From the Turku PET Centre (S.K., H.T.S., M.T., J.K.), Department of Medicine (E.J., M.P., H.U., A.S., J.A.), and Department of Clinical Physiology and Nuclear Medicine (M.S., M.M., J.H.), University of Turku, Turku, Finland.
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Background—The standard interpretation of perfusion imaging is based on the assessment of relative perfusion distribution. The limitations of that approach have been recognized in patients with multivessel disease and endothelial dysfunction. To date, however, no large clinical studies have investigated the value of measuring quantitative blood flow and compared that with relative uptake.Methods and Results—One hundred four patients with moderate (30%–70%) pretest likelihood of coronary artery disease (CAD) underwent PET imaging during adenosine stress using 15O-water and dynamic imaging. Absolute myocardial blood flow was calculated from which both standard relative myocardial perfusion images and images scaled to a known absolute scale were produced. The patients and the regions then were classified as normal or abnormal and compared against the reference of conventional angiography with fractional flow reserve. In patient-based analysis, the positive predictive value, negative predictive value, and accuracy of absolute perfusion in the detection of any obstructive CAD were 86%, 97%, and 92%, respectively, with absolute quantification. The corresponding values with relative analysis were 61%, 83%, and 73%, respectively. In region-based analysis, the receiver operating characteristic curves confirmed that the absolute quantification was superior to relative assessment. In particular, the specificity and positive predictive value were low using just relative differences in flow. Only 9 of 24 patients with 3-vessel disease were correctly assessed using relative analysis.Conclusions—The measurement of myocardial blood flow in absolute terms has a significant impact on the interpretation of myocardial perfusion. As expected, multivessel disease is more accurately detected.Clinical Trial Registration—URL: http://www.clinicaltrials.gov. Unique identifier: NCT00627172.