Advantage of Pinhole Collimators Over Parallel Hole Collimators in Reducing Downscatter for I-123 Imaging

Previously, we proposed an inexpensive method to improve the performance of the existing general-purpose dual-camera SPECT systems for brain imaging with I-123 (DaTscan) by using a specifically designed multi-pinhole (MPH) collimator on one of the detector heads. We present here our preliminary work investigating the downscatter of the low-abundance high-energy photons of I-123 for our MPH collimator in comparison to a single-pinhole and a parallel-hole collimator. These investigations were conducted with GATE Monte Carlo simulations and validated with experimental studies on a Philips Prism2000 SPECT system (1.905 cm crystal) for which we have single-pinhole and parallel-hole collimators. The downscatter fractions (DSF) obtained from the Prism2000 experiments were 26.8% for the parallel-hole (LEUHR) and 3.4% for the single-pinhole collimators, which are similar to the simulation results: 26.3% for the LEUHR and 4.2% for the single-pinhole. DSF for the MPH (0.9525 cm crystal) was only 1.5% because of the large tungsten collimator plate. These quantitative results are in good agreement with the energy spectra obtained from the simulations and real acquisitions. Thus, our study shows that an additional benefit of using pinhole systems is the negligible downscatter for I-123 brain imaging.