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Radiology CORE Exam > Physics > Flashcards

Physics Flashcards

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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
What is the target cancer rate for mammo?
3-8/1000 screened
26
How often is mammo processor QC performed?
Daily
27
How often is mammo darkroom cleanliness ensured?
Daily
28
How often are mammo viewbox conditions inspected?
Weekly
29
How often is mammo phantom evaluation performed?
Weekly
30
How often is mammo repeat analysis performed?
Quarterly
31
How often is mammo compression test performed?
Semi-annually
32
How often is mammo darkroom fog tested?
Semi-annually
33
How often is mammo screen-film contrast checked?
Semi-annually
34
What is required for residents to be signed off to read mammo?
240 exams within 6 month period in last two years, 3 months formal training, 60 hours education
35
What are the characteristics of the breast phantom?
4.2cm compressed, 50% fat/50% glandular
36
What is the maximum dose allowed for the breast phantom (with and without grid)?
300 millirads (mGy) WITH a grid, 1 mGy without
37
What is the benchmark and acceptable rate for abnormal screeners (call backs AKA PPV1)?
4.4% | 3-8%
38
What is the benchmark and acceptable rate for biopsy recommended (BR 4/5 AKA PPV2)?
25.4% 15-40% 25-50% if palpable
39
What is the benchmark and acceptable rate for positive results on biopsy (AKA PPV3)?
31% 20-45% 30-55% if palpable
40
What target/filter combo is best for large/dense breasts?
Rh/Rh or Mo/Al
41
What target/filter combo is best for intermediate size/density breasts?
Mo/Rh
42
What target/filter combo is best for small/thin size/density breasts?
Mo/Mo
43
What combo of target/filter in mammo is never used?
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
What is the max exposure rate of an II system?
87mGy/min or 10 R/min
45
What does electronic mag do to air kerma?
Increases, more energy in a smaller area
46
What does electronic mag do to kerma (dose) area product?
No change, because smaller area cancels it out
47
How does collimation affect kerma (dose) area product?
Decreased, collimation usually is not accompanied by an increase in beam dose
48
Where is optimal patient positioning on a fluoro unit?
Source below table, patient as close to detector as possible
49
For large patients, what is the high level control limit of fluoroscopy?
176 mGy/min or 20 R/min
50
If binning is utilized, what happens to SNR?
It improves
51
How does decreased field of view affect spacial resolution in fluoro?
It improves
52
What is the operator dose in fluoro outside lead relative to patient dose?
1/1000th patient dose
53
Acute radiation syndrome: bone marrow dose and outcome
>2Gy, often survive
54
Acute radiation syndrome: Gi dose and outcome
>8Gy, dead in 2 weeks
55
Acute radiation syndrome: CNS dose and outcome
>20-50Gy, death in 3 days
56
What is the fluoro dose cutoff for transient erythema?
2 Gy (occurs within 24 hours)
57
What is the fluoro dose cutoff for main erythema?
6 Gy (around 2 weeks) (RP says 5 Gy)
58
What is the fluoro dose cutoff for temporary epilation (hair loss)?
3 Gy (around 3 weeks)
59
What is the fluoro dose cutoff for permanent epilation (hair loss)?
7 Gy (around 3 weeks)
60
What is the fluoro dose cutoff for dry desquamation?
14 Gy (usually around 4 weeks)
61
What is the fluoro dose cutoff for moist desquamation?
18 Gy (usually around 4 weeks)
62
What is the fluoro dose cutoff for secondary ulceration?
24 Gy (greater than 6 weeks post)
63
What is the fluoro dose cutoff for dermal atrophy?
10 Gy (~1 year later)
64
What is the fluoro dose cutoff for telangiectasis?
10 Gy (~ 1 year later)
65
What is the fluoro dose cutoff for dermal necrosis?
>12 Gy (~1 year later)
66
``` What values trigger clinical follow up for skin reactions? Peak Skin Dose Cumulative Air Kerma Kerma Air Product Fluoro Time ```
>2 Gy 5 Gy 500 Gy cm^2 60 mins
67
What risk factors are most important for radiation burns?
Obesity, previous radiation exposure
68
US regulatory dose limit for a radiologist in 1 year
50 mSv (typical dose is 5 mSv)
69
US regulatory dose limit to eye
150 mSv/year
70
ICRP Dose limit to eye
20 mSv/year
71
Minimum allowed lead apron thickness
0.25mm
72
Cutoff for sentinel event in fluoro
>1500 Rads (15 Gy) to a single field | Requires root cause analysis w/in 45 days and medical monitoring for skin burn
73
Acute exposure threshold for cataracts
0.5Gy per RP
74
Threshold for male sterility Temporary Permanent
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
Female permanent sterility Age 12 Age 45 Age not given
10 Gy 2 Gy 6 Gy RP says 3 Gy
76
Whole body dose to cause nausea
0.75-1.25Gy | RP says whole body dose for majority of population to exhibit symptoms of acute radiation illness is 1Gy
77
Whole body dose to suppress circulating WBCs
0.25 Gy
78
LD 50/60 (marrow)
3-4Gy
79
LD 50/4 (GI)
8-10 Gy
80
LD for CNS
>20Gy
81
Double the natural or spontaneous mutation rate
1Gy
82
Effective dose from background radiation in US each year
3mSv
83
Occupational exposure limit for an extremity per year
500 mSv
84
Mammo room door thickness equal to
1mm Steel, also double layers of 5/8 drywall
85
The majority of energy received by biologic material from x rays is transferred by
electrons
86
Approximately 60% of damage to biologic material from x rays is mediated by
free radicals
87
Risk of radiation induced cancer
4-5% per Sv for adults 15% per Sv for children Per RP (new BEIR report) - 8% per Gy/Sv males, 13% females
88
Carcinogenesis by radiation is
stochastic (all or nothing)
89
What dose constitutes a sentinel event?
15 Gy
90
What is the single largest contributor to yearly dose to the public in the US?
Inhaled radon
91
What is the largest contributor to yearly dose as a result of human activity?
Medical imaging
92
Max fringe field outside controlled MR area
5 Gauss
93
What is the SAR limit for whole body
4 W/Kg for 15 min
94
What is the SAR limit for the head
3 W/kg over 10 min
95
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?
1mSv (0.1 rem)

Radiology CORE Exam (3 decks)

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