Dual-ended readout small animal PET detector by using 0.5 mm pixelated LYSO crystal arrays and SiPMs

Abstract

Small animal PET scanners need to have a high spatial resolution since the size of the organs of small animals is much smaller than that of humans, and also need to have a high sensitivity since the allowed injection dose is limited by the radiation dosimetry of the small organs. To simultaneously achieve high spatial resolution and high sensitivity for a small animal PET scanner, detectors with high position resolution, high efficiency and high depth of interaction (DOI) resolution are required. In this work, three 17×17 pixelated LYSO arrays with crystal size of ∼0.5 mm and an outer dimension of 10×10×20mm3 are fabricated. The first LYSO array uses 80μm thick BaSO4 reflector. The second and the third LYSO arrays use 65μm thick Toray reflectors. The outermost side of the third LYSO array is also wrapped with k9 glass of the same size as the crystals in the array in order to improve the light collection and flood histogram quality for the edge crystals. The LYSO arrays are read out with two Hamamatsu SiPM arrays from both ends. The SiPM array is 4×4, with 3×3mm2 pixel size and 0.2 mm gap in between the SiPM pixels. The SiPM array is read out with a resistor network circuit to reduce the number of signals from 16 to 4. The performance of the detector in terms of flood histograms, energy resolution, DOI resolution and timing resolution was measured. All three detectors provide good flood histograms and all crystals in an array can be clearly resolved. The average DOI resolutions of individual crystals are 1.84, 1.98 and 1.93 mm for the three detectors for events with energy E > 350 keV. The BaSO4 array has higher light output and provides a better average crystal energy resolution of 21.0 %. The photopeak amplitude of the Toray arrays changes with depth, which results in worse energy resolutions of 24.4 % and 23.8 % for the two detectors respectively. The average timing resolutions of individual crystals are 1.23, 1.27 and 1.24 ns for the three detectors for events with E > 350 keV. All three detector modules achieved high position resolution (0.5 mm crystal size), high efficiency (20 mm crystal length) and high DOI resolution (<2.0 mm) and can be used to build a high sensitivity small animal PET scanner with spatial resolution approaching the physical limit.