SU‐D‐301‐05: Angular Dependency of the Slice Sensitivity Profile in Tomographic Breast Imaging

Abstract

Purpose: To study the effect of angular acquisition on the slice sensitivity profile (SSP) in tomographic breast imaging, for both breast CT and tomosynthesis. Methods: Brass disks (0.025 mm thick) ranging in diameter from 2.5–20 mm were placed within mammography phantoms of varying thicknesses (3–6 cm). The disks were imaged using a prototype digital tomosynthesis system (Selenia Dimensions, Hologic Corporation, Bedford, Ma). The tomosynthesis system acquires images over an angular acquisition range of 15‐degrees. The same brass disks were used to measure the SSP in breast CT, using a 14cm‐diameter cylindrical polyethylene phantom. The bCT angular range spanned from 15 to 360‐degrees. A subset of the projection images were reconstructed with a filtered back projection algorithm to simulate limited‐angle acquisition. The SSP was determined by measuring the mean gray‐scale (GS) in the tomographic images along the z axis of the scan corresponding to the disk position. Normalized profiles of the background‐corrected mean GS values were generated as a function of the distance away from the detector. The full‐width at half maximum (FWHM) GS intensity was determined. Results: As the angular acquisition range increases, the SSP narrows and results in a smaller FWHM value. The FWHM values of the SSP for the smallest disk at (2.5 mm‐diameter) were 8.6 mm, 4.2 mm, and 0.8 mm for 15, 40, and 180 degrees, respectively. Conclusions: Limited angle tomography results in a broadening of the SSP, inversely proportional to the angular range of acquisition. The SSP approaches a minimum as the angular coverage exceeds 180 degrees.One author receives funding from Hologic (Bedford, Mass).