In-plane spatial resolution measurements of a phase-contrast tomosynthesis prototype

Abstract

The objectives of this project are to intrinsically and quantitatively investigate the advantages of a phase-contrast (PC) tomosynthesis prototype in removing the superimposed structure noise and the effects on image qualities by an off-center shift of the object along the tube-sweep direction. Experimentally, phantoms are assembled with standard resolution patterns. Phase-contrast tomosynthesis images are acquired and reconstructed. In order to study the effects of the limited angular projections on the in-plane resolutions, all the images were reconstructed in the 2×2 binning mode only, as we will study the phase contrast effects elsewhere. The in-plane slices reconstructed from each of the experiments examined and the in-plane limiting resolutions are determined. For comparison, the resolution patterns and phantoms are also imaged by single projections. Under single x-ray projection, with only one resolution pattern, the limiting resolution of the system is 8 lp/mm; with 2 resolution patterns superimposed, the image of the resolution patterns is blurred for distinguishing line pairs. The PC tomosynthesis in-plane images show that the limiting resolution of the system is 7 lp/mm. For objects with a shift along the horizontal axis (the tube-sweep direction) by 0.8 inch, the spatial resolution is degraded to 4 lp/mm and blur occurs. As is expected, the PC tomosynthesis prototype studied in this project reveals superimposed fine structures of the object; the effect induced by the object's off-center shift is determined in a quantified way. The in-plane resolution of this system can be further improved by optimizing the system alignment, and the reconstruction algorithms.