Performance Comparisons of Continuous Miniature Crystal Element (cMiCE) Detectors

In this paper, we investigated the performance characteristics of continuous miniature crystal element (cMiCE) detectors. Versions with a 25 mm by 25 mm by 4 mm-thick LSO crystal and with a 50 mm by 50 mm by 8 mm-thick LYSO crystal were evaluated. Both detectors utilize a 64-channel flat panel photomultiplier tube (PMT). The intrinsic spatial resolution for the detectors was evaluated using Anger (i.e., simple centroid) positioning and a statistics based positioning (SBP) algorithm. We also compared the intrinsic spatial resolution for the 8-mm-thick LYSO crystal using different reflective materials (e.g., TFE Teflon, white paint, and a polymer mirror film) applied on the entrance surface of the crystal. The average energy resolution was 20% for the 4-mm-thick LSO crystal and ranged from 16% to 21%, depending upon reflective material, for the 8-mm-thick LYSO crystal. The average intrinsic spatial resolution for the 4-mm-thick crystal was 1.8-mm full width at half maximum (FWHM) for Anger positioning to within 3 mm of the crystal's edge and 1.14-mm FWHM for SBP to within 2 mm of the edge. The average intrinsic spatial resolution for the 8-mm-thick crystal was 2.2-mm FWHM for Anger positioning to within 8 mm of the crystal's edge and 1.3- to 1.5-mm FWHM (depending on reflective material used) for SBP to within 2 mm of the edge. Intrinsic spatial resolution is reported without correcting for point source size. The point spot flux had a FWHM of about 0.52 mm. The SBP algorithm resulted in significant improvement in intrinsic spatial resolution, linearity of positioning result, and effective field of view (FOV) for our cMiCE detector

I. Introduction

Discrete crystal detector modules have traditionally been used to achieve high spatial resolution for small animal positron emission tomography (PET) scanners [1]. However, cost goes up considerably as one uses a smaller and smaller cross-section crystal. We have previously investigated a continuous miniature crystal element (cMiCE) detector that comprised a 25 mm by 25 mm by 4 mm-thick slab of LSO coupled to a 26-mm square, cross-anode position sensitive photomultiplier tube (PMT) (Hamamatsu R5900-00-C12, Japan) as a lower cost alternative to high resolution discrete crystal designs [2]. In that work, we introduced a statistics-based positioning (SBP) algorithm, similar to previously proposed maximum-likelihood (ML) methods [3]–[5], which improved the positioning characteristics near the edge of the crystal. We now investigate the performance characteristics using a 52-mm square, 64-channel flat panel PMT (Hamamatsu H8500, Japan). Experimental results were acquired along one axis of the detectors for a 25 mm by 25 mm by 4 mm-thick slab of LSO (CTI, Knoxville, TN) and a 50 mm by 50 mm by 8 mm-thick slab of LYSO (Saint Gobain, Newbury, OH).