Reproducibility and Repeatability of Assessment of Myocardial Light Chain Amyloidosis Burden Using ¹⁸F-Florbetapir PET/CT

Background: ¹⁸F-florbetapir PET is emerging as an excellent quantitative tool to quantify cardiac light chain (AL) amyloidosis burden. The primary aim of this study was to determine interobserver reproducibility and intraobserver repeatability, defined per the recommendations of the Quantitative Imaging Biomarker Alliance technical performance group, of PET ¹⁸F-florbetapir retention index (RI) in patients with cardiac AL amyloidosis. Methods: The study cohort comprised 37 subjects with systemic AL amyloidosis enrolled in the prospective study: Molecular Imaging of Primary Amyloid Cardiomyopathy (clinical trials.gov NCT: 02641145). Using 10 mCi of ¹⁸F-florbetapir, a 60-minute dynamic cardiac scan was acquired. Global and segmental left ventricular estimates of retention index (RI) of ¹⁸F-florbetapir were calculated (Carimas 2.9 software, Turku, Finland). RI was analyzed twice, at least 24 hours apart, by two independent observers. Intraobserver repeatability and interobserver reproducibility were evaluated using Bland–Altman plots and scatter plots with fitted linear regression curves. Results: All reproducibility (interobserver, r = 0.98) and repeatability (intraobserver, R=0.99 for each observer) measures of ¹⁸F-florbetapir RI are excellent. On the Bland–Altman plots, the agreement limits for global ¹⁸F-florbetapir RI were high and ranged for reproducibility (interobserver) from − 9.3 to + 9.4% (Fig. 1), and for repeatability (observer 1 from − 10.8 to + 10.7% and from − 9.2 to + 11.4%, for observer 2). Conclusions: The present study showed excellent interobserver reproducibility and intraobserver repeatability of ¹⁸F-florbetapir PET retention index in patients with cardiac AL amyloidosis.