X-Ray Tube

maximises PE with <20keV

Mo anode with Mo filter (15-30µm, preferentially eliminates higher energy Bremsstrahlung) with characteristic XRs at 17-19keV operated at kVp ≤28keV

other options Rh + Rh (higher K-edge preferable for thick dense breasts), W + Rh, Mo + Mo/Nb (thin breasts)

focal spot nominal size 0.3mm (actual 0.5mm) to image micro-calcifications (<100µm), but limited tube current (risk of movement artefact, film reciprocity failure)

SID 60-75cm for reduced focal spot blurring, but high demands on tube

exit window of Be, reducing off-focus radiation

anode-cathode angle offset (so beam edge angled straight down to reduce dose to chest from a diverging beam), anode on nipple side (take advantage of heel effect with high current through chest wall side) and directly above chest wall (to reduce cut-off from collimation)

FOV to include all margins of receptor area


reduces scattered radiation, improves contrast by reducing beam hardening, immobilises, unifies breast thickness (lower exposure latitude), reduces absorbed dose (due to lower exposure time)

few mm of polycarbonate or Perspex

dual compression (eg MammoSpot compression device) has spot localisation on top of normal compression



moving grids of carbon fibre for all film-screen mammo except magnification studies

Bucky factor 2-2.5 for grid ratios 4-5:1


detector placed behind cassette to avoid interference with image (due to low keV beam used)

microprocessor measures instantaneous dose rate, and based on selected kV and/or measured breast thickness terminates exposure with reference to LUT (look up tables; separate for each operation mode ie grid/magnification/auto kV etc)

control optical density to ±0.2 of user selected value

auto-kV increases kV within 10-30ms to ensure exposure time not violated


high film contrast with gamma 3.0-3.5

single emulsion film with screen behind film to minimise lateral diffusion of XRs close to film

double emulsion film-screen have front screen ½ thickness of back with very little crossover; useful for magnification but too noisy for contact mammo

limited latitude/dynamic range of 25:1


m=1.5-2 (standard 1.2 or 1.8) improves effective resolution (enlargement of breast relative to film-screen, only if unsharpness from focal spot minimised), reduces effective noise, reduces scatter (due to air gap 16-30cm)

high dose technique due to low SSD (↑skin D by 4x, MGD by 2x)

due to lower focal spot (thus reduced mA possible), kVp may be increased to 30-32 to reduce exposure time

Stereotactic Imaging

FNAB = fine needle aspiration biopsy with 18-20 gauge needle, missing 25% of cancers

core biopsies use larger 14 gauge cutting needles

biopsy gun on vernier driven table for accurate positioning of needle

views of compressed breast taken at two different angles (±15° to imaging plane)

pre-fire position = positions of reference radiopaque markers entered into computer which indicates coordinates for needle placement and two further images taken for verification

post-fire position = to verify final needle position

further films at end to establish number of micro-calcifications removed

prone units have reduced patient motion, reduced vasovagal/fainting episodes

Dose and Screening

MGD = mean absorbed dose to glandular tissue, dependent on breast type, technique, processing; inferred from skin air-kerma with tables; ≤3mGy (ideally ≤2 for 50:50 breast of 5cm thickness)

high dose required for large dense breasts

relative risk and linear dose response models assumed

biennial screening mammo commencing at 40y and 5mGy has lifetime risk of fatal cancer of 27/million; modest reduction in mortality 20%; hence benefit/risk ratio of 310

risk may be higher for larger/denser breasts and no FHx, or much less of hormesis is correct

interpretation of young breasts more difficult due to elevated tissue density

Digital Mammography

for 10lpmm matrix size of 9600 x 7200 required (132Mb for 12bit)

CR has high dynamic range


a-Si flat panel detector arrays using CsI scintillator


TACT (tuned aperture computed tomography) – XR source moves to take 7 different angles (do not need to be predetermined) with a radiopaque reference point for image reconstruction

CT Laser Mammography

fematosecond (10-15s) pulses of IR with primary/ballistic photons reaching detector before the scattered photons

procedure time 10min, spatial resolution <1mm

Computer-Aided Diagnosis

combines artificial intelligence and digital image processing; used as supporting role for radiologist

CADe (computer aided detection) – marks conspicuous structures and sections

CADx (computer aided diagnosis) – evaluates conspicuous structures

CADq – quantifies the lesion with size, contrast uptake etc

Other Techniques

CT useful for breast implant ruptures and breast cancers take up iodine

ultrasound distinguishes cystic from solid and is an adjunct to mammography

MRI with RF-surface coils; Gd-DTPA used; best modality for breast implant rupture


photoconductive (a-Se) plate forms latent electrostatic image for toner (fine powder) to attract; transfer of powder to plastic coated paper followed by thermal bonding

edge enhancement due to particles attracted to region of high charge but poor margins won’t be differentiated hence acts as band pass filter (MTF for high lp/mm > low lp/mm)

plate can instead be scanned with electric charge transducers (electrometers) for digitisation