Optimization of pinhole aperture size of a combined MPH/fanbeam SPECT system for I-123 DAT imaging

We proposed an inexpensive method to improve the performance of the conventional dual-camera SPECT systems for I-123 dopamine transporter (DAT) imaging for Parkinson Disease. In this method, one of the collimators is replaced with a specifically designed multi-pinhole (MPH) collimator, thus performing combined MPH/Fanbeam acquisition. The MPH consists of 9 pinholes focusing to the central brain and covering a cylindrical field of view (diameter: 12cm and height: 8cm), which includes the striatum. We present here our Monte Carlo simulation work investigating the optimal aperture size for the striatal binding ratio (SBR) and caudate/putamen ratio (C/P). Projections of the XCAT brain phantom were obtained for a range of aperture sizes (radius:1-5 mm, with increments of 1mm). Multiple noise realizations were simulated for each aperture size at realistic count levels. Reconstructions from MPH, Fanbeam and combined MPH/Fanbeam systems were obtained for various numbers of iterations. For SBR and C/P calculations activities within the striatum were estimated for a range of region of interests. Normalized root mean square errors (NRMSE) of the SBR and C/P measurements were obtained for the Fanbeam and combined MPH/Fanbeam reconstructions at different iterations and VOIs, using custom made and clinically employed quantitative analysis software. Our preliminary results suggest that an aperture radius of 2-3 mm for the MPH component yields both visually and quantitatively better estimations for the MPH/Fanbeam reconstructions.