Effect of Misregistration between SPECT and CT Images on Attenuation Correction for Quantitative Bone SPECT Imaging

Abstract

The aim of this study was to evaluate the effect of misregistration between single-photon emission computed tomography (SPECT) and computed tomography (CT) images on bone SPECT. We acquired SPECT and CT images of a body phantom filled with bone-equivalent solution and 99mTc for evaluation of bone SPECT. SPECT images were reconstructed using attenuation correction maps obtained by shifting the attenuation coefficients from non-shifted values (reference). Activity concentrations, SPECT standardized uptake values (SPECT-SUVs), and tumor background ratios (TBRs) were evaluated. Activity concentrations and SPECT-SUVs decreased with decreasing attenuation coefficient. The difference in attenuation coefficient was especially large between the shifted-to-lung (0.085 cm-1) and reference (0.249 cm-1) values. Non-shifted and shifted-to-lung SPECT-SUVs were 11.5±1.0 and 2.3±0.2, respectively. TBR also decreased with decreasing attenuation coefficient. The maximum percentage change in TBR was 86% in the shifted-to-lung value. Our results indicate that the accuracy of activity concentration and lesion detectability was commonly affected by misalignment between SPECT and CT images. Although the impact of SPECT/CT misregistration on bone SPECT is case-specific and difficult to predict, it is important to reduce the incidence of misregistration errors for quantitative bone SPECT imaging.