| Target |
- In addition to tungsten, molybdenum and rhodium used as target materials
| Material |
K-shell e- binding energy (keV) |
K-shell characteristic x-ray (keV) |
| Tungsten |
69.5 |
59.32 |
| Molybdenum |
20.0 |
17.48 |
| Rhodium |
23.2 |
20.22 |
|
| Filtration |
- Molybdenum & rhodium used as filters
- Take advantage of filter's k-edge to shape spectrum for optimum subject contrast
- Mammography tubes usually have beryllium windows
- Less filtering
- Reduces beam energy increase for improved subject contrast of breast
- Many mammography systems calculate and insert filtration required for optimum beam spectrum
|
| Tube port (window) |
- Beryllium replaces glass
- Reduced
- attenuation of beam to maximize radiation output
- filtering of beam to improve subject contrast
|
| Exposure parameters |
- Tube current
- significantly less than radiography
- further reduction in mA for magnification (small focal spot)
- Kilovoltage
- significantly less than radiography
- improves subject contrast
- Source to image distance (SID)
- significantly less than radiography
- compensates for low beam intensity due to smaller focal spot size
|
| Magnification |
- Small focal spot used
- recovers spatial resolution lost by magnification of 1.2-2.0
- reduces penumbra
- requires lower mA resulting in longer exposure time
- Scatter radiation reduced using air gap instead of grid
- Increases dose
- Reduced spatial resolution
- Improved effective resolution
|
| Heel Effect |
- Highest radiation output to thickest part of breast (chest wall)
- Anode-cathode axis oriented in anterior-posterior direction
- Cathode side of tube closest to patient
|
| Compression |
- Decreases scatter
- Decreases geometric blurring
- Decreases superimposition
- Decreases patient motion
- Decreases exposure time
- Decreases dose
- Increases uniformity of breast thickness
|
| Grid |
|
| Film/screen/cassette |
- Typically single emulsion film
- Single screen above film
|
| Digital Mammography |
- Direct: amoryphous selenium
- Indirect: CsI, CR
|
Mammography 