Cardiac viability PET using combined parametric 15O-water blood flow/18F-FDG metabolism compares well with 82Rb/18F-FDG

1632 Introduction: Myocardial viability in patients with ischemic heart failure (iHF) can be assessed using combined 18F-FDG and perfusion PET scans. The extent and severity of scarring and perfusion/metabolism hibernation (mismatch) is commonly quantified using differences between normalized 18F-FDG and normalized perfusion tracer-retention polar maps as suggested in the PARR-1 study (1). However, since perfusion tracer-retention depends on both tracer extraction and wash-out, quantification and useful pathology cut-offs depend on the tracer used. The original PARR-1 and PARR-2 studies were performed using either 82Rb or 13N-ammonia retention radiotracers. Both are radiotracers, which exhibit significant retention signal roll off at higher flows. This is contrary to parametric images of transmural myocardial blood flow (tMBF) measured by 15O-water PET, which accurately reflects myocardial blood flow even at high flow. In this study, we apply the PARR-1 methodology to calculate mismatch (hibernation) and scar scores from 15O-water PET parametric images (tMBF/FDG) and compare it to standard retention images with low extraction (82Rb/FDG). Methods: 12 iHF patients referred for viability assessment were studied using all three radiotracers on the same day (the perfusion tracers 15O-water and 82Rb and the metabolism tracer 18F-FDG). Using the aQuant Research SW package, the left ventricle was segmented and images of retention (82Rb) and parametric images of tMBF (15O-water) were produced. Perfusion and FDG-images were fused, and normalized perfusion, metabolism, scar, and mismatch polar maps were calculated according to the PARR algorithm. Furthermore, tMBF images were subjected to a reverse 82Rb extracting correction (2) to produce retention equivalent images from 15O-water (retenEq). Differences were analyzed using Blandt-Altman plots with log transformation where appropriate. Results: Mismatch score was three times higher for tMBF/FDG compared to 82Rb/FDG (median 11% [4-36] vs 4% [1-14], p