Design, development and characterization of a full-field digital mammography detector.

摘要

A 3 x 2 CCD based x-ray detector for full field digital mammography (FFDM) imaging has been designed, developed and characterized to meet the requirements imposed by mammographic imaging: high contrast detail, high spatial resolution, and low dose. It consists of a 29-cm x 18-cm GdO 2S2 phosphor screen closely coupled to six tiled fiber-optic tapers permanently bonded to six high-resolution CCDs. The design and construction of this digital detector could serve as a guide for the development of similar detectors for other applications in medical diagnostic imaging.The theoretical work presented uses a cascaded linear systems approach to determine the detective quantum efficiency (DQE) as a function of spatial frequency by describing each stage of the detector as introducing gain or blur as the signal and noise propagate through the system. This model was experimentally verified and the results closely match the shape and magnitude of the theoretical DQE. It was found that the DQE is almost completely invariant with respect to energy and exposure. At zero frequency the detector reaches a maximum DQE of &sim45% and drops of to &sim25% at 5 lp/mm and to &sim5% at the Nyquist frequency for a range of exposures less than &sim100 MR and energies between 25--30 kVp. This result is superior to that of current screen-film systems and, therefore, it is expected that mammographic imaging done with this FFDM detector will be greatly improved.The diagnostic accuracy of the system was also evaluated and compared to that of a screen-film system by performing a receiver operating characteristic (ROC) curve analysis using a mammographic statistical phantom (ALVIM TRM). It was found that for a 7.5-cm simulated breast of nonuniform composition the area under the ROC curve, Az, which is a good descriptor of diagnostic accuracy, was &sim9% higher for screen-film than for the FFDM system. This is explained by the lack of a scatter rejection grid for the FFDM system. Technique factors (kVp and mAs setting) for clinical imaging using the FFDM system were obtained for a range of clinically relevant mammographic energies using phantoms of different breast equivalent tissue compositions and thicknesses.