Brian Curtis Lee, Presenter: Nothing to Disclose

Raymond Acciavatti, Abstract Co-Author: Nothing to Disclose

Andrew D.A. Maidment PhD, Abstract Co-Author: Research support, Hologic, Inc Research support, Barco nv Spouse, Employee, Real-Time Radiography, Inc Spouse, Stockholder, Real-Time Radiography, Inc

To characterize the spatial dependence of the in-plane modulation transfer function (MTF) in tomosynthesis and investigate the influence of the acquisition geometry.

The in-plane MTF was calculated from measured edge spread functions using a custom 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 benchtop tomosynthesis system; reconstructions were performed using customized commercial software (Briona, RTT Inc., Villanova PA). 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 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, detector element size, out-of-focus plane, and reconstruction filter) and by replicating the experiment on a clinical tomosynthesis system.

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. 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 on the MTF degradation factors, and the validation experiment on the clinical tomosynthesis system provided independent confirmation that the MTF degrades with increasing distance between the edge and the reconstruction plane.

The MTF of tomosynthesis systems is anisotropic and varies with sub-slice spacing. Reconstruction of oblique planes results in minimal degradation of the MTF and thus may be clinically acceptable.

Sub-slice misalignment of objects with the reconstructed DBT slices may adversely affect the conspicuity of small clinical features such as calcifications.

Lee, B, Acciavatti, R, Maidment, A, Characterization of the Dependence of the Modulation Transfer Function in Tomosynthesis on Acquisition Geometry and Reconstruction Parameters.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13027647.html