filter placed outside of tube to create mono-energetic beam ( 20 filtered out)

5. Mammo Flashcards by Eleanor Yu

difference in mammo XR

lower energy monoenergetic beam to enhance attenuation differences
increase in spatial resolution to see microcalculations

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mammo – optimal kVp

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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mammo – target, characteristic x-rays

mammo uses molybednum or rhodium anode

moly: 18 keV ; rhodium: 20.2 keV

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why is moly used for mammo

low atomic number, generate low K characteristic x-rays

peak characteristic x-rays with low Bremsstrahlung

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k-edge filtration

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

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when is Rh vs Mo used?

Rh used for denser breasts since it’s higher energy

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why would Mo anode and Rh filter be used?

intermediate energy spectrum

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

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when is Mo anode used with aluminium filter?

harder beam to penetrate denser breasts

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

increases average energy of beams

reduces contrast

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mammo – focal spot size

0.1-3 small; better spatial resolution

general x ray 0.6-1.2 mm

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problems with small focal spot size

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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mammo – exposure time

longer than xray

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

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

cathode goes on chest wall

tube angled up 20 degrees

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effective anode angle

effective anode angle = anode + tube tilt angle

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diagnostic tube for mammo vs xr?

mammo: beryllium exit window (less attenuation)

Dx: glass

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reason for breast compression in mammo?

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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antiscatter grid in mammo

4-5 grid ratio (height/width)

smaller grid ratio and lower kVp (reduces scatter)

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problems with grid

increased dose with grid since grid removes scatter

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bucky factor for mammo vs XR

mammo: 2
XR: 5

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mag view of breast?

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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is there a grid in mag view?

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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major changes with mammography and XR

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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difference between mammo and mag view

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

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optical density in mammo

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

air kerma? relationship with distance

density of xrays ; decreases via inverse square law with distance

entrance air kerma

radiation incident on patient

receptor air kerma

radiation used to generate image

which is bigger, entrance vs receptor air kerma?

receptor AK less than entrance

air kerma in mammo

higher than in general XR usually because source to image distance is much smaller in mamms compared to DX

digital mammo vs analog with spatial resolution?

digital systems have lower spatial resolution

is there a specific line pair requirement MQSA for digital?

no; manufacturers specifications

digital mammography dose?

less than analog ~15% because of better beam quality

digital mammography noise?

fixed after exposure is taken dark noise: electronic fluctuations within detector element; proportional to temperature of detector

flat field test

imaging acrylic to improve image quality and calibrate digital detectors

ghosting in mammo

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

pixels gone bad

square or streak

digital artifacts in mammo

ghosting, pixels gone bad

digital breast tomosynthesis

stacked images taken in 15 prjections that decreases the effects of tissue superimposition improves sensitivity/specificity

pros/cons of DBT

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

PPV

positive predictive value proportion of people with a postive study who have breast cancer positive exam / (all positive exams--cancer and overcalls)

benchmark for PPV1

positive screening -- BR 0, 3-5 or call backs benchmark -4.4.%

benchmark for PPV2

callbacks where biopsy recommended -- BR 4-5 benchmark - 25.4%

benchmark for PPV3

results of biopsy; positive biopsy rate , biopsy yield of malignancy benchmark: 31%

how often is mammo accredited/certified?

3 years

who monitors MQSA

FDA

who is responsible for QA and QC per MQSA?

interpreting physician

minimum megapixels on a mammo workstation

3 MP

target range for medical audit: recall rate

5-7%

target range for medical audit: cancers/1000 screened

3-8

processor QC frequency

daily

darkroom cleanliness frequency

daily

viewbox conditions frequency

weekly

phantom evaluation frequency

weekly

repeat analysis frequency

quarterly

compression test frequency

semi-annually

darkroom fog frequency

semi-annually

screen-film contrast frequency

semi-annually

mammo requirements

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

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

anode-cathode: 13 LP/min left-right: 11 LP/min

MQSA requirmeents for screen film and manufacture spects for digital?

12 lp/mm for screen-film manufacture specs for digital ~7 lp/mm

breast phantom specs

4.2 cm of breast tissue is 50% adipose/glandular

average compressed breast thickness/glandularity in the US

60 mm, ~15% glandularity

phantom mammo limit

3 mGy with grid | 1 mGy w/o a grid