Design Study of the DOI-PET Scanners with the X\u27tal Cubes Toward Sub-Millimeter Spatial Resolution

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 PET resolution, we are developing X\u27tal cube, which is our new PET detector to achieve isotropic 3D positioning detectability. It consists of a segmented 3D crystal block of which all surfaces are covered with semiconductor photo-sensors. We have shown that the X\u27tal cube can achieve (1 mm)3 uniform crystal identification performance. To improve further spatial resolution, we intend to develop the sub-millimeter X\u27tal cube. However, one problem that prevents its commercial mass production is handling the small crystal pieces, i.e., cutting out and assembling them. In this work, to evaluate to benefit of the sub-millimeter X\u27tal cube, we simulated dedicated brain and small animal PET scanners with X\u27tal cubes using a Monte Carlo simulation and calculated spatial resolutions with the X\u27tal cubes with from (0.5 mm)3 to (1.0 mm)3 cubic crystals. For spatial resolution evaluation, a point source emitting 511 keV photons was simulated with all physical processes involved during emission and interaction of positrons. The brain PET scanner has a detector ring of 275 mm in diameter composed of 48 detectors. The small animal PET scanner has a detector ring of 82 mm in diameter composed of 14 detectors. The simulated data were projected to the sinogram and reconstructed using the 2D filtered backprojection. For the small animal PET scanner, we showed that sub-millimeter spatial resolution is possible using the X\u27tal cube with cubic crystals smaller than 0.9 mm even with the physical processes. On the other hand, for the brain PET scanner, spatial resolutions increased 20% larger than these of the small animal PET scanner due to the non-collinearity effect. However, for both PET scanners, we showed that the spatial resolution significantly improved, as cubic crystals were smaller