Phantom evaluation of dynamic SPECT imaging with a ring-type semiconductor SPECT/CT system: comparison with an anger-type system

Abstract Purpose The introduction of ring-type semiconductor single-photon emission computed tomography (SPECT)/computed tomography (CT) systems has generated growing interest in the clinical application of dynamic SPECT imaging. Nevertheless, the efficacy of dynamic SPECT in clinical practice has not yet been sufficiently demonstrated. This study assessed the imaging characteristics of dynamic SPECT using a ring-type semiconductor SPECT/CT system (ring-type system) through phantom experiments and determined the optimal parameters for image reconstruction and Becquerel calibration factors (BCFs). Methods Two 40-mL balloon tubes were placed at the central and periphery of a cylindrical phantom. A Tc-99m solution was infused at a constant rate using a syringe pump to simulate dynamic changes in radioactivity over time. Dynamic SPECT imaging was performed using a ring-type system, and dynamic planar imaging was also performed using an Anger-type system for comparison. Radioactivity concentrations in the balloons were measured during dynamic imaging to generate time–activity curves (TACs). Dynamic SPECT data were reconstructed using acquisition times of 5 and 15 s and eight different values of β (the noise suppression parameter in the Bayesian penalty likelihood method): 0.005–0.2. The validity of the quantitative evaluation was examined, including the necessity of specific conversion factors for radioactivity concentration. The optimal reconstruction parameters for dynamic SPECT were explored by comparing the TACs obtained from the two systems. Results The TACs obtained from planar imaging demonstrated superior linearity compared to those obtained from SPECT. The TACs in SPECT tended to show significant variability, particularly during short acquisition times. In contrast, when two adjacent balloons overlapped, planar imaging produced a merged curve, whereas SPECT resolved them separately. A comparison of images at various β values revealed that under low-count-rate conditions, high β values (0.12–0.2) resulted in excessive noise suppression and signal loss. Regarding the BCF used to calculate the radioactivity concentration from the reconstructed images, its value was highly dependent on the acquisition and reconstruction conditions. The results closest to the theoretical values were obtained under conditions with a β value of 0.02. Conclusion The TACs obtained using a ring-type system in dynamic SPECT demonstrated reduced linearity and greater fluctuations than those acquired with an Anger-type system. We successfully demonstrated that dynamic SPECT enables accurate separation and measurement of targets even when two adjacent targets overlap in planar images. We also identified image reconstruction parameters and BCFs that are appropriate for dynamic SPECT.