Feasibility of adjustable-gantry PET system using advanced DOI method

Abstract

Small-animal positron emission tomography (PET) systems are useful functional imaging systems for pathology and pharmacology research. However, conventional small-animal PET systems show degradation with regard to spatial resolution and sensitivity when small objects are image with a scanner having large diameter. In this study, to overcome this limitation, we propose a small-animal PET using an adjustable gantry and a depth-of-interaction (DOI) detector. The adjustable gantry allows the field of view (FOV) to be changed depending on object size to increase the solid-angle coverage and improve sensitivity. In addition, detector modules are arranged in a square shape to fill gaps between the detector module as well as in the corners to achieve higher sensitivity. To overcome the parallax error that occurs in the square-shaped gantry with long and thin crystal elements, a DOI detector is employed using a depth-dependent reflector pattern. The adjustable-gantry PET (AGPET) system is designed by GATE Monte Carlo simulation and evaluated by comparison with conventional small-animal PET systems, such as Inveon and PETbox, in terms of spatial resolution and sensitivity. The DOI detector blocks were composed of two 8 × 8 SiPM arrays coupled to two blocks of 12 × 12 lutetium-yttrium oxyorthosilicate (LYSO) crystals of size 2.1 ×2.1× 20 mm3. The signals of the detector blocks are fed to a data acquisition system based on field-programmable gate array, and the position, energy, and time information were recorded. The detector module performance is analyzed by the peak-to-valley ratio (PVR), distance-to-width ratio (DWR), energy resolution, and timing resolution. The results demonstrate that the proposed AGPET potentially provide higher sensitivity and resolution for small animal imaging.