Mammography (Erin) Flashcards
Why is the breast tissue compressed during image?
Decreases the scatter in the image
Reduces required radiation dose
What size is the broad focal spot mammo?
0.3mm
What is the size of the fine focus focal spot in mammo?
0.1mm
In mammography why is the patient positioned with their chest wall towards the cathode?
To reduce the effect of the anode heel effect
What is the typical tube voltage used in mammo?
25-35kVp
What is the normal compression forced used in mammo?
100-150N
What is the predominant effect utilised in mammography to achieve contrast?
Photoelectric effect
What are the two most common anode material targets used in mammo?
Molybdenum (Mo)
Rhodium (Rh)
What are the 3 different combinations of target/filter used in mammo?
Mo/Mo
Mo/Rh
Rh/Rh
Is Rh/RH (target/filter) used for imaging smaller or larger breasts?
Imaging larger breasts
What is the maximum compression force that can be applied to the breast?
200N
Standard is 100-150N
What are the characteristic xray energies produced from an Mo target?
17.5 and 19.6keV
What is the fixed focus-detector distance used in mammo?
65/66cmcm
Should the anode target used in mammo have low or high keV characteristic xrays? And why?
Low keV
To promote the photoelectric effect
What are the characteristic energies produced from an Rh target?
20.2 and 22.7 keV
Why is a Rh/Mo target/filter combination not used in mammo?
Because the Mo filter would attenuate the Rh characteristic xrays
What is the typical resolution (in lp/mm) in mammography?
10 lp mm
What is the mammo filament length?
0.3-0.4mm
Mammography spatial resolution is limited by…?
pixel size
T/F: The patient dose will be lower when using a digital mammography unit as compared to an analogue unit
True because of the detection efficiency
Is Mo/Mo target/filter combination typically used to image larger or smaller/normal sized breasts?
Smaller/normal sized breasts
What are the characteristic radiation energies released from Mo
K alpha - 17.5 keV
K beta - 19.6 keV
What are the characteristic radiation energies released from Rh
K alpha - 20.2 keV
K beta - 22.7 keV
What is the K edge of Mo
20 keV
What is the K edge of Rh
23.3
In mammo magnification views how is scatter reduced
Breast support table is moved above the film to give magnification views
Large air gap between the breast and the film works to reduce the scatter (so no grid is needed)
How are mammo magnification views obtained
Breast support table is moved above the film to give magnification views
What 3 factors help to improve spatial resolution in mammo?
Small focal spot size
Compression of breast tissue
Anti-scatter grid
What is the purpose of compression in mammo? (6)
- Lowers patient radiation dose (lower attenuation)
- Reduces scatter
- Spreads tissues out so there is less overlaying features
- Reduced geometric unsharpness (by moving tissue closer to object)
- Reduced movement unsharpness by holding the breast still
- Compressed breast is of more uniform attenuation
What is the typical average dose per film?
1.5-3mGy
What is tomosynthesis?
Movement of xray tube and detector to obtain different angle shots
Why is tomosynthesis useful?
To separate structures which lie on top of one another
Tomosynthesis dose is much higher than standard mammography- T/F?
False
All the angles projections are very lose dose. The sum is no more than 2 mammography doses.
Tomosynthesis wider arc angle gives what 2 properties?
Improved contrast
Thinner slices
Tomosynthesis: 4 uses?
Mammography
Lung nodules
Scaphoid imaging
Dental imaging
What is the typical pixel size and spatial resolution in mammo?
Pixel size = 50 micrometers
Spatial resolution = 10lp/mm
What is the population risk of fatal cancers for women undergoing mammography aged 50-65?
1 in 50,000
