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Huda > Chapter 8 Mammography > Flashcards

Chapter 8 Mammography Flashcards

1
Q

cancer detection rates with mammo

A

-4/1000

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2
Q

mammo views of the breast

A

craniocaudal
medio-lateral oblique

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3
Q

size and glandularity for average compressed breast

A

60 mm thick
15 % glandularity

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4
Q

what are microcalcifications

A

specks of calcium hydroxyapatite that have high attenuation coefficients

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5
Q

why is detection and characterization of microcalcification hard?

A

small dimension (0.1 mm diameter)

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6
Q

spatial resolution in mammo compared to human eye

A

superior to human eye at 25 cm viewing distance

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7
Q

how is mammo contrast increased?

A

using low-energy photons

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8
Q

how is noise reduced?

A

high radiation intensities at image receptor

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9
Q

digital mammo contrast, noise, and resolution vs other x-ray medical x-ray imaging modality?

A

mammo is superior

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10
Q

density of calcification vs adipose
fibroglandular vs carcinoma

A

2.2 g/cm3 vs 0.93 g/cm3 adipose tissue
1.04 g/cm3 fibroglandular vs 1.05 g/cm3 carcinoma

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11
Q

most common target material

A

molybdenum (Z= 42)
tungsten (Z= 74) is becoming more common, with no characteristic x-ray and more bremstrahlung

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12
Q

focal spot size

A

0.3 mm
small focal spot 0.1 mm for magnification mammo

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13
Q

why is a berrylium x-ray tube window used?

A

Z=4
minimizes x-ray beam attenuation

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14
Q

how is heel effect used?

A

used to increase radiation intensity at chest wall by pointing anode towards nipple

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15
Q

how is spectral shape obtained?

A

using K-edge filters (Mo, Rh, Ag)

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16
Q

tube voltages in mammo

A

25-35 kV
-avg x-ray beam energy is governed with the K edge filters

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17
Q

tube currents

A

100 mA in contact mammography
25 mA in magnification mammo

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18
Q

exposure times

A

1 s

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19
Q

power loading in mammo

A

3 kW in contact mammo
<1 kW in magnification mammo

vs CT 100 kW

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20
Q

what do the filters do?

A

remove low energy x-rays that only contribute to dose

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21
Q

Mo/Mo target/filter

A

Mo K edge is 20 keV
-filter attenuates photons above K edge

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22
Q

Mo/Rh target/filter

A

Rh K edge is 23 keV
-allows x-rays up to 23 keV (higher average energy than Mo/Mo)

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23
Q

characteristic Mo x-ray energies

A

19.6 keV and 17.5 keV

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24
Q

filters used with tungsten targets

A

Rh or Ag
Ag K-edge is 25 keV

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25
Q

what photons do the filters remove?

A

low energy photons and those above their k-edge

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26
Q

average energy and HVL of a W/Ag combination vs W/Rh combination

A

W/Ag is higher
With W targets, the average energy of transmitted photons is always “slightly less than” the K-edge energy of the K-edge filter

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27
Q

beam qualities of W targets vs Mo targets

A

W is higher

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28
Q

for what breast thickness do we use the different target/filter combinations and what is respective HVL?

A

Mo/Mo, < 65 MM, hvl 0.35 MM aL
Mo/Rh, > 65 mm, HVL 0.45 mm Al
W/Rh, < 65 mm, HVL 0.5 mm Al
W/Ag, > 65 mm, HVL 0.6 mm Al

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29
Q

scatter to primary ratio

A

1:1

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30
Q

does PE or compton dominate?

A

PE, opposite of other radiography

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31
Q

source to image distance

A

65 cm (shorter than 100 cm in other radiography)

longer SIDs would be unacceptable exposure times; shorter SIDs would increase focal spot blur and distortion

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32
Q

why use breast compression?

A

-immobilizes breast, minimizing motion blur
-spreads out breast tissue to decrease tissue overlap
-compression brings breast closer to imaging plane, minimizing image magnification and reducing focal spot blur
-compression results in increased penetration, which reduces exposure times and radiation doses

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33
Q

compression force

A

25-45 lb

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34
Q

grids in mammo

A

grid ratio 5:1
grid line densities of 50 lines/cm
other radiographic imaging often uses 10:1 grid

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35
Q

what does HTC grid do?

A

-high transmission cellular grid
-honeycomb pattern
-improve scatter removal because of 2D structure
-improve primary transmission because interspace material is air with negligible transmission

36
Q

bucky factor of mammo grids

A

2
doubles dose
benefit of contrast outweighs risk of dose

37
Q

other than grid, what else can mammo use?

A

air gap in magnification mammo
reduces mAs because primary photon losses don’t occur due to a grid

38
Q

what does digital mammo use?

A

scintillators (CsI) or photoconductors (Se)

39
Q

CsI vs Se pros and cons

A

both absorb >90% of mammo photons
CsI= faster and more reliable
Se = better resolution

40
Q

use of photostimulable phosphors?

A

have been used, but have worse resolution and inferior clinical detection

41
Q

are scintillators phosphors?

A

all scintillators can be phosphor but not all phosphors are scintillators

-phosphor shows luminescence after being stimulated
-scintillators show luminscence after being stimulated with ionizing radiaiton specifically. Also scinntillation is prompt, phosphorence is delayed fluorescnece.

42
Q

pixel sizes in mammo

A

50-100 um

43
Q

of pixels in mammo

A

15 million

44
Q

does digital mammo always use AEC?

A

yes

45
Q

for processing vs for presentation images

A

for processing: after application of detector corrections
for presentation: after application of vendor specific enhancements that help enhance subcutaneous tissue and skin

46
Q

luminance required for mammo monitors

A

600 cd/m2, view in dark room

47
Q

size of monitors

A

5 MP-8 MP
-5 MP requires using zoom

48
Q

contrast ratio for monitor

A

brightest to darkest pixel
> 300:1 required for mammo

49
Q

optimal viewing distance for mammo

A

50 cm

50
Q

how should monitors be calibrated?

A

DICOM grayscale standard display function

51
Q

how is magnification achieved?

A

move breast away from detector, toward focal spot

air gap reduces scatter from reaching the film and eliminates need for a grid
-removing grid allows mAs to be reduced from 100 to 70

-usually magnify x 2
-SNR improves
-only part of breast is imaged

52
Q

focal spot size in magnification mammo

A

0.1 mm to maximize sharpness

53
Q

tube currents for magnification mammo

A

25 mA

54
Q

exposure times in magnification mammo

A

3 s

55
Q

what does magnification mammo improve visualization of?

A

mass margins
fine calcifications

56
Q

what is breast tomosynthesis?

A

removes overlap of breast tissue in image by creating tomographic imaging

-only shows lesions in a given plane
-acquires a number of projection images, each at a different angle (x-ray tube moves in arc around breast)
-typical arc is 15 degrees, with one image taken at each degree

-compression is used to minimize motion artifact

57
Q

length of breast tomosynthesis exam

A

5 s

58
Q

slice thickness of breast tomosynthesis image, how many tomographs?

A

45 tomographs, 1 mm each

59
Q

radiation dose of breast tomo

A

comparable to contact mammo

60
Q

advantages of breast tomo

A

-detects 40% more invasive cancers
-more promising than dedicated breast CT systems
-similar in plane resolution as 2D imaging, which is better than that of breast CT

61
Q

breast biopsy

A

-patient is prone
-two views of breast are acquired +/- 15 degrees from normal
-biopsy needle gun captures a sample

62
Q

advantages of upright vs prone biopsy

A

upright has better lesion visibility, faster lesion targeting, reduced procedure time

63
Q

what is computer aided detection?

A

-uses algorithms to flag possible findings in digital mammo

64
Q

sensitivity of CAD

A

90%

65
Q

false positive rate

A

2 false positives/image
-attempts to characterize each identified lesion
-assigns likelihood of malignancy

66
Q

what is MQSA?

A

-mammography quality standards act
-requires all mammo facilities in US to be certified every 3 years

67
Q

ACR phantom to assess image quality

A
  • has:
    6 fibers
    5 speck groups
    5 masses

to pass, image must show 4 fibers, 3 speck groups, and 3 masses

68
Q

MSQA requirement for dose

A

average glandular dose for 4.2 cm thick breast phantom must be < 3 mGy/image (with grid)
1 mGy without grid

-if fails, the machine is taken out

69
Q

how do mammo scintillators minimize blur?

A

made of columns

70
Q

MSQA limiting resolution requirement

A

12 lp/mm for screen-film
7 lp/mm for digital (14 pixels/mm)

71
Q

limiting factor for resolution in digital mammo

A

pixel size (70 um)

72
Q

what does higher beam quality do in mammo?

A

-reduce contrast
-reduce dose
-reduce exposure time, minimizing blur

now tungsten being used- higher quality- but contrast reductions are offset with image processning

73
Q

what does breast dose depend on?

A

-breast thickess and glandularity

74
Q

average glandular dose for 60 mm thick breast

A

1-2 mGy per view
-left and right breast doses are never added together
i.e. if each breast gets 3 mGy the patient dose is 3 mGy

75
Q

what does increasing breast thickness by 10 mm do to average glandular dose?

A

double it

76
Q

agd for 80 mm breast

A

> 3 mGy/view

77
Q

by how much do screening programs reduce fatality rate?

A

20%

78
Q

radiation risk from mammo

A

equivalent to risk of dying in an accident when traelling 1000 miles by a car

one million 50-year old women receiving a glandular dose of 3 mGy corresponds to a risk of 6 fatal breast cancers using BEIR VII risk estimates

79
Q

how many cancers are identified by screening 1 million women?

A

4,000, a quarter of them fatal

80
Q

benefits of digital mammo over screen-film

A

ability to process image
-linear response over wide dynamic range

81
Q

smallest microcalcifications seen in mammograms

A

0.1 mm

82
Q

representative HVL for mammo

A

0.5 mm Al

83
Q

reducing SID on mammo would increase what?

A

focal spot blur

84
Q

of pixels in digital mammogram

A

20 million

85
Q

screening a million 50 yo women most likely results in how many fatal-induced cancers?

A

10

4000 cancers detected per million

Huda (20 decks)

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