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Physics - Common Equipment > Chapter 13 > Flashcards

Chapter 13 Flashcards

1
Q

How do AEC detectors function?

A

Radiation is transmitted through the patient and converted into an electrical signal that terminates the exposure

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2
Q

A system that controls the duration of the exposure and the amount of radiation used

A

AEC

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3
Q

2 types of AEC systems

A

Phototimers
Ionization chambers

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4
Q

Phototimers used a fluorescent screen coupled with a:

A

Photomultiplier tube or a photodiode

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5
Q

What is the function of photomultiplier tubes and photodiodes?

A

Covert light into electric signal

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6
Q

Phototimer AECs are _____ devices

A

Exit-type

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7
Q

What is an exit-type device?

A

Radiation has to pass through the IR before it can be measured and used to terminate the exposure

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8
Q

Currently, most AEC devices use this type of detector:

A

Ionization chambers

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9
Q

What is an ionization chamber?

A

Hollow cell filled with air, connected to a timer circuit via electrical wire

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10
Q

Ion chamber devices are _______ devices:

A

Enterance-type

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11
Q

What are enterance-type devices?

A

Positioned in front of the IR

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12
Q

What do ion chambers measure?

A

DAP

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13
Q

How do ion chambers function?

A

Once the correct amount of DAP has been detected, an electric signal is sent from the chambers that is used to terminate the exposure

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14
Q

Why are ionization chambers the most common form of AEC?

A

Less sophisticated and accurate than phototimers but much less prone for failure

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15
Q

AEC controls only the _____ of radiation that reaches the IR

A

Quantity

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16
Q

Does AEC affect contrast?

A

No

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17
Q

Using higher kVp with AEC will result in a _______ exposure time

A

Shorter

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18
Q

Lower mA will result in a _____ exposure time

A

Longer

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19
Q

Minimum response time is the ________ exposure time a system can produce

A

Shortest

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20
Q

Minimum response time is usually _______ with AEC systems

A

Longer

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21
Q

Backup time is the ______ length of time an exposure can go when using AEC

A

Maximum

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22
Q

The backup timer should be set to terminate the exposure at ____%

A

150-200

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23
Q

Exposure adjustment is also known as

A

Density controls

24
Q

What is the function of density controls?

A

Increase or decrease the preset exposure levels by a preset amount

25
Q

What AEC cells should be selected?

A

That cells that will collect radiation that has passed through the patient first

26
Q

Is detector size and placement in an AEC system fixed or unfixed?

A

Fixed

27
Q

AEC is designed to compensate for changes in:

A

Patient thickness

28
Q

Destructive pathologies can cause ____ of the area of interest

A

Underexposure

29
Q

Additive pathologies can cause _____ of the area of interest

A

Overexposure

30
Q

True/False - the size of the field can also affect AEC exposure

A

True

31
Q

Wide open collimation is going to result in _____ scatter

A

More

32
Q

More scatter allows the AEC cells to be irradiated quicker than intended, resulting in an _________ image

A

Underexposed

33
Q

Collimation that is too tight may result in an ________ image

A

Overexposed

34
Q

Exposures need to be able to reproduce using the same technical factors that provide mR reading within __% of each other, and with pixel brightness levels within ____% of each other

A

5%
30%

35
Q

Exposure technique charts are based on:

A

Part thickness

36
Q

Two primary types of exposure technique charts

A

Variable kVp/fixed mAs
Fixed kVp/Variable mAs

37
Q

What are variable kVp charts based on?

A

kVp can be increased as part thickness is increased

38
Q

How is kVp adjusted as part thickness increases

A

kVp is increased by 2 for every 1cm increase in part thickness

39
Q

Why is variable kVp not ideal?

A

Because kVp changing kVp impacts contrast

40
Q

How is mAs adjusted as part thickness increases

A

For every 4-5cm increase in part thickness, mAs is adjusted by a factor of 2

41
Q

What types of casts require increased exposure factors?

A

Plaster

42
Q

When do splints require an increase in technique

A

When the splint overlies the anatomy of interest

43
Q

If the disease is an additive pathology, you may need to _________ factors

A

increase

44
Q

If the disease is a destructive pathology, you may need to __________ factors

A

Decrease

45
Q

Should mAs or kVp be adjusted for additive/destructive diseases?

A

kVp

46
Q

Positive contrast media shows up ________ than the surrounding tissue

A

Lighter

47
Q

Negative contrast media shows up ___________ than the surrounding tissue

A

Darker

48
Q

What exposure factors should be adjust when using positive contrast?

A

kVp

49
Q

Additive conditons in the abdomen

A

Aortic aneurysm
Ascities
Cirrhosis
Hypertrophy

50
Q

Additive conditions in the chest

A

Atelectasis
Congestive heart failure
Malignancy
Pleural effusion
Pnemonia

51
Q

Additive conditions in the skeleton

A

Hydrocephalus
Metastases (osteoblastic)
Osteochondroma
Paget disease

52
Q

Additive conditions in nonspecific sites

A

Abscess
Edema
Sclerosis

53
Q

Destructive conditions in the abdomen

A

Bowel obstruction
Free air

54
Q

Destructive conditions in the chest

A

Emphysema
Pneumothorax

55
Q

Destructive conditions in the skeleton

A

Gout
Metastases (osteolytic)
Multiple myeloma
Paget disease

56
Q

Destructive conditions in nonspecific sites

A

Atrophy
Emaciation
Malnutrition

Physics - Common Equipment (7 decks)

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