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Medical Physics 2: Radiology > Mammography & screening > Flashcards

Flashcards in Mammography & screening Deck (28)
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Core issues of mammo

1) Low tissue contrast
2) Subtle distortions in breast architecture
3) looking for small object - micro calcs ~0.1mm


Mammo geometry

1) FIxed geometry - except in mag
2) Uses anode heel effect
3) Small focal spot


Mammo x-ray tube

- Small focal spot
- Low kV (25-35kVp)
- Mo, Rh or W annode
- Mo, Rh Ag or Al filter
- Anode heel effect reduces intensity at nipple edge.

Mostly W target now


Impact of filtration

- Removes low E photons
- reduces skin dose
- increases mean energy of beam
- K edge filters generally used for mammo


Effect of k-edge filter

- Filter is relatively transparent below the k-edge
-> char x-rays transmitted
- Signif atten of bremstrah above k-edge

- increases contrast


Benefits of compression

- Immobilises breast
- Reduces the dose
- Improves image quality
- Reduces scatter within the breast - thinner tissue


Compression systems

Pre-compression : Position before full compression
Tilting paddles: conform better.
Compressibility detection available
Shifting paddle: L-R adjustment


Define AEC

Controls amount of radiation at the detector

Ensures correct exposure regardless of thickness / composition

Not used with implants

Must work with vary low rad level due to attenuation


AEC types

Basic: mAs

kV selection: dose rate det select on test shot
Adjust based on dose rate

Full auto: filt/voltage based on test shot
target/ filt/volt based on breast thickness
All based on test shot


Mammo detector type

Mainly a-Se and CsI with a-Si


Advantages and limitations of DR mammo

• Better contrast
• Larger dynamic range
• Improved dose efficiency
• Imaging processing
• Lower resolution
• Start-up costs
• Image processing


Advantages and limitations of film mammo

• Contrast-latitude
• Limited dynamic range
• No post processing
• Stability of film processing
• Proven technology
• High resolution
• Affordable


DR spectrum

Harder more pen beam
reduction in contrast but can inc depth dose to compensate
Film would get too dark, lower patient dose while maintaining im quality


Phillips sys

Collimator defs many thin beams which scan accross

No need for a grid


Photon counting det features

Electronic noise effectively eliminated
• Secondary carrier noise eliminated
• Digitisation noise eliminated
• DQE potentially improved due to good detection
efficiency coupled with less detector noise
• Response has to be very quick


Measurement of mammo dose

Mean glandular dose - at-risk dose

ESD doesn't take into account changes at depth


Measurement of breast dose

• Simulated with PMMA blocks - QA
• Dose surveys
• Calculate entrance surface air kerma
• Derive MGD using HVL and composition dependent
conversion factors



for 50-60mm thick breast NDRL is < 3.5mGy


Define stereo-tactic mammo

Add-on for standard mammo or dedicated

Uses two images recorded at different angles, combined to give depth information - via ref point matching

For placing guide wires


Digital breast tomosynthesis

• X-ray tube moves in an arc about a pivot point
• Breast and detector (in general) do not move
• Acquire a series of low dose projections
• Computer reconstructs data into slices at different depths in the breast

removes effect of overlying anatomy

large datasets


Breast cancer incidence

1 in 8 women will develop breast cancer


Patient Screen requirements

Originally aged 50-64 every 3 years

2005 - 50-70 every 3 years, 2 views

2016 - 43-73 every 3 years


Issues with younger women

less common
harder to image
increased risk of induction from screening


Protocol for older women

- Routine invites stop at 70
- Can still attend though


Risk vs benefit

Risk : 1 induced per 14000 screened 3 times over 10 years (aged 50-70)

Benefit : 1 saved for every 400 over 10 years


IRMER refferal

Women invited (referred) for screening if they meet the referral
criteria in the Cancer Reform Strategy document. Invitation letter
is signed by director of screening centre (or lead radiologist). No
individual signed request.


Irmer just / auth

• Radiologist, breast clinician or breast screening radiographers
are practitioners
• Identity of woman and eligibility confirmed before authorising
• Consider previous screening history
• Record kept that woman meets local and national criteria
• Record confirming that examination has been justified,
authorised and by whom.


Exemptions to standard protocol

Women who have recently been screened
• Women who attend without invitation
• Women over current age range
• Partial examinations
• Technical recalls and repeats