CT 減弱補正におけるSPECT 画像とX 線CT 画像の位置ずれが骨SPECT の定量性に与える影響

Purpose: 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. Methods: 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. Results: 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. Conclusions: 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.