Optimization of number of iterations as a reconstruction parameter in bone SPECT imaging using a novel thoracic spine phantom

Abstract

Objective: The aim of this study was to optimize of the number of iterations in bone single-photon emission computed tomography (SPECT) imaging using a novel thoracic spine phantom (ISMM phantom). Methods: The quality and quantitative accuracy of bone SPECT images were evaluated by changing the number of iterations and the size of the hot spot in the phantom. The phantom image was reconstructed using the order subset expectation maximization (OSEM) algorithm with Computed tomography-based attenuation correction, scatter correction, and resolution recovery; the number of OSEM subsets was fixed at 10, with iterations ranging from 1 to 40. Full width at half maximum (FWHM), percent coefficient of variation (%CV), contrast ratio for the sphere and background (contrast) and recovery coefficient (RC) were evaluated as a function of the number of iterations for a given number of subsets (10) using the reconstructed images. In addition, the maximum, peak, and mean standardized uptake values (SUV_max, SUVpeak, and SUVmean) were calculated with various numbers of the iterations for each sphere (13, 17, 22, and 28 mm) simulating a tumor. Results: FWHM decreased with an increasing number of iterations and converged uniformly when the number of iterations was over 10. %CV increased with an increasing number of iterations. RC was decreased with a decreasing size of sphere. Contrast and all SUVs increased with an increasing number of iterations and converged uniformly when the number of iterations was over 5 and 10 in all sphere sizes, respectively. The SUVmean with 10 iterations was 55.9, 26.6, 14.9, and 9.9 at 28 mm, 22 mm, 17 mm, and 13 mm, respectively. The relative error in the converged values for SUV_max, SUVpeak, and SUVmean were 43.8%, 27.3%, and 7.2% of the true value (52.2); all the SUVs were overestimated. Conclusion: Using a thoracic spine phantom to evaluate the optimal reconstruction parameter in bone SPECT imaging, the optimal number of iterations for a given number of subsets (10) was determined to be 10.