Dynamic Acquisition of [^99mTc]Tc-Pyrophosphate SPECT/CT Images in Transthyretin Cardiac Amyloidosis: A Pilot Study

The objectives of this study were to determine the timing of peak [^99mTc]Tc-pyrophosphate uptake in the myocardium, blood pool, and bone and to explore the feasibility and advantage of early imaging compared with the standard late imaging in participants with and without transthyretin amyloid cardiomyopathy (ATTR-CM). Methods: Dynamic [^99mTc]Tc-pyrophosphate SPECT/CT data were acquired at 0-5 min and 10-65 min, with additional 15-min static scans at 90 and 150 min using a full-ring cadmium zinc telluride scanner. Image analysis included visual assessment and established quantitative metrics that require calibrated SPECT images, such as SUV_mean and SUV_max and percentage injected dose per milliliter, along with relative uptake ratios (myocardium to bone and myocardium to blood pool) that do not require calibration. ATTR-CM and non-ATTR-CM cohorts were compared. Results: Our study included 19 participants: 8 with ATTR-CM (median age of 80 y with an interquartile range of 9.3 y) and 11 (57.9%) without ATTR-CM. In ATTR-CM, SUV_mean was significantly higher in the myocardium than in the blood pool at 10 min (3.86 ± 0.77 vs. 3.08 ± 0.58, P = 0.0055). Myocardial SUV_mean remained elevated over time, with a statistically significant decline from 3.86 ± 0.77 at 10 min to 2.88 ± 0.57 at 150 min (P = 0.0025). In patients without ATTR-CM, myocardial SUV_mean remain relatively stable across all time points (1.24 ± 0.41 at 10 min to 0.94 ± 0.21 at 150 min, P = not statistically significant). In both groups, bone SUV_mean peaked at 90 min, and the blood pool showed the highest SUV at 10 min, followed by a decrease through 150 min. Percentage injected dose per milliliter clearly separated the ATTR-CM from the non-ATTR-CM groups at all time points. Conclusion: In participants with ATTR-CM, myocardial uptake peaked by 10 min after injection and remained stable, with minimal washout, through 150 min; non-ATTR-CM participants showed consistently lower myocardial uptake than blood pool uptake at all time points. These findings suggest that early imaging can perform as well as late imaging for diagnosis of ATTR-CM, supporting the potential of early imaging to streamline patient care.