RT Journal Article SR Electronic T1 Accurate single time-point Tc-99m pyrophosphate SPECT imaging at 1h for diagnosis of cardiac transthyretin amyloidosis JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1666 OP 1666 VO 62 IS supplement 1 A1 Khun Visith Keu A1 Joanie Lemay A1 Emilie Vallee YR 2021 UL http://jnm.snmjournals.org/content/62/supplement_1/1666.abstract AB 1666Objectives: Recommendations for the evaluation of cardiac transthyretin amyloidosis (ATTR) rapidly evolve in the past few years. Both planar and single photon emission tomographic (SPECT) image acquisitions at 1h and 3h are usually performed with some variations at different institutions. We believed SPECT imaging only would be sufficient for the diagnosis of ATTR. The purpose of this study was to identify the optimal timing of SPECT image acquisitions and to evaluate the role of planar imaging when SPECT imaging is available. Methods: This retrospective observational study was conducted in one large community hospital. Fifty-two (52) consecutive patients (62% men; median age, 75 [37-94] years) were referred to our department from November 2017 to October 2020. Subjects were injected with 25 ± 1 mCi of Tc-99m pyrophosphate (PYP) with planar images acquired at 66 ± 11 min and 188 ± 15 min. SPECT images were acquired at 78 ± 11 min and 200 ± 18 min. Myocardial PYP uptake was assessed by both visual (grading comparison of myocardial to rib uptake) and semi-quantitative (heart-to-contralateral lung uptake ratio, H:CL) methods as recommended by ASNC. An H:CL ≥ 1.5 was classified as positive and a ratio of < 1.5 as negative. A grade 2-3 on either planar or SPECT imaging was considered positive for ATTR and a grade 0-1 as negative. Two independent observers reassessed all the scans without reviewing the electronic medical charts or previous exams. Upon disagreement between the observers, a third observer would review the case for a final decision. The correlations between different imaging protocols were compared and discordances (positive versus negative for ATTR) were noted. Our findings were then compared to the dictated report and correlated to the clinical follow-up. Results: There was a strong correlation between 1h and 3h planar H:CL ratio (mean difference 0.06, r = 0.92) with only 3/52 (6%) discordance. However, the grading approach for planar images at 1h and 3h demonstrated 8/52 (15%) discordance. The comparison between planar and SPECT images at 1h and 3h demonstrated respectively 6/52 (12%) and 2/52 (4%) discordance. For almost all discordant cases, the persistent blood pool activity at 1h overestimated the uptake in the heart region. In two (2) cases, the overlying activity from the ribs falsely increased the uptake on planar imaging. SPECT images performed at 1h and 3h showed identical results for diagnosis of ATTR with 11/52 (21%) considered positive. Using only the H:CL ratio at 1h or 3h, 4/52 (8%) would be misdiagnosed and 7/52 (13%), if the grading approach in planar imaging was used. Of all imaging protocols, SPECT at 1h or 3h correlated the most with the dictated report and the clinical follow-up. Conclusions: This study demonstrated that SPECT imaging alone at 1h is accurate for the diagnosis of ATTR. A single delay SPECT imaging at 3h is also a valid alternative. Planar images may be omitted since they are more susceptible to artefacts related to blood pool and the overlap of bone uptake. However, our findings need further validation in a multicenter trial.