Mammography Flashcards

1
Q

Core issues of mammo

A

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

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2
Q

Mammo geometry

A

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

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3
Q

Mammo x-ray tube

A
  • 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

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4
Q

Impact of filtration

A
  • Removes low E photons
  • reduces skin dose
  • increases mean energy of beam
  • K edge filters generally used for mammo
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5
Q

Effect of k-edge filter

A
  • Filter is relatively transparent below the k-edge
  • > char x-rays transmitted
  • Signif atten of bremstrah above k-edge
  • increases contrast
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6
Q

Benefits of compression

A
  • Immobilises breast
  • Reduces the dose
  • Improves image quality
  • Reduces scatter within the breast - thinner tissue
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7
Q

Compression systems

A

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

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8
Q

Define AEC

A

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

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9
Q

AEC types

A

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

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10
Q

Mammo detector type

A

Mainly a-Se and CsI with a-Si

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11
Q

Advantages and limitations of DR mammo

A
• Better contrast
performance
• Larger dynamic range
• Improved dose efficiency
• Imaging processing
• PACS
• Lower resolution
• Start-up costs
• Image processing
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12
Q

Advantages and limitations of film mammo

A
Analogue
• Contrast-latitude
compromise
• Limited dynamic range
• No post processing
• Stability of film processing
• Proven technology
• High resolution
• Affordable
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13
Q

DR spectrum

A

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

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14
Q

Phillips sys

A

Collimator defs many thin beams which scan accross

No need for a grid

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15
Q

Photon counting det features

A

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

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16
Q

Measurement of mammo dose

A

Mean glandular dose - at-risk dose

ESD doesn’t take into account changes at depth

17
Q

Measurement of breast dose

A
  • Simulated with PMMA blocks - QA
  • Dose surveys
  • Calculate entrance surface air kerma
  • Derive MGD using HVL and composition dependent conversion factos
18
Q

NDRL

A

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

19
Q

Define sterio-tactic mammo

A

Ass-on for standard mammo or dedicated

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

For placing guide wires

20
Q

Digital breast tomosynthesis

A
  • 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

21
Q

Breast cancer incidence

A

1 in 8 with will develop breast cancer

22
Q

Patient screen requirements

A

Originally aged 50-64 every 3 years

2005: 50-70 every 3 years, 2 views
2016: 43-73 every 3 years

23
Q

Issues with younger women

A

Less common
Harder to image
Increases risk of induction from screening

24
Q

Protocol for older women

A

Routine invited stop at 70

Can still attend though

25
Q

Risk vs benefit

A

Risk 1: Induced per 14,000 screen 3 times over 10 years (aged 50-70)

Benefit 1: 1 saved for every 400 over 10 years

26
Q

IRMER referral

A

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

27
Q

IRMER just/auth

A
  • Radiologist, breast clinician or breast screening radiographers
  • Identity of women and eligibility confirmed before authorising exposure
  • Consider previous screening history
  • Record kept that woman meets local and national criteria
  • Record confirming that examination has be justified, authorised and by whom
28
Q

Exemptions to standard protocol

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