Abstract
Phase contrast imaging is characterized by edge-enhancement of objective image boundaries. The conditions of geometric unsharpness, i.e. the focal spot size of an X-ray tube and the relation between the focus-object distance R1 and object-detector distance R2, are important factors in edge-enhancement. In this study, we investigated the following two issues: First, evaluation of the magnification factor that yields maximum edge-enhancement effect; second, an evaluation of the sampling pitch of digitization without loss of the edge-enhancement effect. For this purpose, we imaged a plastic-fiber of 3.0mm in diameter using various magnification factors and a screen-film system as the detector. We considered that the optimum magnification factor would be the one to yield the strongest edge-enhancement, and that the optimum sampling pitch size would be the one which retained the same degree of edge-enhancement as reflected by an “analog" profile curve of the plastic-fiber image. As a result, the optimum magnification ratio was found to be 1.75times, when R1 was 65cm using an X-ray tube of 0.1mm focus spot size. We also found that edge-enhancement in phase contrast imaging can be effectively achieved with digital imaging when acquired with a sampling pitch of 0.025mm or less.
