A Monte Carlo study on quantification of scattering and edge penetration in a breast-dedicated SPECT scanner with lofthole collimation

Introduction: Quantitative accuracy in SPECT is mainly affected by collimator penetration and scattering, particularly for high-energy imaging. Lofthole collimation offers superior performance in terms of penetration and scattering.Methods: In this research, the GATE Monte Carlo simulator was exploited to calculate edge penetration and scattering in the lofthole collimator using an in-air and in-phantom point source of Tc-۹۹m and I-۱۲۳. The performance of the lofthole was then compared to that of a pinhole. Both lofthole and pinhole collimators were assumed to have the same geometry including an aperture diameter of ۳.۰۴ mm and an opening angle of ۷۵°. Furthermore, the angular distribution of the scattering and penetration were investigated for a multi-lofthole collimator.Results: The results show that penetration, scattering, and sensitivity are all a function of the photon energy. The penetration and scattering of the pinhole are about ۴% higher than that of the lofthole collimator, for Tc-۹۹m SPECT. Compared to the Tc-۹۹m, I-۱۲۳ SPECT suffers from approximately ۱.۵- and ۱.۴۲-fold higher penetration and scatter fractions, respectively, for lofthole aperture. Moreover, the lofthole collimator presents a higher sensitivity compared with the pinhole (۰.۰۳۰ versus ۰.۰۲۳ for the Tc-۹۹m SPECT). In addition, the findings exhibit a reduction in sensitivity by increasing the photon incidence angle. Both scattering and penetration fractions illustrate a decreasing trend across the angle of incidence.Conclusion: Compared to pinhole, the lofthole offers superior performance in terms of scattering and penetration for both low- and high-energy SPECT imaging.

کلیدواژه ها:

Penetration ، Scattering ، SPECT ، Collimator ، Monte Carlo Simulation ، Lofthole