A thick semi-monolithic scintillator detector for clinical PET scanner.

Both monolithic and semi-monolithic scintillator PET detectors can measure the depth of interaction with single-ended readout. Usually scintillators with a thickness of 10 mm or less are used since the position resolutions of the detectors degrade as the scintillator thickness increases. In this work, the performance of a 20 mm thick long rectangular semi-monolithic scintillator PET detector was measured by using both single-ended and dual-ended readouts with SiPM arrays to provide a high detection efficiency. The semi-monolithic scintillator detector consists of 9 LYSO slices measuring 1.37×51.2×20 mm3 with ESR foils of 0.065 mm thick in between the slices. The SiPM array at each end of the scintillator detector consists of 16×4 SiPMs with a pixel size of 3.0×3.0 mm2 and a pitch of 3.2 mm. The 64 signals of each SiPM array are processed by using the TOFPET2 ASIC individually. All but the edge slices can be clearly resolved for the detectors with both single-ended and dual-ended readouts. The single-ended readout detector provides an average full width at half maximum (FWHM) Y (continuous direction) position resolution of 2.43 mm, Z (depth direction) position resolution of 4.77 mm, energy resolution of 25.7% and timing resolution of 779 ps. The dual-ended readout detector significantly improves the Y and Z position resolutions, slightly improve the energy and timing resolution at the cost of two photodetectors required for one detector module and provides an average FWHM Y position resolution of 1.97 mm, Z position resolution of 2.60 mm, energy resolution of 21.7% and timing resolution of 718 ps. The energy and timing resolution of the semi-monolithic scintillator detector of this work are worse than those of the segmented scintillator array detector and need to be further improved. The semi-monolithic scintillator detector of this work reduces the cost of detector as compared to the traditional segmented scintillator array detector and reduces the edge effect as compared to the monolithic scintillator detector.