Design of a combined fan and multi-pinhole collimator combination for clinical I-123 DaTscan imaging on dual-headed SPECT systems

For the recently FDA approved Parkinson´s Disease (PD) SPECT imaging agent I-123 labeled DaTscan the volume of interest (VOl) is the interior portion of the brain. However imaging of the occipital lobe is also required with PD for calculation of the striatal binding ratio (SBR), a parameter of significance in early diagnosis, differentiation of PD from other disorders with similar clinical presentations, and monitoring progression. Thus we propose the usage of a combination of a multi-pinhole (MPH) collimator on one head of the SPECT system and a fan-beam on the other. The MPH would be designed to provide high resolution and sensitivity imaging of the interior portion of the brain. The fan-beam collimator would provide lower resolution but complete sampling of the brain addressing data sufficiency and allowing a volume-of-interest to be defined over the occipital lobe for calculation of SBR´s. Herein we analyze 20 clinical DaTscan studies to provide information on the VOl, and then design a MPH collimator to image this VOl. Using standard collimator equations we determine a system spatial resolution for the MPH of 4.4 mm which is comparable to that of clinical PET systems, and significantly smaller than that of fan-beam collimators employed in SPECT. The combined sensitivity of the apertures of the MPH was larger than that of an ultra-high resolution fan-beam (LEUHRF) collimator, but smaller than that of a high resolution fan-beam collimator (LEHRF). On the basis of these early results we propose the exploration of further improvements in design, and the development of combined MPH and fan-beam reconstruction.