Adaptation of a Brain-Dedicated Multipinhole SPECT System for Imaging Higher-Energy Photons of Theranostic Agents—A Simulation Study

Multi-pinhole SPECT of the brain is capable of producing high-resolution images. However, pinhole imaging of high-energy photons remains challenging due to the trade-off of greatly sacrificing sensitivity to limit penetration through the edges of the pinholes and system shielding. The impact of photon penetration on spatial resolution, image contrast, and lesion signal-to-noise was assessed through simulation for the brain-dedicated multi-pinhole system AdaptiSPECT-C. In addition, minor changes to the system design to reduce penetration were considered; these were updating the materials of the pinhole aperture edges and shutters to a higher-density tungsten alloy and including platinum in the shielding around the pinhole apertures. A significant degradation in spatial resolution, image contrast, and signal-to-noise above approximately 200 keV was found with the current system design. It was shown that adapting the pinhole and shutter material to a higher-density tungsten alloy would greatly reduce this degradation and permit multi-pinhole imaging with 177Lu and 111In in the human brain. Incorporating a small amount of platinum around each aperture further improved the system point-spread function. However, results indicate high-resolution imaging of 131I would require a larger modification to the system design.