A novel preclinical system for cascade gamma photon coincidence imaging with high resolution and sensitivity

We present a novel high-resolution, high-sensitivity time-space coincidence imaging system for cascade gamma photons. The system employs a LaBr 3 ring detector with hybrid pinhole-slit collimators, combining the high spatial resolution of pinhole collimation with the high detection efficiency of slit collimation. Simulations were conducted with a point source and a Derenzo phantom using 177 Lu, a theranostic radionuclide that emits cascade gamma-ray pairs at 113 keV and 208 keV. Images were reconstructed using direct back-projection (DBP) and maximum likelihood expectation maximization (MLEM), as well as two newly proposed algorithms: refined DBP (R-DBP) and multi-information joint reconstruction (MIJR).The system achieved a central coincidence efficiency of 2.98×10⁻⁵. Point source imaging with MLEM reconstruction yielded a spatial resolution of 1.7 mm full width at half maximum (FWHM) in the transaxial plane. Derenzo phantom imaging demonstrated clear resolution of hot rods as small as 1.2 mm in diameter, with a contrast-to-noise ratio (CNR) of 9.29 for the largest rods.These results demonstrate that the proposed ring detector enables high-quality cascade gamma photon coincidence imaging, with spatial resolution and sensitivity that significantly exceed those of previously reported systems. The combination of high resolution, reasonable sensitivity, and theranostic capability positions this technology as a promising platform for integrated diagnosis and therapy.