Mammography Flashcards
List 5 features of a Mammography unit
- Angled tube
- Filter assembly
- Fixed collimator
- X-ray beam
- Digital detector
- Compression paddle
- Table bottom
- Breast support platform with (grid)
Why is the target anode made from Molybdenum and Rhodium?
- They produce characteristic X-rays which are better for contrast
- At low kVp, the emission spectrum contains more low energy X-rays which are suitable for breast tissue
- Allow increased subject contrast of breast tissue (good for breast tissue because it has low subject contrast)
Why does breast tissue have low subject contrast?
The soft tissue attenuates the X-ray beams similarly because the density is alike across the breast.
In what ways does filtration improve image quality?
- Absorbs the lowest and highest energies, leaving only optimum X-ray energies (monoenergetic beam)
- Enhances contrast sensitivity
- Uses Mo, Rh, Ag and Al
What kV technique is used in Mammography and why?
Low kVp technique.
Is used because breast tissue has low subject contrast and has similar density tissue which makes it difficult to distinguish between breast, glandular & fat tissue.
List 4 advantages of DBT
- Non-invasive
- Reduces superimposition of tissue with similar attenuation
- Relatively low dose
- Dense and glandular breast visualisation
- Less need for biopsy bc of reconstructions
List 4 disadvantages of DBT
- Specific training required
- Longer scanning time
- Higher radiation dose to patient
- Longer to report/interpret
- IT/Storage issues
What is Digital Breast Tomosynthesis (DBT)
Higher dose than conventional mammogram
3D reconstructions of whole breast
Images taken at different angles
Low dose relative to CT
Used only on affected breast
DBT is…
- …a 3D mammography technique
- …a simple and efficient procedure
- …useful for imaging sensitive breasts
- …computerised reconstruction
Why are high mAs used in mammography?
To generate more X-ray photons to compensate for their low penetrating power (at low kVp)
How does a low kVp affect radiation dose?
A higher mAs is required which means more photons are needed, therefore increasing radiation dose.
Define and explain the Anode Heel Effect.
The anode heel effect is the varying intensity of the X-rays across the beam.
- The intensity of the X-ray beam is less on the anode side which is why angling the target exaggerates the variation in X-ray beam intensity.
- This is beneficial because of the varied thickness between the chest wall and the nipple edge.
- Increased beam intensity = Increased penetration
How is contrast increased and why does this contradict the low kVp technique.
Contrast is increased by using an X-ray spectrum of low energy photons which generates low patient dose. The low kV technique, however, increases patient dose due to the high mAs.
An X-ray beam that produces an optimum balance between the high contrast and low dose requirements is needed.
Perks of Low kV technique
- Maximises photoelectric interactions
- Improves contrast resolution
- Minimises Compton scatter
- More radiation exposure
