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XR Physics > 5. Mammo > Flashcards

5. Mammo Flashcards

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1
Q

difference in mammo XR

A
  • lower energy monoenergetic beam to enhance attenuation differences
  • increase in spatial resolution to see microcalculations
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2
Q

mammo – optimal kVp

A

ideal kVp: 16-23 keV ; voltage of 25-30 kVp is used (Dx is usually 50-120)

-PE dominates at low kvP; PE proportional to Z^3 and indirectly with energy 1/E^3

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3
Q

mammo – target, characteristic x-rays

A

mammo uses molybednum or rhodium anode

moly: 18 keV ; rhodium: 20.2 keV

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4
Q

why is moly used for mammo

A

low atomic number, generate low K characteristic x-rays

peak characteristic x-rays with low Bremsstrahlung

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5
Q

k-edge filtration

A

filter placed outside of tube to create mono-energetic beam (<15 keV and >20 filtered out)

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6
Q

when is Rh vs Mo used?

A

Rh used for denser breasts since it’s higher energy

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7
Q

why would Mo anode and Rh filter be used?

A

intermediate energy spectrum

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8
Q

would you ever use Rh target (21 kev) and Mo filter (20 kev K edge)?

A

NO

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9
Q

when is Mo anode used with aluminium filter?

A

harder beam to penetrate denser breasts

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10
Q

increasing the filter k edge will result in beam ? and contrast ?

A

increases average energy of beams

reduces contrast

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11
Q

mammo – focal spot size

A

0.1-3 small; better spatial resolution

general x ray 0.6-1.2 mm

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12
Q

problems with small focal spot size

A

cannot tolerate heat well, must have lower mA (and requires longer exposure time)

mA 50 for 0.1 mm focal size
mA 100 for 0.3 mm focal size

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13
Q

mammo – exposure time

A

longer than xray

mammo ~1 sec
abdominal x ray 0.05 sec
CXR 0.005 sec

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14
Q

heel effect and mammography; which side does cathode go on?

A

cathode goes on chest wall

tube angled up 20 degrees

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15
Q

effective anode angle

A

effective anode angle = anode + tube tilt angle

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16
Q

diagnostic tube for mammo vs xr?

A

mammo: beryllium exit window (less attenuation)

Dx: glass

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17
Q

reason for breast compression in mammo?

A

reduced thickness/scatter so lower kVP can be used
lower kVP/scatter so improved contrast
improved tissue penetration, so less dose/scatter
reduced thickness so less mAs/dose needed
no motion so less motion/focal blur and spatial resolution
less geometric magnification
less tissue overlap

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18
Q

antiscatter grid in mammo

A

4-5 grid ratio (height/width)

smaller grid ratio and lower kVp (reduces scatter)

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19
Q

problems with grid

A

increased dose with grid since grid removes scatter

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20
Q

bucky factor for mammo vs XR

A

mammo: 2
XR: 5

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21
Q

mag view of breast?

A

move breast away from detector and closer to the source/focal spot

cutting distance to source in half doubles the mag

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22
Q

is there a grid in mag view?

A

no. instead the air gap is used as a grid

the air gap allows off axis scatter to miss the target

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23
Q

major changes with mammography and XR

A 
smaller focal spot
less mA (to not melt focal spot)
longer exposure time to compensate for increase distance between breast tissue and image receptor
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24
Q

difference between mammo and mag view

A

no grid, even smaller focal spott, increase exposure time, less mA

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25
Q

optical density in mammo

A

high maximum optical density, most useful at periphery of breast (skin) where thickness decreases

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26
Q

air kerma? relationship with distance

A

density of xrays ; decreases via inverse square law with distance

27
Q

entrance air kerma

A

radiation incident on patient

28
Q

receptor air kerma

A

radiation used to generate image

29
Q

which is bigger, entrance vs receptor air kerma?

A

receptor AK less than entrance

30
Q

air kerma in mammo

A

higher than in general XR

usually because source to image distance is much smaller in mamms compared to DX

31
Q

digital mammo vs analog with spatial resolution?

A

digital systems have lower spatial resolution

32
Q

is there a specific line pair requirement MQSA for digital?

A

no; manufacturers specifications

33
Q

digital mammography dose?

A

less than analog ~15% because of better beam quality

34
Q

digital mammography noise?

A

fixed after exposure is taken

dark noise: electronic fluctuations within detector element; proportional to temperature of detector

35
Q

flat field test

A

imaging acrylic to improve image quality and calibrate digital detectors

36
Q

ghosting in mammo

A

residual image from prior exposure tpically from high attenuating objects (like lead) placed in beam

reasons lead is not allowed on flat panel digital systems

37
Q

pixels gone bad

A

square or streak

38
Q

digital artifacts in mammo

A

ghosting, pixels gone bad

39
Q

digital breast tomosynthesis

A

stacked images taken in 15 prjections that decreases the effects of tissue superimposition

improves sensitivity/specificity

40
Q

pros/cons of DBT

A

pros: better margins/shapes
cons: density of a mass may appear decreased ; intralesional fat may be benign but should prompt biopsy as cancers may loo like they are engulfing fat

mildly increased dose

41
Q

PPV

A

positive predictive value

proportion of people with a postive study who have breast cancer

positive exam / (all positive exams–cancer and overcalls)

42
Q

benchmark for PPV1

A

positive screening – BR 0, 3-5 or call backs

benchmark -4.4.%

43
Q

benchmark for PPV2

A

callbacks where biopsy recommended – BR 4-5

benchmark - 25.4%

44
Q

benchmark for PPV3

A

results of biopsy; positive biopsy rate , biopsy yield of malignancy

benchmark: 31%

45
Q

how often is mammo accredited/certified?

A

3 years

46
Q

who monitors MQSA

A

FDA

47
Q

who is responsible for QA and QC per MQSA?

A

interpreting physician

48
Q

minimum megapixels on a mammo workstation

A

3 MP

49
Q

target range for medical audit: recall rate

A

5-7%

50
Q

target range for medical audit: cancers/1000 screened

A

3-8

51
Q

processor QC frequency

A

daily

52
Q

darkroom cleanliness frequency

A

daily

53
Q

viewbox conditions frequency

A

weekly

54
Q

phantom evaluation frequency

A

weekly

55
Q

repeat analysis frequency

A

quarterly

56
Q

compression test frequency

A

semi-annually

57
Q

darkroom fog frequency

A

semi-annually

58
Q

screen-film contrast frequency

A

semi-annually

59
Q

mammo requirements

A

240 mammograms in the last 2 years of training (during a 6 month period)

3 months of formal training

60 documented hours of mammo education

60
Q

how many line pairs/mm for the anode-cathode direction and in the left right direction?

A

anode-cathode: 13 LP/min

left-right: 11 LP/min

61
Q

MQSA requirmeents for screen film and manufacture spects for digital?

A

12 lp/mm for screen-film

manufacture specs for digital ~7 lp/mm

62
Q

breast phantom specs

A

4.2 cm of breast tissue is 50% adipose/glandular

63
Q

average compressed breast thickness/glandularity in the US

A

60 mm, ~15% glandularity

64
Q

phantom mammo limit

A

3 mGy with grid

1 mGy w/o a grid

XR Physics (6 decks)

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