Influence of the Number of Detector Rings on the Count Rate Performance of a 32-Ring PET and a 96-Ring PET: A Monte Carlo Simulation Study

Abstract

Background: Most clinical whole-body PET scanners are full ring scintillation detection systems with an axial field of view (AFOV) ranging from 15 to 22 cm. A full ring scintillation detection system is often composed with 32, 64, or 96 detector rings. Long AFOV scanners with covered large solid angles will catch more true coincidence, random, and scatter events. Building up a real 96 detector ring PET system is a complex project, and not financially practicable. Modern Monte Carlo tools can aid in assessing and overcoming these deficiencies. The purpose of this study is to evaluate the influence of 32 detector rings and 96 detector rings on a PET scanner in terms of its count rate performance by Monte Carlo simulation. Material and Methods: All of the Monte Carlo simulations are performed using version 6.2 of the Geant4 Application for Tomographic Emission (GATE), which is based on GEANT4 version 9.5. The 32-ring virtual PET scanner is made of four rings of BGO blocks that have been partially cut into an 8 × 8 array of crystals that measure 4 × 4 × 30 mm each, resulting in an 82.7 cm diameter detector cylinder and an axial field of view (FOV) length of 15.5 cm. The 96-ring PET was simulated with the same parameter settings as the 32-ring PET, but the block ring repeater parameter was changed from 4 to 12. All count rate performance and sensitivity tests were arranged follow the NEMA NU2-2001 protocol. Results: The scanner sensitivity of the 32-ring PET was 7.05 cps/kBq (R = 0 cm) and 7.63 cps/kBq (R = 10 cm). The scanner sensitivity of the 96-ring PET was 63.23 cps/ kBq (R = 0 cm) and 68.91 cps/kBq (R = 10 cm). The system sensitivity of the 96-ring PET was almost 9 times higher than that of the 32-ring PET. The scatter fractions of the 32-ring PET and the 96-ring PET were 48.02% and 53.12%. The simulated peak NECR_(1R) were 21.79 kcps @ 6.82 kBq/c.c. and 122.23 kcps @ 4.09 kBq/c.c. with the 32-ring PET and the 96-ring PET.