H²RSPET: a 0.5 mm resolution high-sensitivity small-animal PET scanner, a simulation study

Abstract

With the goal of developing a total-body small-animal PET system with a high spatial resolution of ∼0.5 mm and a high sensitivity >10% for mouse/rat studies, we simulated four scanners using the graphical processing unit-based Monte Carlo simulation package (gPET) and compared their performance in terms of spatial resolution and sensitivity. We also investigated the effect of depth-of-interaction (DOI) resolution on the spatial resolution. All the scanners are built upon 128 DOI encoding dual-ended readout detectors with lutetium yttrium oxyorthosilicate (LYSO) arrays arranged in 8 detector rings. The solid angle coverages of the four scanners are all ∼0.85 steradians. Each LYSO element has a cross-section of 0.44 × 0.44 mm2 and the pitch size of the LYSO arrays are all 0.5 mm. The four scanners can be divided into two groups: (1) H2RS110-C10 and H2RS110-C20 with 40 × 40 LYSO arrays, a ring diameter of 110 mm and axial length of 167 mm, and (2) H2RS160-C10 and H2RS160-C20 with 60 × 60 LYSO arrays, a diameter of 160 mm and axial length of 254 mm. C10 and C20 denote the crystal thickness of 10 and 20 mm, respectively. The simulation results show that all scanners have a spatial resolution better than 0.5 mm at the center of the field-of-view (FOV). The radial resolution strongly depends on the DOI resolution and radial offset, but not the axial resolution and tangential resolution. Comparing the C10 and C20 designs, the former provides better resolution, especially at positions away from the center of the FOV, whereas the latter has 2× higher sensitivity (∼10% versus ∼20%). This simulation study provides evidence that the 110 mm systems are a good choice for total-body mouse studies at a lower cost, whereas the 160 mm systems are suited for both total-body mouse and rat studies.

Ultra‐high‐resolution depth‐encoding small animal PET detectors: Using GAGG and LYSO crystal arrays

“…Zhang et al 40 optimized a high-resolution PET detector with a LYSO crystal of 0.5 × 0.5 × 6.25 mm 3 size and performed initial image studies with a prototype PET scanner consisting of 12 optimized detectors. However, for all the prototype small animal PET scanners developed so far with spatial resolution approaching 0.5 mm, the sensitivity was still much lower than current commercial small animal PET scanners.Lai et al 41 performed Monte Carlo simulations to design small animal PET scanners that can achieve ∼0.5 mm spatial resolution and high sensitivity with different scanner geometries and crystal lengths.…”

“…However, for all the prototype small animal PET scanners developed so far with spatial resolution approaching 0.5 mm, the sensitivity was still much lower than current commercial small animal PET scanners. Lai et al 41 . performed Monte Carlo simulations to design small animal PET scanners that can achieve ∼0.5 mm spatial resolution and high sensitivity with different scanner geometries and crystal lengths.…”

Technical opportunities and challenges in developing total-body PET scanners for mice and rats

“…5 Total-body small animal PET scanners need to have an axial length longer than the length of the mice/rats to maximize sensitivity across the entire body of the animals. The PET scanner (H 2 RS110) shown in this figure, which is designed for total-body mouse studies only, has a 110 mm ring diameter and 167 mm axial length [ 12 ] …”

“…Groups from the University of California at Davis and the University of Texas Arlington have proposed a design to build a scanner with a 110 mm ring diameter and 167 mm axial length for total-body mouse studies (Fig. 5 ) [ 12 ]. This scanner is based on dual-ended readout detectors based on position-sensitive SiPMs (PS-SiPMs) coupled to both ends of 20 mm thick LYSO arrays (H 2 RS110 shown in Figs.…”

“…This scanner is based on dual-ended readout detectors based on position-sensitive SiPMs (PS-SiPMs) coupled to both ends of 20 mm thick LYSO arrays (H 2 RS110 shown in Figs. 1 , 2 , 3 ) [ 12 , 51 , 52 ]. Besides increasing the sensitivity, LYSO arrays of 0.44 × 0.44 × 20 mm 3 crystal elements (0.5 mm pitch size) are used to achieve the physical limits of spatial resolution that could be obtained from coincidence detection.…”