Impacts of Acquisition and Reconstruction Parameters on the Absolute Technetium Quantification of the Cadmium-zinc-telluride Based SPECT/CT System: A Phantom Study

BackgroundVarious acquisition and reconstruction parameters may affect the accuracy of the absolute SPECT quantification. However, many of the impacts of these parameters have not well been studied. This study aimed to evaluate the impacts of acquisition parameters (main energy window and acquisition time per frame) and reconstruction parameters (the number of iterations and subsets in iterative reconstruction, post-filter, and image correction methods) on the technetium quantification of the cadmium-zinc-telluride based SPECT/CT system. MethodsA phantom (PET NEMA/IEC image quality, USA) was filled with a 16:1 sphere-to-background activity concentration ratio of technetium and all spheres had 132400.81Bq/ml of radioactivity. Mean uptake values (calculated mean concentrations for spheres) were measured to evaluate the recovery coefficient (RC) changes under different acquisition and reconstruction parameters. Corresponding standard deviations of mean uptake values were also measured to evaluate the quantification error. Image quality was evaluated using the National Electrical Manufacturers Association (NEMA) NU 2-2012 standard.ResultsFor six spheres of the phantom, significant correlations were found between iterations and RCs (r=0.60~0.98 for 1~35 iterations, r=0.96~0.99 for 35~90 iterations, all P-values <0.05) as well as between the full width at half maximum (FWHM) of the Gauss filter and RCs (r=-0.90～-1.00, all P-values <0.05). 1~35 iterations had higher regression coefficients compared with those of 35~90 iterations (0.67~1.16 vs. 0.02~0.17). The AC (attenuation correction)+SC (scatter correction) +RR (resolution recovery correction) combination had more close to 100% RCs (42.42%~98.04%) with better image quality (31.52%~83.57%) than those of other correction combinations (all P-values <0.05). No significant statistical difference was found between the 15% energy window and the 20% energy window (P-value=0.061), nor between the 5 seconds/frame and 120 seconds/frame of acquisition time (P-value=0.943) in terms of RCs. ConclusionsThe CZT-SPECT/CT showed a good quantification accuracy of technetium. The favorable acquisition parameters may be 15% energy window and 40 seconds/frame of acquisition time. The favorable reconstruction parameters could be 35 iterations, 20 subsets, the AC+SC+RR correction combination, and FWHM 0.7mm of Gauss filter.