Effects of acquisition mode and arm position on myocardial perfusion imaging with a full-ring semiconductor SPECT/CT: ECG-gated myocardial phantom study

Abstract Purpose The full-ring semiconductor SPECT/CT systems utilize a focus mode to enhance image quality and reduce acquisition time. However, the impact of arm positioning on this mode remains under-investigated. This study evaluated the effects on image quality during electrocardiography-gated myocardial perfusion SPECT acquisition under different imaging modes. Methods We used an electrocardiography-gated myocardial phantom with the Tc-99 m solution adjusted to simulate myocardial concentration. The upper limb portion of the whole-body phantom was attached to simulate the arms-down position and removed to simulate the arms-up position. Acquisitions were performed in both the arms-up and arms-down positions using two imaging modes: a uniform mode covering the body contour and a focus mode targeting the heart. Contrast analysis, polar map assessment, and cardiac functional analysis were performed and compared across different conditions. Results Under all conditions, the number of myocardial counts was higher in Uniform Mode than in Focus Mode; however, the number of ventricular cavity counts was significantly reduced in Focus Mode. When using CTAC, the mean myocardial count in Focus Mode was 11,075 ± 1064 (arms raised) and 9467 ± 843 (arms lowered), whereas the ventricular cavity counts were minimized to 261 ± 191 and 631 ± 318, respectively. As a result, Focus Mode consistently achieved superior contrast ratios, recording a maximum value of 0.98 ± 0.03 in the arm-raised position using CTAC + SC. Polar map analysis revealed that focus mode improved myocardial uniformity and mitigated uptake reductions in the septal and lateral walls compared to uniform mode, particularly under the arms-down condition. Quantitative gated SPECT (QGS) showed that while EDV was underestimated across all modes, focus mode provided EF values (27.7 [range:27.6–27.8] % for arms-down, 27.1 [range: 25.7–28.5] % for arms-up), closely matching the theoretical value of 27.7%. In contrast, uniform mode significantly overestimated EF, particularly in the arms-down condition (35.4 [range: 33.1–37.7]%). Conclusions Focus mode acquisition with arms-up represents the optimal imaging approach for maximizing image contrast and facilitating reliable assessment of cardiac functional parameters in full-ring semiconductor SPECT/CT systems. Furthermore, focus mode maintains similar quantitative accuracy even when imaging is performed with the arms-down, thereby enabling relatively high level of evaluation in patients with limited physical mobility and enhancing its clinical utility.