Using aluminum for scatter control in mammography: preliminary work using measurements of CNR and FOM

Full-field digital mammography (FFDM) systems provide the current gold standard in mammographic examinations. Although FFDM provides the lowest mammographic doses, the radiation dose to the breast during mammographic examinations is still a concern. Thus, image quality optimization at the lowest dose is a major goal. In planar X-ray imaging, thin sheets of aluminum (Al) are used as filtration to reduce the number of low-energy X-ray photons reaching the patient. The goal of this work was to evaluate whether Al can be used in FFDM to remove scatter radiation from reaching the image detector, hence improving image quality. Doses were compared with the use of a grid. A Hologic Selenia mammographic unit was used to acquire images of two phantoms, namely, the ACR phantom and a Perspex phantom of 5 cm. Images were acquired using two tube voltages (kVp) and filter combinations under two exposure/dose conditions. Al sheets of various thicknesses were placed between the phantom and the image detector. Contrast-to-noise ratio (CNR) and figure of merit (FOM) values were measured and compared with images acquired using a grid. When a constant dose was delivered to the image detector, the highest CNR was achieved using a grid; however, the highest FOM values were achieved when using 0.05 mm thick Al sheets. This study successfully demonstrates that thin sheets of Al can be used in mammography examinations to reduce scattered radiation and improve image quality, as indicated by the measured CNR values. Given the limitations of this work, further kVp and target/filter combinations and various methods of image quality measurement need to be studied.