Search

The purpose of this study was to determine the inter- and intra-observer variability in 99mtechnetium-pyrophosphate (99mTc-PYP) scan interpretation for diagnosis of transthyretin cardiac amyloidosis (ATTR). Our study cohort comprised 100 consecutive subjects referred for 99mTc-PYP imaging based on clinical suspicion of ATTR cardiac amyloidosis. Myocardial 99mTc-PYP uptake was assessed by both visual (comparison of myocardial to rib uptake) and semi-quantitative (heart-to-contralateral lung uptake ratio, H:CL) methods. Twenty scans were analyzed twice, at least 48 hours apart, by each of two independent observers. Patients with visual scores of ≥ 2 on planar imaging as well as myocardial uptake on SPECT/CT were classified as ATTR positive. Diagnosis of ATTR by visual 99mTc-PYP grade was perfectly reproducible [concordance: positive and negative scans 100% (53/53 and 47/47, respectively). Both inter- and intra-observer correlations for H:CL ratio (r2 = 0.90, 0.99 (Observer 1) and 0.98 (Observer 2), respectively) and repeatability values on Bland–Altman plots were excellent. The coefficient of variation (%) for Observers 1 and 2 was 3.21 (2.14 to 4.29) and 7.49 (4.95 to 10.09), respectively. In addition, there was 100% concordance in positive and negative scan interpretation by visual grading between novice CV imagers (< 3 years’ experience) and an experienced CV imager (10 years’ experience). This study showed excellent inter-observer reproducibility and intra-observer repeatability of 99mTc-PYP visual scan interpretation and H:CL ratio for diagnosis of cardiac ATTR amyloidosis. Cardiac ATTR amyloidosis can be diagnosed reliably using 99mTc-PYP SPECT/CT by novice and experienced CV imagers.

The clinical diagnosis of pulmonary involvement in individuals with systemic AL amyloidosis remains challenging. [18F]florbetapir imaging has previously identified AL amyloid deposits in the heart and extra-cardiac organs. The aim of this study is to determine quantitative [18F]florbetapir pulmonary kinetics to identify pulmonary involvement in individuals with systemic AL amyloidosis. We prospectively enrolled 58 subjects with biopsy-proven AL amyloidosis and 9 control subjects (5 without amyloidosis and 4 with ATTR cardiac amyloidosis). Pulmonary [18F]florbetapir uptake was evaluated visually and quantified as distribution volume of specific binding (Vs) derived from compartmental analysis and simpler semiquantitative metrics of maximum standardized uptake values (SUVmax), retention index (RI), and target-to-blood ratio (TBR). On visual analysis, pulmonary tracer uptake was absent in most AL subjects (40/58, 69%); 12% (7/58) of AL subjects demonstrated intense bilateral homogeneous tracer uptake. In this group, compared to the control group, Vs (median Vs 30-fold higher, 9.79 vs. 0.26, p 3-fold higher Vs compared to the control group (median 0.99 vs. 0.26, p < 0.001). Vs was independently related to left ventricular SUVmax, a marker of cardiac AL deposition, but not to ejection fraction, a marker of cardiac dysfunction. Also, intense [18F]florbetapir lung uptake was not related to [11C]acetate lung uptake, suggesting that intense [18F]florbetapir lung uptake represents AL amyloidosis rather than heart failure. [18F]florbetapir PET/CT offers the potential to noninvasively identify pulmonary AL amyloidosis, and its clinical relevance warrants further study.