Evaluation of Planar Tomography Using Large Area Planar Positron Imaging System

This study is to evaluate performances of a large area planar positron imaging system (PPIS-4800, Hamamatsu) using planar tomography reconstruction. The oblique angles of lines of response, which influence the imaging performances, vary with the detector-to-detector distance. In this study, distances between detectors were set to 300, 200, 120 mm for evaluating the spatial resolutions and the noise characteristics. The results show that the spatial resolutions are 1.9 mm (X), 1.7 mm (Y), and 12.7 mm (Z) at detector distance 300 mm. Because of the incomplete angles of lines of response for the stationary dual-plane geometry, the resolution in Z direction is much poorer than in X, Y directions. As the detector distance reduced to 200 mm and 120 mm the Z-direction resolutions were improved to 10.2 and 9.0 mm, respectively. However, the resolutions of X direction were degraded to 1.87 and 1.86 mm. The resolutions of Y were degraded to 2.36 and 2.37 mm. As for the image quality, the noise characteristics of 3D planar tomography are comparable to that of 2D planar image, although the total counts were dispersed to more voxels for planar tomography. Phantom images were shown to present detection ability of the PPIS-4800 with planar tomography reconstruction.