Evaluation of a Sub-Millimeter Resolution PET Detector With a 1.2 mm Pitch TSV-MPPC Array One-to-One Coupled to LFS Scintillator Crystals and Inter-Crystal Scatter Studies With Individual Signal Readout

Abstract

To develop a small animal positron emission tomography (PET) scanner for whole body imaging of mice, a sub-millimeter resolution PET detector has been constructed and its performance evaluated. This PET detector is composed of a 1.2 mm pitch multi-pixel photon counter (MPPC) $ {8\times 8}$ array with through-silicon via (TSV) structure one-to-one coupled to Lutetium Fine Silicate (LFS) scintillator crystals of size 1.13 mm $ {\times \,\,1.13}$ mm $ {\times \,\,10}$ mm each. To evaluate the intrinsic spatial resolution and the energy resolution in coincidence events, the coincidence response functions (CRFs) of the detector pair, located facing each other at a distance of 80 mm, were measured by scanning a 0.25 mm diameter 22Na point source in 0.1 mm steps. The data were acquired by the computer automated measurement and control (CAMAC) system. The average full width at half maximum (FWHM) of the CRFs was 0.75 mm without point source size corrections. The average FWHM of the energy resolution was 16% at 511 keV. The coincidence timing resolution (CTR) was also evaluated by facing the detector and a fast photomultiplier tube (PMT) coupled with a BaF2 crystal. The expected average FWHM of the CTR between the detectors was 770 ps. Additionally, to improve detector efficiency while suppressing the positioning errors, we propose an interaction-order scheme based on Compton kinematics and adapt it to the same data. We also perform Monte Carlo simulations using GEANT4 10.01 to evaluate the accuracy of the proposed positioning scheme and compare it to that of a centroid calculation scheme. As a result, we demonstrate that the accuracy of the proposed positioning scheme is better than that of a centroid calculation scheme when inter-crystal scatter events occur.