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CORE Radiology Exam > Physics > Flashcards

Physics Flashcards

1
Q

“Joint Commission (JC) Sentinel Event is declared for unintended cumulative dose of

A

15 Gy to a single field (>1500 rads)

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2
Q

“Leakage radiation from the x-ray tube housing is limited to”

A

1 mGy/h at a distance of 1 meter

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3
Q

Max entrance air kerma (AK) rate in fluoro (non diagnostic) allowed by FDA is

A

100 mGy/min

No limit for DSA

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4
Q 
Fetal dose of > \_\_\_\_ 
are assoc. with
2w: fetal death
3-8w: congenital malformation
9-15w: growth or mental retardation
A

100 mGy

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5
Q

A ____ fetal absorbed dose during the first trimester can result in x3.5 inc risk of childhood CA

A

10 mGy

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6
Q

Dose rate limit of an unrestricted area

A

0.02 mSv in an hour

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7
Q

Annual radiation dose limit (total body of adult occupational worker in the US):

A

50 mSv

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8
Q

Avg risk of mortality from radiaton induced cancer in the gen pop

A

5% per Sv

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9
Q

Avg Abd/Pelvic CT exam dose

A

9 mSv

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10
Q

Natural background radiation in the United States

A

3 mSv/year

natural exposure: radon, solar etc.

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11
Q

Standard voltage for a CXR

A

120 kVp

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12
Q

Approximate power used to obtain an image with a plain film radiography

A

100 kW

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13
Q

Approximate power used to obtain a mammogram

A

3 kW or 30 kW? fix this

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14
Q

Appropriate entrance air kerma for an abdominal radiographs?

entrance skin dose?

A

3 mGy

~ 5mGy (usually about 50% more)

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15
Q

Pediatric protocol change for CT

A

Decrease kVP (eg from 120 - 80), decrease mA, decrease SFOV. Sometimes slight increase in mA to decrease shot noise.

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16
Q

Protocol change for CT in obese patients

A

Increase kVp to 140, and 120 for CTA

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17
Q

Protocol change for CT in angiography or CECT

A

Set kVp = 100 (Increases vessel and tissue contrast by choosing kVp so that kVavg is just above the Kedge of iodine (33keV) but even higher than DSAs 70 kVp to avoid grainy images.

18
Q

Standard phantom sizes for CT
head ___
abdomen____

A

16 cm

32 cm

19
Q

Effective dose equation

A

K x DLP

Where K accounts for tissue being scanned (brain vs breast)

20
Q

Absorbed dose (mGy): Definition?

A

Energy absorbed per mass in J/kg.

CTDIvol

21
Q

Equivalent dose (mSv):

A

Multiply the absorbed dose by the RADIATION weighing factor (Wr).
Allows to compare radiation types by cancer risk

22
Q

Radiation weighing factor for XRays

A

1

so, equivalent = absorbed

23
Q

Radiation weighing for alpha rays

A

20

24
Q

Radiation weighing for gamma rays

A

1 (Same as XR)

25
Q

Effective dose

A

Multiply absorbed dose by TISSUE weighing factor. Accounts for tissue type irradiated (more radiosensitive tissues have larger Wt)

26
Q

1 Rem = ____ mSV

A

10

27
Q

Gamma should be shielded using

A

High Z material such as lead. Concrete can be used as building material.

28
Q

Termination should only be considered for fetal absorbed dose of ____ between the ____ weeks of gestation

A

> 50 mGy, 2-15

29
Q

Avg person in the US is exposed to approximately ____ mSv annually

A

6.2

~half from natural, half from medical

30
Q

Rad units operated above > 70kVp should contain a filtration of at least how much of aluminum equivalent

A

2.5mm

31
Q

Fetal absorbed doses of more than ____ occurring during ____ of gestation may result in fetal death.

A

25mGy, 3-8w

32
Q

The lethal dose in 50% of humans in 60 days is referred to as LD50/60 and occurs at what level of radiation?

A

3.5-7 Gy. Depends on level of medical care following exposure.

33
Q

What radiation induced cancer has the shortest latency period?

A

Leukemia (5-15yrs)

vs solid tumors 20-60yrs

34
Q

No deterministic effects from radiation have been proven below which does level?

A

0.1 Gy

35
Q

Improve streak artifact by

A

increasing kVp

36
Q

DLP equation

A

CTDIvol x scan length

37
Q

CTDIvol is estimated using

A

an acrylic phantom.

Overestimated in obese pts and underestimates in peds.

38
Q

Of the four basic dose units ________ is the closest measure of cancer risk; it accounts for both radiation type and tissue type.

A

effective dose

39
Q

Kerma-Area Product (KAP) equation

A

“KAP = AK x (Area Exposed)” measured in Gy-cm2

40
Q

KAP relates to _____ risk while AK relates to ______ risk.

A

stochastic (cancer); deterministic

CORE Radiology Exam (16 decks)

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