Optimization of Block Sequential Regularized Expectation Maximization Reconstruction Parameters for Striatal SPECT Using a Ring-Type Semiconductor SPECT/CT System.

Abstract

This phantom study aimed to optimize the noise-suppression parameter (β) and the edge-preservation parameter (γ) values in the block sequential regularized expectation maximization (BSREM) reconstruction method for ¹²³I-2-β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl)nortropane striatal SPECT using a ring-type cadmium-zinc-telluride camera. Methods: We used a striatum phantom filled with an ¹²³I solution, with adjusted concentrations in the left and right caudate and left and right putamen. The phantom was scanned for 120 min using the StarGuide system, and 20-min SPECT data were extracted from the total acquisition. Using the BSREM method, we generated 42 reconstructed images by varying β and γ. We calculated the percent coefficient of variation and percent contrast for each image. Visual evaluations were conducted by a nuclear medicine physician and 2 technologists. Additionally, we calculated the striatal uptake ratio (SUR) and the ratio of the left caudate SUR to putamen SUR in the left striatum (left striatal ratio). Results: The percent coefficient of variation decreased as the β value increased, whereas percent contrast increased as the γ value increased. We conducted a visual evaluation of 15 reconstructed images selected by physical assessment. Images reconstructed with a β value of 0.03 with a γ value of 5 and those with a β value of 0.05 with a γ value of 10 were deemed suitable for diagnostic purposes because of their accurate depiction of tracer accumulation in each striatal region. SUR and left striatal ratio were comparable for these 2 image sets. Conclusion: Evaluation of the optimal conditions for striatal SPECT imaging with BSREM reconstruction revealed that the optimal β value and γ value combinations were a β value of 0.03 and γ value of 5 and a β value of 0.05 and γ value of 10.