Dynamic Contrast-Enhanced Digital Breast Tomosynthesis

PURPOSE The purpose of this work is to characterize the spatial dependence of the in-plane 35 modulation transfer function (MTF) in tomosynthesis and investigate the influence of the acquisition geometry. METHODS The in-plane MTF was calculated from measured edge spread functions using a custom 40 test tool consisting of a 0.250 mm thick lead sheet affixed to a 5.88 mm acrylic sheet. Images were obtained using a non-clinical bench-top tomosynthesis system; reconstructions were performed using customized commercial software. The dependence of the MTF was measured with respect to the following factors: 1) the offset of the reconstruction plane from the plane containing the edge; 2) the obliquity of the 45 reconstruction plane with respect to the detector; 3) the number of projections per reconstruction; and 4) the acquisition's angular range. Findings were validated by developing an analytical model of the MTF (accounting for blurring due to focal spot size, magnification, reconstruction pixel size, out-of-focus plane, and reconstruction blurring) and by replicating the experiment on a clinical tomosynthesis system. 50 RESULTS The MTF is degraded when the edge is located between two reconstruction planes. The degree of degradation of the MTF increases as the distance between the edge and the reconstruction plane increases and as the angular range of acquisition increases. 55 Degradation increases very slightly as the obliquity of the reconstruction plane with respect to the detector increases over the range 0o to 32o. The number of projections per reconstruction does not affect the degradation. The simulated MTFs generated by the analytical model were concordant with findings of the MTF degradation factors, and a validation experiment on a clinical tomosynthesis system provided independent 60 confirmation that the MTF degrades with increasing distance between the edge and the reconstruction plane. CONCLUSION The MTF of tomosynthesis systems is spatially anisotropic and varies with sub-slice 65 spacing. Reconstruction of oblique planes results in minimal degradation of the MTF and thus may be clinically acceptable.