Mammography Physics Flashcards
(77 cards)
Be aware that fibrous tissue and cancer have similar attenuation coefficients
What is the difference between breast tissue composition in older and younger breasts
Larger/older breast = higher fat content
Younger breast = tends to be fibro glandular
How does high glandularity of breast tissue affect the sensitivity and specificity
High glandularity limits the sensitivity and specificity of
What is high glandularity
Lots of fibrous tissue
What does sensitivity and specificity mean in terms of breast tissue
Sensitivity - ability to identify cancer
Specificity - ability to identify normal/benign properties
What are the 3 types of tissue found in the breast
Glandular
Fibrous
Adipose tissue
Compare the variation of attenuation coefficient with kV of carcinoma, fibrous tissue, fatty tissue
Carcinoma has the highest linear attenuation coefficient at a certain photon energy, then fibrous tissue then fatty tissue at the same photon energy
What type of energy is needed for mammography and why
Low energies are required to provide adequate contrast in image
Where would the automatic exposure chamber be found on the mammography machine
Positioned in area of typical high density breast tissue
What effect does mammography utilise
Anode-heel effect
What are the 3 different filter materials used in mammography
Molybdenum (k-edge 20kev)
Rhodium (k-edge 23kev)
Tungsten (W) (k-edge 69kev)
What material is the window of the mammography made of
Beryllium
Know that mammography uses shorter SID than xray
What is the size of the fine focal spot of mammography
0.1-0.3mm
Find a diagram of a mammography and label the different parts
- angulation indicator scale
- tube head
- face guard
- compression device
- cassette holder
- AEC chamber
- automatic release foot pedal
- up and down movement controls
Describe what the anode heel effect is
- anode is angled
- photons that hit the anode end have further to travel to exit anode hence form lower energy X-rays
- photons at anode angle/cathode end have less material to travel through to exit anode hence form higher energy xrays
- overall this forms a spectrum of xray energies increasing in energy as it travels up the angle of the anode
Explain how the attenuation of xrays work in mammography / how patient absorbs dose
- xray bream travels through tissue, low energy xray give their energy more easily than high energy xray
- absorption of energy of xray gives the dose to the patient
Why is the patient dose in mammography greater than regular xray
Low energy xrays need to be used for better contrast hence more xrays are required to get the image which increase dose
What concept/ principle brings about image formation in mammography
Different tissues attenuate xrays by different amounts providing our image
Be aware that at low energies, the difference between tissues is greater. So low energies give more contrast.
Hence, you must balance between dose and contrast
What is the purpose of anode rotation in mammography
Heat dissipation
Know that in mammography we can have filter combination/targets, give an example
Molybdenum and rhodium
What is the purpose of filter combination in mammography
for the spectral shaping of the beam for a given target (anode), which affects image contrast and radiation dose
- e.g W/Rh combination filter is used to produce higher energy xray beam
What is k-edge
the abrupt increase in the photoelectric absorption of x-ray photons observed at an energy level just beyond the binding energy of the k-shell electrons of the absorbing atom.
