New articles published: V. 14 n. 2 (2026)

Monte Carlo simulations study of non-collinear gamma-ray cascade correlation emissions for medical imaging

Abstract: Conventional imaging techniques such as SPECT and PET cannot directly identify the positions of individual decaying nuclei. As such, they heavily rely on statistical backprojection for image point reconstruction. Therefore, this study explores an alternative approach using non-collinear gamma-ray cascade emissions, which are emitted directly from the decay position and unaffected by positron movement. Detecting these cascades in coincidence allows precise localization of decay events, enabling direct image point reconstruction. To evaluate this concept, GATE Monte Carlo simulation was used to simulate the cascade emission from ¹¹¹In-ion point sources and detection using collimated small animal PET scanner. Finally, a custom image reconstruction algorithm was developed to estimate the three-dimensional position of a decaying nucleus by calculating the midpoint of the shortest segment, or the intersection, between two collimator projections from a valid coincidence event. The results show that at the center of the field of view, image sensitivities of 22.2 cps/MBq in air and 20.0 cps/MBq in a PMMA phantom were achieved. Furthermore, a spatial resolution of 4.1 mm FWHM was obtained in the transaxial direction and 7.6 mm FWHM in the axial direction. The imaging system is capable of resolving two-point sources separated by 8.0 mm (transaxial) and 10.0 mm (axial). The results from this simulation study indicate that the proposed imager with its image reconstruction method surpasses conventional PET and SPECT in emission point localization accuracy. Read full article.