Spatial resolution limits for the isotropic-3D PET detector X’tal cube

Abstract

Positron emission tomography (PET) has become a popular imaging method in metabolism, neuroscience, and molecular imaging. For dedicated human brain and small animal PET scanners, high spatial resolution is needed to visualize small objects. To improve the spatial resolution, we are developing the X’tal cube, which is our new PET detector to achieve isotropic 3D positioning detectability. We have shown that the X’tal cube can achieve 1mm3 uniform crystal identification performance with the Anger-type calculation even at the block edges. We plan to develop the X’tal cube with even smaller 3D grids for sub-millimeter crystal identification. In this work, we investigate spatial resolution of a PET scanner based on the X’tal cube using Monte Carlo simulations for predicting resolution performance in smaller 3D grids. For spatial resolution evaluation, a point source emitting 511keV photons was simulated by GATE for all physical processes involved in emission and interaction of positrons. We simulated two types of animal PET scanners. The first PET scanner had a detector ring 14.6cm in diameter composed of 18 detectors. The second PET scanner had a detector ring 7.8cm in diameter composed of 12 detectors. After the GATE simulations, we converted the interacting 3D position information to digitalized positions for realistic segmented crystals. We simulated several X’tal cubes with cubic crystals from (0.5mm)3 to (2mm)3 in size. Also, for evaluating the effect of DOI resolution, we simulated several X’tal cubes with crystal thickness from (0.5mm)3 to (9mm)3. We showed that sub-millimeter spatial resolution was possible using cubic crystals smaller than (1.0mm)3 even with the assumed physical processes. Also, the weighted average spatial resolutions of both PET scanners with (0.5mm)3 cubic crystals were 0.53mm (14.6cm ring diameter) and 0.48mm (7.8cm ring diameter). For the 7.8cm ring diameter, spatial resolution with 0.5×0.5×1.0mm3 crystals was improved 39% relative to the (1mm)3 cubic crystals. On the other hand, spatial resolution with (0.5mm)3 cubic crystals was improved 47% relative to the (1mm)3 cubic crystals. The X’tal cube promises better spatial resolution for the 3D crystal block with isotropic resolution.