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Radiology CORE Exam > Physics > Flashcards

Physics Flashcards

1
Q

Tungsten K shell binding energy

A

-69.5 keV

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2
Q

Molybdenum K shell binding energy

A

-20 keV

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3
Q

How does intensity relate to kVp?

A

Directly proportional to kVp squared

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4
Q

Increasing kVp does what to quality and quantitiy?

A

Increase both

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5
Q

Increasing mAs does what to quality and quantity?

A

Increases quantity only, no effect on quality

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6
Q

What is quality of the beam?

A

Overall energy of the beam, or, ability to penetrate an object

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7
Q

What is the effect of increasing Z on Q/Q?

A

Different characteristic peaks but no change in quality, overall quantity increases due to more Brems

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8
Q

Decreasing voltage ripple results in (Q/Q)?

A

Increasing average energy and more overall xrays bc more Brems

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9
Q

How does mAs affect quantity?

A

Directly proportional

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10
Q

How does distance affect quantity?

A

Decreases with inverse square

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11
Q

How does kVp affect quantity?

A

Approximately square increase

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12
Q

How does increasing filtration affect Q/Q?

A

Improved quality, decreased quantity

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13
Q

What increase in photons (mAs) will cut mottle by half?

A

4x increase

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14
Q

mAs is the most important factor for?

A

noise (mottle)

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15
Q

If you increase mAs from 50 to 200, what happens to noise?

A

Decrease by 50%

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16
Q

Magnification factor (MF) =

A

Source to Detector Distance / Source to Patient Distance

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17
Q

How does detective quantum efficiency related to dose?

A

Inverse, a high DQE= low dose

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18
Q

What is the relationship between incident photon energy and probability of photoelectric effect?

A

1/E^3

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19
Q

What is the relationship between tissue Z and probability of photoelectric effect?

A

Directly proportional to Z^3, means small differences in tissue (mammo) as long as incident photon energy is low, will still give contrast difference

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20
Q

How often are mammo facilities accredited?

A

Every 3 years

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21
Q

Who regulates MQSA?

A

FDA (Mammography Quality Standards Act)

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22
Q

Who is responsible for mammo QA/QC?

A

The interpreting physician

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23
Q

Minimum meagpixels for a mammo workstation?

A

3mp

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24
Q

What is the target recall rate for mammo?

A

5-7%

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25
Q

What is the target cancer rate for mammo?

A

3-8/1000 screened

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26
Q

How often is mammo processor QC performed?

A

Daily

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27
Q

How often is mammo darkroom cleanliness ensured?

A

Daily

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28
Q

How often are mammo viewbox conditions inspected?

A

Weekly

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29
Q

How often is mammo phantom evaluation performed?

A

Weekly

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30
Q

How often is mammo repeat analysis performed?

A

Quarterly

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31
Q

How often is mammo compression test performed?

A

Semi-annually

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32
Q

How often is mammo darkroom fog tested?

A

Semi-annually

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33
Q

How often is mammo screen-film contrast checked?

A

Semi-annually

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34
Q

What is required for residents to be signed off to read mammo?

A

240 exams within 6 month period in last two years, 3 months formal training, 60 hours education

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35
Q

What are the characteristics of the breast phantom?

A

4.2cm compressed, 50% fat/50% glandular

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36
Q

What is the maximum dose allowed for the breast phantom (with and without grid)?

A

300 millirads (mGy) WITH a grid, 1 mGy without

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37
Q

What is the benchmark and acceptable rate for abnormal screeners (call backs AKA PPV1)?

A

4.4%

3-8%

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38
Q

What is the benchmark and acceptable rate for biopsy recommended (BR 4/5 AKA PPV2)?

A

25.4%
15-40%
25-50% if palpable

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39
Q

What is the benchmark and acceptable rate for positive results on biopsy (AKA PPV3)?

A

31%
20-45%
30-55% if palpable

40
Q

What target/filter combo is best for large/dense breasts?

A

Rh/Rh or Mo/Al

41
Q

What target/filter combo is best for intermediate size/density breasts?

A

Mo/Rh

42
Q

What target/filter combo is best for small/thin size/density breasts?

A

Mo/Mo

43
Q

What combo of target/filter in mammo is never used?

A

Rh/Mo because Rh has 21 kev and Mo filter has 20 k edge, so all characteristic x rays would be absorbed by filter

44
Q

What is the max exposure rate of an II system?

A

87mGy/min or 10 R/min

45
Q

What does electronic mag do to air kerma?

A

Increases, more energy in a smaller area

46
Q

What does electronic mag do to kerma (dose) area product?

A

No change, because smaller area cancels it out

47
Q

How does collimation affect kerma (dose) area product?

A

Decreased, collimation usually is not accompanied by an increase in beam dose

48
Q

Where is optimal patient positioning on a fluoro unit?

A

Source below table, patient as close to detector as possible

49
Q

For large patients, what is the high level control limit of fluoroscopy?

A

176 mGy/min or 20 R/min

50
Q

If binning is utilized, what happens to SNR?

A

It improves

51
Q

How does decreased field of view affect spacial resolution in fluoro?

A

It improves

52
Q

What is the operator dose in fluoro outside lead relative to patient dose?

A

1/1000th patient dose

53
Q

Acute radiation syndrome: bone marrow dose and outcome

A

> 2Gy, often survive

54
Q

Acute radiation syndrome: Gi dose and outcome

A

> 8Gy, dead in 2 weeks

55
Q

Acute radiation syndrome: CNS dose and outcome

A

> 20-50Gy, death in 3 days

56
Q

What is the fluoro dose cutoff for transient erythema?

A

2 Gy (occurs within 24 hours)

57
Q

What is the fluoro dose cutoff for main erythema?

A

6 Gy (around 2 weeks) (RP says 5 Gy)

58
Q

What is the fluoro dose cutoff for temporary epilation (hair loss)?

A

3 Gy (around 3 weeks)

59
Q

What is the fluoro dose cutoff for permanent epilation (hair loss)?

A

7 Gy (around 3 weeks)

60
Q

What is the fluoro dose cutoff for dry desquamation?

A

14 Gy (usually around 4 weeks)

61
Q

What is the fluoro dose cutoff for moist desquamation?

A

18 Gy (usually around 4 weeks)

62
Q

What is the fluoro dose cutoff for secondary ulceration?

A

24 Gy (greater than 6 weeks post)

63
Q

What is the fluoro dose cutoff for dermal atrophy?

A

10 Gy (~1 year later)

64
Q

What is the fluoro dose cutoff for telangiectasis?

A

10 Gy (~ 1 year later)

65
Q

What is the fluoro dose cutoff for dermal necrosis?

A

> 12 Gy (~1 year later)

66
Q 
What values trigger clinical follow up for skin reactions?
Peak Skin Dose
Cumulative Air Kerma
Kerma Air Product
Fluoro Time
A

> 2 Gy
5 Gy
500 Gy cm^2
60 mins

67
Q

What risk factors are most important for radiation burns?

A

Obesity, previous radiation exposure

68
Q

US regulatory dose limit for a radiologist in 1 year

A

50 mSv (typical dose is 5 mSv)

69
Q

US regulatory dose limit to eye

A

150 mSv/year

70
Q

ICRP Dose limit to eye

A

20 mSv/year

71
Q

Minimum allowed lead apron thickness

A

0.25mm

72
Q

Cutoff for sentinel event in fluoro

A

> 1500 Rads (15 Gy) to a single field

Requires root cause analysis w/in 45 days and medical monitoring for skin burn

73
Q

Acute exposure threshold for cataracts

A

0.5Gy per RP

74
Q

Threshold for male sterility
Temporary
Permanent

A

0.15-2.5Gy - per RadPrimer 0.1 is the new lower limit and 2.5Gy is an old value
5Gy (RP says 6Gy)

75
Q

Female permanent sterility
Age 12
Age 45
Age not given

A

10 Gy
2 Gy
6 Gy
RP says 3 Gy

76
Q

Whole body dose to cause nausea

A

0.75-1.25Gy

RP says whole body dose for majority of population to exhibit symptoms of acute radiation illness is 1Gy

77
Q

Whole body dose to suppress circulating WBCs

A

0.25 Gy

78
Q

LD 50/60 (marrow)

A

3-4Gy

79
Q

LD 50/4 (GI)

A

8-10 Gy

80
Q

LD for CNS

A

> 20Gy

81
Q

Double the natural or spontaneous mutation rate

A

1Gy

82
Q

Effective dose from background radiation in US each year

A

3mSv

83
Q

Occupational exposure limit for an extremity per year

A

500 mSv

84
Q

Mammo room door thickness equal to

A

1mm Steel, also double layers of 5/8 drywall

85
Q

The majority of energy received by biologic material from x rays is transferred by

A

electrons

86
Q

Approximately 60% of damage to biologic material from x rays is mediated by

A

free radicals

87
Q

Risk of radiation induced cancer

A

4-5% per Sv for adults
15% per Sv for children
Per RP (new BEIR report) - 8% per Gy/Sv males, 13% females

88
Q

Carcinogenesis by radiation is

A

stochastic (all or nothing)

89
Q

What dose constitutes a sentinel event?

A

15 Gy

90
Q

What is the single largest contributor to yearly dose to the public in the US?

A

Inhaled radon

91
Q

What is the largest contributor to yearly dose as a result of human activity?

A

Medical imaging

92
Q

Max fringe field outside controlled MR area

A

5 Gauss

93
Q

What is the SAR limit for whole body

A

4 W/Kg for 15 min

94
Q

What is the SAR limit for the head

A

3 W/kg over 10 min

95
Q

Written instructions are required to release a patient treated with a radiopharmaceutical (like I131) if there is potential for other persons to be exposed to what dose?

A

1mSv (0.1 rem)

Radiology CORE Exam (3 decks)

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