A continuous depth encoding PET detector using side readout of dual-layer GAGG crystals with SiPM array

Abstract

A continuous depth encoding positron emission tomography (PET) detector using a side readout configuration with dual-layer GAGG scintillators of different decay times, coupled to a Silicon Photomultiplier (SiPM) array is proposed. The performance of the detector was evaluated through experimentation. The detector consists of an upper layer with a 1 × 4 fast decay GAGG (GAGG-F) crystal array and a lower layer with another 1 × 4 high-light-yield GAGG (GAGG-HL) crystal array. The 2 × 4 GAGG crystal array is then coupled to the 4 × 6 SiPM array. The SiPM array's sum signal is utilized for layer identification, while 24 individual signals are used to measure the 3D position of the gamma interaction. The experimental measurements demonstrate that the detector effectively resolves all crystal units and provides continuous depth information in the Z-direction. Utilizing the time over threshold method for dual-layer identification in coincidence mode yielded an accuracy of 96.4 %, whereas the pulse decay time method achieved an accuracy of 95.7 %. The average energy resolution was found to be 12.1 % and 11.2 % for the upper and lower GAGG crystal arrays, respectively. Using the maximum value-to-sum ratio method, the upper GAGG-F crystal layer displayed clear distinction and accurate assignment at two height positions, achieving a correct assignment rate of 90.5 %. In contrast, the lower GAGG-HL crystal layer exhibited poorer resolution at each height position, with correct assignment percentages dropping to 71.1 %. Employing the center of gravity position estimation method for the GAGG-F and GAGG-HL layers, the average Z spatial resolution was determined as 3.56 ± 0.33 mm (FWHM) and 3.35 ± 0.28 mm (FWHM).