PHYSICS - Mammo

Question 1

Ideal beam properties for mammography

Answer 1

low energy, nearly mono-energetic beam

Question 2

Typical kVp for mammo

Answer 2

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

Question 3

Dominant photon-tissue interaction in mammo

Answer 3

photoelectric effect (dominates at low energies)

Question 4

Typical SID for mammography

Answer 4

26” (or 65-70 cm)

Question 5

Spatial resolution for screen film mammo

Answer 5

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

Question 6

Spatial resolution for digital mammo

Answer 6

7 lp/mm

Question 7

Majority of x-rays in mammo are…

Answer 7

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

Question 8

Target/anode combinations for dense breasts

Answer 8

Rho/Rho or W/Ag

Question 9

X-ray spectrum in W/Ag setup

Answer 9

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

Question 10

K-shell binding energy of Moly

Answer 10

-20 keV

Question 11

K-shell binding energy of Rho

Answer 11

-23 keV

Question 12

K-shell binding energy of silver (Ag)

Answer 12

-25 keV

Question 13

Focal spot size (mammo)

Answer 13

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

Question 14

Mag view changes

Answer 14

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

Question 15

Effect of smaller focal spot

Answer 15

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

Question 16

mA for non-mag and mag views

Answer 16

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

Question 17

Heel effect

Answer 17

higher intensity beam on cathode side, and vice-versa

Question 18

Tube window material (mammography)

Answer 18

beryllium (vs. pyrex glass in general radiography)

Question 19

Standard compression force

Answer 19

25 lb (or 111 Newtons)

Question 20

Effect of compression on contrast

Answer 20

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

Question 21

Effect of compression on spatial resolution

Answer 21

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

Question 22

Grid ratio (mammo)

Answer 22

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

Question 23

Bucky factor (mammo)

Answer 23

2 (vs. 5 for general radiography)

Question 24

Scatter reduction in mammo is accomplished by…

Answer 24

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

Question 25

Mag view - spatial resolution factors

Answer 25

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)

Question 26

Mag view - patient dose factors

Answer 26

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

Question 27

Mag view - contrast factors

Answer 27

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

Question 28

Benefits of single emulsion film

Answer 28

less parallax, less crossover

Question 29

Drawback of single emulsion film

Answer 29

increased dose (relative to double emulsion)

Question 30

Film placed before screen to...

Answer 30

minimize halation (spread of light) which increases blurring

Question 31

Limiting factors for spatial resolution in film screen and digital mammo

Answer 31

focal spot size for film screen and pixel size for digital

Question 32

Artifact: residual image from prior exposure burned into detector

Answer 32

ghosting; seen with highly attenuating objects; "burned into detector"

Question 33

Air gap distance

Answer 33

15-30 cm

Question 34

"Contact mode"

Answer 34

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

Question 35

ACR breast phantom characteristics

Answer 35

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

Question 36

Mammo view naming convention

Answer 36

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

Question 37

Benefits of tomosynthesis

Answer 37

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

Question 38

Drawbacks of tomosynthesis

Answer 38

increased acquisition time => risk of motion artifact

Question 39

MQSA acronym + year + who created

Answer 39

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

Question 40

MQSA is enforced by...

Answer 40

the FDA, or separately by the VA for VA facilities

Question 41

MQSA regulates...

Answer 41

regulates dose, training, QC, and facilities

Question 42

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

Answer 42

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

Question 43

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

Answer 43

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

Question 44

Lay report due within...

Answer 44

30 days

Question 45

Referring physician report due within...

Answer 45

30 days

Question 46

PPV1 benchmark

Answer 46

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

Question 47

PPV2 benchmark

Answer 47

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

Question 48

PPV3 benchmark

Answer 48

cancers in patients who underwent biopsy; 31%

Question 49

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

Answer 49

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

Question 50

Mammo QC - digital machines

Answer 50

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

Question 51

MQSA requirement for spatial resolution

Answer 51

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

Question 52

Who sets and enforces mammo quality standards?

Answer 52

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