INTEROBSERVER AND INTERSTUDY VARIABILITY OF MYOCARDIAL BLOOD-FLOW ANDFLOW-RESERVE MEASUREMENTS WITH NITROGEN 13 AMMONIA-LABELED POSITRON EMISSION TOMOGRAPHY

Background. Experimental studies have shown that positron emission tom ography (PET) with N-13-labeled ammonia provides accurate quantificati on of regional myocardial blood flow (MBF) under rest and stress condi tions, To establish the clinical utility of this method, the interobse rver variability and the temporal variability of serial measurements o f blood flow and coronary flow reserve (CFR) must be known. This study investigated the interobserver and temporal reproducibility of N-13-l abeled PET for measurement of MBF and CFR. Methods and Results. Initia l and follow-up N-13-labeled ammonia PET studies were performed at res t and during adenosine infusion in six normal volunteers and six patie nts with stable coronary artery disease. Two investigators analyzed dy namically acquired data from the initial studies and one investigator analyzed the follow-up studies. Time-activity curves of tissue tracer activity were derived by a semiautomated sampling routine. A three-com partment model and curve-fitting algorithm were used to determine esti mates of MBF in five myocardial regions. The interobserver correlation s for MBF and CFR were excellent (r = 0.96 and 0.93, respectively). Th e interstudy correlation was good for rest and stress MBF (r = 0.87). The estimates of CFR on the initial and follow-up studies demonstrated a fair correlation (r = 0.72). For individual myocardial regions, the re was considerable interstudy variability of stress MBF and CFR, with a mean percent difference for CFR of 19% +/- 19% in normal volunteers and 38% +/- 16% in patients with coronary disease. In normal subjects , regional CFR was highly reproducible (95%) when the values were defi ned as either normal (greater than or equal to 2.5) or reduced (< 2.5) . Conclusions. The interobserver of reproducibility of N-13-labeled am monia PET estimates of regional MBF was excellent. The temporal reprod ucibility of MBF and CFR was fair, with individual regions demonstrati ng substantial interstudy variability.