Sensitivity and spatial resolution simulation of a PET-compton insert imaging system

Abstract

PET is the most sensitive imaging technique in the field of nuclear medicine. However, the single count rate is typically 10 times higher than the coincidence count rate. This means that there are a lot of pairs of undetected annihilation photons. For single gamma imaging, Compton imaging is known as the only method to obtain directional information of an incoming gamma ray without using collimators. Compton kinematics collimation suffers from poor angular resolution due to Doppler broadening, energy blurring, and position blurring. Therefore, Compton imaging is still challenging compared to PET imaging in general. However, non-coincidence single photons have the potential to contribute to improved imaging performance. Previously, we have proposed a system which combines PET and Compton imaging and we showed high sensitivity of this system using Compton kinematics collimation events. In this paper, we evaluate sensitivity and spatial resolution for feasibility of this system. This system modeled the PET ring and the inserted Compton scatter ring. The PET ring consisted of 48 DOI detectors arranged in five rings with a ring diameter of 80 cm. The PET ring was made of GAGG with a size of 2.9 × 2.9 × 5 mm3 including 4-layered DOI capability. Ring diameters of the scatter ring were selected as 30, 40, 50 and 60 cm. Detector material of the scatter ring was Si with a pixel size of 0.9 × 0.9 × 0.6 mm3. From point source measurements, images of PET and Compton events were individually reconstructed by the 3D-LM-OSEM algorithm. From point source measurements at the center of the field-of-view, spatial resolution with 30 cm diameter was 3 mm. Also, as the position of the point source was close to the detector, spatial resolution was improved. The proposed system had a potential of high spatial resolution for not only PET imaging but also Compton imaging with the small scatter ring.