Evaluation of the performance of parallel-hole collimator for high resolution small animal SPECT: A Monte Carlo study

Introduction: Image quality and accuracy of in vivo activity quantification in SPECT are affected by collimator penetration and scatter components, especially in high energy imaging. These phenomena highly depend on the collimator characteristic and photon energy. The presence of penetrated and scattered photons from collimator in SPECT images degrades spatial resolution, contrast and image quality. Knowledge of penetration and scatter distribution is essential for optimization of collimator design and development of reconstruction algorithms.The aim of this study to survey the collimator performance of the newly developed HiReSPECT dual head gamma camera with pixelated array CsI(Na). Methods:We modeled the HiReSPECT, by using SIMIND Monte Carlo simulation code. The contribution of geometric, scatter and penetration components were quantitatively calculated for the different energy sources. Then we compared these results with simulation results of another small animal SPECT with compact pixelated array CsI(Tl) detector. Results:The simulated System spatial resolution and energy resolution of the HiReSPECT at 140keV respectively are 1.9mm and 29.72 keV (21.23%) FWHM  at 2.5cm distance from detector surface also Geometric, penetration, and scatter at 140keV for the HiReSPECT collimator are 96.42%, 2.22%, 1.30%, respectively. Similarly, geometric, penetration, and scatter at 159keV and 245keV for this system collimator are (95.24%, 3.08%, 1.68%) and (87.21%, 8.10%, 4.69%), respectively. Conclusion: The results verified that the magnitude of these components depend on collimator geometric structure and photons energy. The measured performances indicated that the HiReSPECT scanner is well suited for preclinical molecular imaging research and provide high resolution for small animal imaging.