cover detectors so manual technique with a shorter exposure time should be used

38
Q

geriatric patient considerations

A

may need decreased technique and short exposure time

39
Q

bariatric considerations

A

may need increase in technique, use of grid to control contrast

40
Q

does fiberglass require a change in technique

A

NO

41
Q

do plaster casts require an increase in technique

A

YES

42
Q

Diseases or conditions that decrease the absorption characteristics of the part, making that part less difficult to penetrate

A

Destructive diseases

43
Q

Diseases or conditions that increase the absorption characteristics of the part, making that part more difficult to penetrate

A

Additive diseases

44
Q

if the patient has an additive disease, what do we do with the KVP?

A

increase

45
Q

Examples of positive contrast agents

A

Barium and iodine

46
Q

Examples of negative contrast agent

A

air

47
Q

Do positive contrast agents produce more or less brightness

A

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Physics Chapter 13 (1 decks)

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