Cascade Gamma Photon Coincidence Imaging System: a Simulation Study

Cascade radiation refers to radiation from a decaying nuclide via a transition from high to low energy levels occurring in a very short time and producing two or more gamma photons with specific energies. In this article, we proposed a novel idea to develop a time-space coincidence imaging system with high resolution and high sensitivity for using cascade gamma photons. The proposed idea was studied on a simulated system for cascade gamma photon imaging using Monte Carlo simulation via GATE software. We designed a ring detector made of LaBr3 material, with pinhole-slit collimation which combines the high spatial resolution of pinhole collimation and the high detection efficiency of slit collimation. We simulated a point ¹⁷⁷Lu source in the center field of view (CFOV). Then we reconstructed the image and evaluated the potential of determining the position of the decaying nuclide from the temporal and spatial coincidence of cascade gamma photon pairs. The center hole slit efficiency (8581 counts) is 2.49×10^-5, and the center point random coincidence efficiency (1027 counts) is 12.0% of the effective events. The Full Width at Half Maximum (FWHM) resolution is about 1.7 mm. The FWHM in the X direction is 1.69 mm, the FWHM in the Y direction is 1.85 mm, and the FWHM in the Z direction is 2.25 mm. The experimental results show that the cascade gamma photon coincidence imaging ring detector system can produce good-quality images. It is a promising technique for cascade gamma photon coincidence imaging and has great potential in the integration of diagnosis and treatment.