Effect of depth of interaction resolution on the performance of SIAT aPET

Depth encoding detectors are required to simultaneously achieve high sensitivity and uniform high spatial resolution for small animal PET scanners. As compared to other depth encoding PET detectors, dual-ended readout detectors can achieve much higher depth of interaction (DOI) resolution. In this work, the effects of DOI resolution on the spatial resolution of SIAT aPET that has a 111 mm detector ring diameter and uses crystals of 1x1x20 mm³ were investigated by imaging a point source and a Derenzo phantom. The detectors of SIAT aPET achieved a DOI resolution of ~2 mm. The DOI information of the list-mode data were rebinned to 1, 2, 4, 8, and 16 DOI bins to simulate different DOI resolutions of the detectors. The images were reconstructed by using an ordered subsets expectation maximization (OSEM) algorithm with point spread function (PSF) modeling using spatial variant PSF parameters. First, the spatial resolution was evaluated by using a Na-22 point source placed at center axial field of view (FOV) with different radial offsets. Then, the imaging resolution of the scanner was evaluated by using a Derenzo phantom placed at the center and 15 mm off radial center FOV. The radial spatial resolution at large radial offsets were significantly affected and the axial spatial resolution was also moderately affected by the DOI effect if the DOI was not measured. A number of DOI bins of 8 or more was required to achieve a uniform high spatial resolution in the center 60 mm FOV for the SIAT aPET scanner.