SPECT reconstruction using preprocessing masking for extra-cardiac uptake versus standard processing in Tc-sestamibi myocardial perfusion imaging.

Objective: In Tc myocardial perfusion SPECT, extra-cardiac accumulation from organs such as the liver or gastrointestinal tract may overlap with the inferior wall, causing artifacts that interfere with image interpretation. This study aimed to quantitatively evaluate the effectiveness of a novel image reconstruction method, the masking process on unsmoothed images (MUS method; CardioMUSk®, PDRadiopharma Inc., Tokyo, Japan), in reducing the influence of extra-cardiac accumulation using both phantom and clinical images.

Methods: This retrospective study included 200 patients (400 scans) who underwent a one-day stress-rest protocol using Tc-sestamibi (MIBI) with pharmacologic stress administered first. Image reconstruction was performed using filtered back projection (FBP) and ordered subset expectation maximization with resolution recovery (OS-EM-RR), both with and without the MUS method. First, visual classification of extra-cardiac accumulation patterns relative to the inferior wall was performed, and the separation capability of each reconstruction method was assessed. Next, phantom experiments were conducted to investigate the effects of extra-cardiac accumulation volume, proximity, and concentration on contrast in the inferior wall. Furthermore, quantitative comparison of relative contrast between the inferior wall and the lateral and septal walls was performed using clinical data.

Results: The MUS method reduced the proportion of visually unseparated cases from 15.5% to 3.5% compared with the conventional method. In phantom studies, larger extra-cardiac accumulation and closer proximity to the myocardium resulted in greater degradation of inferior wall contrast. When a distance of 2 cm was maintained between extra-cardiac accumulation and the myocardium, the effect was substantially reduced. In clinical images, the MUS method significantly improved relative contrast in the inferolateral/inferior wall at the mid-ventricular level (Wilcoxon p = 0.030) and in the inferoseptal/inferior wall at the basal level (Wilcoxon p < 0.001), while no significant improvement was observed in the basal inferolateral/inferior wall region (Wilcoxon p = 0.605).

Conclusion: The MUS method demonstrated enhanced separation of extra-cardiac accumulation and improved contrast in the inferior myocardial wall compared with conventional methods. It was particularly effective in cases where extra-cardiac accumulation overlapped or closely contacted the myocardium, indicating its potential clinical utility in Tc myocardial perfusion SPECT.