High-Resolution GAGG-SiPM Detectors for Preclinical Coincidence SPECT

Coincidence detection of cascade decay in single photon emission computed tomography (SPECT) can enhance image quality by detecting true events and rejecting uncorrelated scatter. This study presents the development of high-resolution detectors based on 24 × 24 gadolinium aluminum gallium garnet (GAGG) arrays with a 1.0 mm pitch and 8 × 8 silicon photomultiplier (SiPM) arrays with a 3.2 mm pitch, which were designed for preclinical coincidence SPECT applications. Compton scatter events from annihilation photons were employed to mimic cascade photons and to evaluate the timing performance of the detectors. Moreover, the performance of the detectors with and without using 1 mm thick clear acrylic sheets as light guides was compared. Flood histograms showed that all GAGG elements were clearly identified except a small number of edge crystals when events with energies in a 100 - 250 keV energy window were used, and the use of the light guide improved crystal identification. The detectors with light guides achieved coincidence timing resolutions of 678 ± 143 ps, 571 ± 118 ps, and 374 ± 74 ps with events in 100 - 250 keV, 100 - 450 keV, and 400 - 650 keV energy windows, respectively. The corresponding values provided by detectors without the light guide were 551 ± 135 ps, 458 ± 114 ps, and 314 ± 68 ps. Energy resolutions at 511 keV were 9.2 ± 0.7% and 11.0 ± 0.7% for detectors with and without the light guide, respectively. These results demonstrated that the developed GAGG-SiPM detector with the light guide was a suitable candidate for developing preclinical coincidence SPECT systems.