Imaging characteristics of plastic scintillating fiber screens for mammography

A scanning slot digital mammography system using a plastic scintillating fiber screen (SFS) is currently being developed. To improve the x-ray interaction efficiency and absorption efficiency of an SFS, high Z elements can be added into the scintillating fiber core. In this paper, we investigate theoretically the zero spatial frequency detective quantum efficiency, DQE(0), and modulation transfer function, MTF(f), of three 2 cm thick SFSs made of polystyrene, polystyrene loaded with 5% by weight of lead, and polystyrene loaded with 10% by weight of tin scintillating fibers. X-ray interaction efficiency, scintillating light intensity distributions and line spread functions were generated using Monte Carlo simulation. DQE(0) and MTF(f) were computed for x-ray energies ranging from 15 to 50 keg. Loading high Z elements into the SFS markedly increased the DQE(0). For x-ray energies used for mammography, DQE(0) values of both high Z element loaded SFSs are about a factor of three higher than the DQE(0) of an Min-R screen. At mammographic x-ray energies, MTF(f) values of all three SFSs are greater than 50% at 25 lp/mm spatial frequency, and were found to be dominated by the 20 micrometer individual scintillating fiber diameter used. The results show that both high DQE(0) and spatial resolution can be achieved with the high Z element loaded SFSs, which make these SFS attractive for use in a scanning slot detector for digital mammography.