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AJT Physics > PHYSICS - Mammo > Flashcards

PHYSICS - Mammo Flashcards

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1
Q

Ideal beam properties for mammography

A

low energy, nearly mono-energetic beam

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2
Q

Typical kVp for mammo

A

25-30 kVp => average beam energy of 16-23 keV

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3
Q

Dominant photon-tissue interaction in mammo

A

photoelectric effect (dominates at low energies)

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4
Q

Typical SID for mammography

A

26” (or 65-70 cm)

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5
Q

Spatial resolution for screen film mammo

A

13 lp/mm in parallel direction and 11 lp/mm in the perpendicular direction; relative to anode-cathode axis

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6
Q

Spatial resolution for digital mammo

A

7 lp/mm

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7
Q

Majority of x-rays in mammo are…

A

characteristic x-rays (vs. Bremsstrahlung in general radiography)

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8
Q

Target/anode combinations for dense breasts

A

Rho/Rho or W/Ag

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9
Q

X-ray spectrum in W/Ag setup

A

composed of Bremsstrahlung (characteristic x-rays of W are removed by Ag filter)

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10
Q

K-shell binding energy of Moly

A

-20 keV

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11
Q

K-shell binding energy of Rho

A

-23 keV

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12
Q

K-shell binding energy of silver (Ag)

A

-25 keV

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13
Q

Focal spot size (mammo)

A

0.3 mm (non-mag views) and 0.1 mm (mag views)

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14
Q

Mag view changes

A

smaller focal spot, air gap, no grid, smaller compression paddle

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15
Q

Effect of smaller focal spot

A

higher resolution, more anode heating => lower mA => longer exposure required => higher chance of motion

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16
Q

mA for non-mag and mag views

A

100 mA and 50 mA, respectively; due to smaller focal spot for mag views

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17
Q

Heel effect

A

higher intensity beam on cathode side, and vice-versa

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18
Q

Tube window material (mammography)

A

beryllium (vs. pyrex glass in general radiography)

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19
Q

Standard compression force

A

25 lb (or 111 Newtons)

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20
Q

Effect of compression on contrast

A

reduced tissue thickness => less Compton scatter + more photons reach detector => kVp can be reduced => increased contrast

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21
Q

Effect of compression on spatial resolution

A

reduced tissue thickness => more photons reach detector => AEC reduces exposure time (lower mAs) => lower chance of motion => increased resolution

22
Q

Grid ratio (mammo)

A

5:1 (vs. 10:1 for general radiography)

23
Q

Bucky factor (mammo)

A

2 (vs. 5 for general radiography)

24
Q

Scatter reduction in mammo is accomplished by…

A

compression (thinner object), air gap, grid, lower kVp

25
Q

Mag view - spatial resolution factors

A

smaller focal spot increases resolution, but decreased SOD results in increased geometric blurring + longer exposure required due to heating increases chance of motion => net effect is INCREASED resolution (better)

26
Q

Mag view - patient dose factors

A

decreased SOD (air gap) => increased dose (by inverse square law), but grid removal results in decreased dose => net effect on dose is unclear

27
Q

Mag view - contrast factors

A

decreased scatter reaching detector (air gap) => increased contrast

28
Q

Benefits of single emulsion film

A

less parallax, less crossover

29
Q

Drawback of single emulsion film

A

increased dose (relative to double emulsion)

30
Q

Film placed before screen to…

A

minimize halation (spread of light) which increases blurring

31
Q

Limiting factors for spatial resolution in film screen and digital mammo

A

focal spot size for film screen and pixel size for digital

32
Q

Artifact: residual image from prior exposure burned into detector

A

ghosting; seen with highly attenuating objects; “burned into detector”

33
Q

Air gap distance

A

15-30 cm

34
Q

“Contact mode”

A

a.k.a. normal non-mag view; breast is in contract with grid/detector

35
Q

ACR breast phantom characteristics

A

4.2 cm thick, 50% glandular; contains 6 fibers, 5 masses, 5 specks

36
Q

Mammo view naming convention

A

based on path of penetration; e.g. ML view = source is medial, detector is lateral

37
Q

Benefits of tomosynthesis

A

improved contrast and specificity, decreased recall rate, increased cancer detection rate

38
Q

Drawbacks of tomosynthesis

A

increased acquisition time => risk of motion artifact

39
Q

MQSA acronym + year + who created

A

Mammography Quality and Standards Act (MQSA), 1992, created by congress

40
Q

MQSA is enforced by…

A

the FDA, or separately by the VA for VA facilities

41
Q

MQSA regulates…

A

regulates dose, training, QC, and facilities

42
Q

Average glandular dose for single image of breast phantom (with grid)

A

<3 mGy (applies to phantom, not actual patients); this is an MQSA regulation

43
Q

Average glandular dose for single image of breast phantom (no grid)

A

<1 mGy (applies to phantom, not actual patients); this is an MQSA regulation

44
Q

Lay report due within…

A

30 days

45
Q

Referring physician report due within…

A

30 days

46
Q

PPV1 benchmark

A

cancers in patients called back (BR-0, BR-3, BR-4, or BR-5); 4%

47
Q

PPV2 benchmark

A

cancers in patients recommended for biopsy (BR-4 or BR-5); 25%

48
Q

PPV3 benchmark

A

cancers in patients who underwent biopsy; 31%

49
Q

Effect of lower average beam energy (e.g. Mo/Mo) on AGD

A

lower beam energy => higher average glandular dose (lower energy x-rays do not penetrate)

50
Q

Mammo QC - digital machines

A

follow manufacturer’s recommendations (as opposed to all the dumb QC for screen film)

51
Q

MQSA requirement for spatial resolution

A

12 lp/mm for screen film, manufacturer resolution specifications for digital (usually 7 lp/mm)

52
Q

Who sets and enforces mammo quality standards?

A

FDA sets standards (MQSA); ACR enforces mammo quality standards

AJT Physics (7 decks)

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