Optimization of a High Resolution Small Animal SPECT System using GATE and STIR Software

Single photon emission computed tomography (SPECT) has been widely used for preclinical research. High resolution small animal SPECT imaging can be achieved by employing a pinhole or multi-pinhole collimators. However, the useful FOV is narrow compared to that of a parallel-hole collimator. The aim of this study is to optimize the hole diameter of a parallel square-hole collimator for high resolution wholebody small animal SPECT imaging using GATE and STIR software. The small animal SPECT consists of a tungsten parallel square-hole collimator (L= 30 mm), a monolithic GAGG crystal (49 × 49 × 5 mm3), and a PMT (H9500). The SPECT images of an Ultra-Micro hot phantom and NEMA NU-4 phantom were acquired with different square-hole sizes of 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mm. The collimator length and septal thickness were kept as 30 mm and 0.1 mm, respectively. The projection image (128 × 128 matrix, pixel size of 0.3828 × 0.3828 mm2) was reconstructed with FBP, and OSMAPOSL algorithms provided by STIR software. With the collimator hole size of 0.4 mm, the spatial resolution of 1.11 mm and sensitivity of 0.001% could be achieved. The contrast recovery coefficient could be improved by using the 0.4 mm hole size and the hot rods (D= 1.35 mm) could be identified clearly. The important message from this work is that the small animal SPECT system can be optimized with the open-source software packages of GATE and STIR. In the future, a prototype small animal SPECT will be developed based on the GATE simulation results