Simulation of high-resolution test objects using non-isocentric acquisition geometries in next-generation digital tomosynthesis.

Abstract

Digital breast tomosynthesis (DBT) systems utilize an isocentric acquisition geometry which introduces imaging artifacts that are deleterious to image reconstructions. The next-generation tomosynthesis (NGT) prototype was designed to incorporate various x-ray source and detector motions for the purpose of investigating alternative acquisition geometries for DBT. Non-isocentric acquisition geometries, acquisitions that vary the image magnification between projection images, are capable of ameliorating aliasing and other artifacts that are intrinsic to conventional DBT. We used virtual clinical trials (VCTs) to develop custom acquisition geometries for the NGT prototype. A high-resolution (5μm voxel size) star pattern test object was simulated to compare the high-frequency performance of isocentric with non-isocentric image reconstructions. A tilted bar pattern test object was also simulated to compare multiplanar reconstructions (MPR) of isocentric and non-isocentric acquisition geometries. Two source- and detector-motion paths were simulated to obtain super-sampled image reconstructions of the test objects. An aliasing-sensitive metric was used to evaluate spatial resolution performance for two orthogonal frequency orientations. Pairwise comparisons were made for the two frequency orientations between the isocentric and non-isocentric acquisition geometries. Non-isocentric acquisition geometries show an improvement over isocentric acquisition geometries. The greatest improvement was 75.2% for frequencies aligned perpendicular to x-ray source motion, which is the direction of frequencies for which DBT is prone to aliasing. Both frequency orientations exhibit super resolution for non-isocentric geometries. MPR of the tilted bar pattern show z- dependent degeneracies for the isocentric acquisition only, whereas MPR of the non-isocentric acquisition entirely exhibits super resolution.