High-Resolution L(Y)SO Detectors Using PMT-Quadrant-Sharing for Human and Animal PET Cameras

We developed high resolution L(Y)SO detectors for human and animal PET applications using Photomulti- plier-quadrant-sharing (PQS) technology. The crystal sizes were 1.27 times 1.27 times 10 mm³ for the animal PQS-blocks and 3.25 times 3.25 times 20 mm³ for human ones. Polymer mirror film patterns (PMR) were placed between crystals as reflector. The blocks were assembled together using optical grease and wrapped by Teflon tape. The blocks were coupled to regular round PMTs of 19/51 mm in PQS configuration. List-mode data of Ga-68 source (511 keV) were acquired with our high yield pileup-event recovery (HYPER) electronics and data acquisition software. The high voltage bias was 1100 V. Crystal decoding maps and individual crystal energy resolutions were extracted from the data. To investigate the potential imaging resolution of the PET cameras with these blocks, we used GATE (Geant4 Application for Tomographic Emission) simulation package. GATE is a GEANT4 based software toolkit for realistic simulation of PET and SPECT systems. The packing fractions of these blocks were found to be 95.6% and 98.2%. From the decoding maps, all 196 and 225 crystals were clearly identified. The average energy resolutions were 14.1% and 15.6%. For small animal PET systems, the detector ring diameter was 16.5 cm with an axial field of view (AFOV) of 11.8 cm. The simulation data suggests that a reconstructed radial (tangential) spatial resolution of 1.24 (1.25) mm near the center is potentially achievable. For the whole-body human PET systems, the detector ring diameter was 86 cm. The simulation data suggests that a reconstructed radial (tangential) spatial resolution of 3.09(3.38) mm near the center is potentially achievable. From this study we can conclude that the PQS design could achieve high spatial resolutions and excellent energy resolutions on human and animal PET systems with substantially lower production costs and inexpensive readout devices.

I. Introduction

High-Resolution detector blocks have been developed for human and animal PET systems using the photomultiplier-quadrant-sharing (PQS) decoding technology and crystals. Our goal is to develop high-resolution and high-sensitivity PET cameras with lower production costs [1]. In previous work, we demonstrated the decoding capability of the PQS technology with BGO and GSO scintillation detectors [2]–[4]. Due to the fact that have a high optical light yield , a short attenuation length (10.4: 14.1: 11.4, in millimeters), and a short decay time (300: 60: 40, in nanoseconds) [5], it should be possible to develop PQS-PET detectors with better performance than the previous ones. The aim of this study was to test the decoding limits of the lower cost PQS analog decoding technique, to develop high-resolution PQS PET detectors with crystals, to characterize the detector performance, and to estimate the potential PET imaging resolutions that can be achieved with such a detector design, using Monte Carlo simulations.