Regional SPECT imaging using sampling Principles and Multiple Pinholes

There may be many SPECT imaging applications in which a small region is primarily of interest. One such case is imaging in the radiation therapy treatment room, as the patient is on the treatment table in position for radiation therapy. This onboard imaging is currently performed by cone-beam CT. The purpose of this onboard imaging is to fine tune localization of the tumor target. It has been proposed that onboard SPECT could be useful for target localization and also for imaging biological function for the purpose of real-time re-planning of therapy beams. Onboard imaging would need to be accomplished within about 5 minutes. Herein we propose that this might be done by regional SPECT imaging in which multi-pinhole collimation is used to concentrate a large detector surface on a small (e.g. 7cm-diameter) region. Pinhole trajectories are designed in accord with recent developments regarding complete sampling in the presence of truncation. A 9-pinhole system is found to outperform two single-pinhole systems as well as a smaller, reference parallel-hole-collimated detector. Realistic computer-aided design (CAD) studies are shown to illustrate how an onboard SPECT system could be implemented.