Optimization of dual-layer phoswich detector for small animal positron emission tomography (PET)

Abstract

As an effective imaging probe in the area of animal models of human disease, gene expression and therapy, and drug discovery and development, small animal PET imaging is being used increasingly. An ideal small animal PET should have a high sensitivity and uniform resolution across the field of view to achieve high image quality. Dual-layer scintillators, so called phoswich detectors, for small animal PET have been developed to measure the depth of interaction and to improve resolution performances. The aim of this study was to optimize the length, order and adhesion condition of the dual layer phoswich detector to achieve high image quality and a high count rate of small PET. The sensitivity and resolution of a small PET scanner was estimated by Monte Carlo simulation. The proposed scanner is based on dual layer phoswich detector modules arranged in a ring of 10 cm diameter. Each module is composed of 8 x 8 arrays of phoswich detectors consisting of LSO and LuYAP with a 2 mm x 2 mm sensitive area coupled to a 64-channel PMT. The length of the front layer of phoswich detector was varied from 0 to 10 mm at 1 mm intervals, and the total length (LSO + LuYAP) was fixed at 20 mm. The order of the crystal layers of phoswich detector was also changed. Radial resolutions were kept below 3.4 mm and 3.7 mm over 8 cm FOV, and sensitivities were 7.4% and 8.0% for LSO 5 mm-LuYAP 15 mm, and LuYAP 6 mm-LSO 14 mm phoswich detectors, respectively. Whereas, high and uniform resolutions were achieved by using LSO as a front layer scintillator, higher sensitivities were obtained by changing the crystal order. Simple analytic forms to calculate the optimal length of the phoswich detector were derived by analyzing the most obliquely incident event. For various combinations of front and back layer materials of the phoswich detector, lengths of front layers, which can minimize the effect of depth of interaction on the broadening of the spatial resolution, were estimated and were valida...