AbstractID: 9229 Title: Radiographic Techniques for Digital Mammography with an Amorphous
Selenium Detector
Film/screen mammography uses dedicated x-ray systems with Molybdenum (Mo), Rhodium (Rh) or Tungsten (W) targets and Mo, Rh or
Aluminum (Al) filters. The subject contrast that can be obtained from these target/filter combinations is then transformed with high contrast
film/screen systems to provide good radiographic contrast. This requires matching the transmitted radiation intensities from the breast to the
small latitude of these film/screen systems. For digital imaging, the latitude of the detector is much larger and computer processing can be used
to produce the required display contrast. This allows the recorded contrast to noise ratio (CNR) to be independently optimized with respect to
radiographic technique factors.
In this study we modeled the x-ray spectrum and detection characteristics for a digital detector (amorphous
selenium) system and optimized the CNR relative to absorbed dose for several target/filter combinations, kVp ranges and varying breast
thickness. A semi-empirical approach was used to model the x-ray spectrum. A Monte Carlo calculation was used to model breast dose and
detector response. The target/filter combinations included: Mo/Mo, Mo/Rh, Rh/Rh, W/Al, W/Mo, W/Tin (Sn), and W/Silver (Ag). For large
breast thickness the W/Sn combination provides high CNR/mGy1/2 and low mAs/mGy as compared to the other combinations. In addition, the
W/Sn provided a relatively constant CNR/dose over a wider range of kVp values used, suggesting fewer constraints on photo timer systems and
operator errors.