Quantification of regional myocardial perfusion by PET: rationale and first clinical results

With the recent advances in interventional cardiology there is increasing need for characterization of the functional effects of coronary artery stenosis. Stress echocardiography and SPECT perfusion imaging are standard techniques for the qualitative assessment of regional function and perfusion in patients with proven or suspected coronary artery disease. However, Positron emission tomography (PET) provides quantitative measurements of regional myocardial perfusion. In combination with pharmacological stress testing, relative and absolute coronary reserve measurements can be used to define functional significance of regional coronary artery disease. First clinical results indicate that there is an overall agreement between angiographic and functional disease severity. However, there is a relatively large scatter of coronary reserve flow in patients with 50-90% coronary artery stenosis, which emphasizes the complimentary role of perfusion imaging in the prediction of functional severity. In addition, first studies in asymptomatic patients with a high risk for coronary artery disease suggest that PET coronary reserve flow measurement may be more sensitive than angiographic criteria for detection of early alterations in coronary vascular reactivity. Absolute quantification of blood flow may be useful in disease processes which affect the entire left ventricle such as vasculopathy in cardiac transplants, as well as endothelial dysfunction in patients with hypertension and cardiomyopathy. Future studies have to demonstrate the prognostic value of the quantitative estimate of coronary reserve as regards clinical outcome in patients with various coronary abnormalities. Quantitative flow measurements will be useful for monitoring progression and regression of coronary artery disease as well as assessment of acute and chronic therapy.