Evaluation of Optimal Ordered Subset Expectation Maximization Reconstruction for [I-123]FP-CIT Single-Photon Emission Computed Tomography Using a Ring-Type Semiconductor Scanner

A recently introduced ring-type single-photon emission computed tomography (SPECT)/computed tomography (CT) scanner equipped with 12 small semiconductor detectors is expected to shorten the acquisition time and improve spatial resolution. This study evaluated the optimal ordered subset expectation maximization (OSEM) reconstruction for [I-123] N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodo-phenyl) nor tropane SPECT using a striatum phantom. The phantom was filled with an I-123 solution, and the radioactivity concentration ratio in the background, right striatum, left caudate, and left putamen was 1:8:8:4. The evaluated acquisition time was 15, 20, 30, and 120 min. The acquired data were reconstructed using OSEM under various conditions. The reconstructed images were evaluated regarding coefficient of variation (Δ%CV), normalized mean squared errors (NMSE), and visual interpretation. In addition, the striatal uptake ratio (SUR) and contrast ratio of the images were compared between the ring-type and the conventional 2-detecter (Anger-type) scanner. The Δ%CV of the 120 min image was sufficiently small when the number of updates reached 100 and converged uniformly. The NMSE of the 20 and 30 min images were almost constant when the number of updates exceeded 120. Regarding visual interpretation, cut-off frequencies of 0.4 and 0.5 cycles/cm for the Butterworth filter were considered optimal. The SUR and contrast ratio of the ring-type scanner were significantly higher than those of the Anger-type. In conclusion, an acquisition time of 20 min, OSEM reconstruction with 120 updates, and a Butterworth filter of 0.4-0.5 cycles/cm were suitable for [I-123]FP-CIT SPECT using a ring-type scanner.