How shall we judge a PET flow model?

Abstract

Starting over 70 years ago, clinicians began quantifying myocardial blood flow to diagnose and guide treatment. During the past seven decades, a large number of tools has been developed, both invasive and non-invasive. The ongoing utility of myocardial blood flow assessment testifies the underlying clinical need. Why does this patient have chest pain or dyspnea? Should I perform coronary angiography or how should I interpret its anatomy? Will the patient benefit from revascularization? And, if yes, which vessels require a procedure? The ideal tool for studying myocardial blood flow possesses the following features. First, it should be noninvasive to avoid the small, but non-zero, risk of complications inherent to any catheterization and therefore facilitate serial assessment and require small or no radiation exposure. Second, minimal contraindications allow its application to the broadest range of patients regardless of body habitus, heart rate and rhythm, implanted devices, coagulopathy, and renal function. Third, the entire left ventricle must be evaluated independent of the complexity of coronary anatomy, including total occlusions, bypass grafts, and tortuous or calcified vessels. Fourth, since absolute flow depends on the amount of supplied muscle, only normalizing to myocardial mass (= perfusion) permits comparisons among patients, although serial exams in the same patient generally do not require this adjustment. Fifth, the technique should be repeatable with a known and acceptable test/retest variation under stable conditions. Finally, the resolution of the tool must permit distinction among the ‘‘revascularizable’’ vessels (generally at least 2 to 2.5 mm in reference diameter) and quantify their distribution territory as a fraction of the total left ventricle. Since its initial description in animals and humans roughly 40 years ago for myocardial imaging, cardiac positron emission tomography (PET) has matured into the reference standard since it uniquely fulfills all of these ideal features. However, several software packages exist in current practice and, as admitted by a recent national statement on PET blood flow quantification, ‘‘significant variation remains among some vendor programs.’’ The current manuscript by Nesterov et al in this issue therefore provides a timely opportunity to consider how to judge existing PET flow software.