Myocardial perfusion imaging (MPI) has a well-established role in diagnosis, risk stratification and prognostication in patients with suspected or known coronary artery disease (CAD)(1,2). As the current health-care landscape moves towards rewarding value, there is an increased urgency for determining the role of imaging tests in improving patient-centered outcomes (3-5). Traditionally, the cardiac imaging community has focused on studying "hard outcomes" such as cardiac morbidity and mortality, with relatively little attention on patient-centered health status outcomes (e.g. symptoms, function and quality of life).

While Single Photon Emission Computed Tomography (SPECT) has been a myocardial perfusion imaging (MPI) mainstay for decades, use of Positron Emission Tomography (PET) MPI has been increasing as it offers superior spatial resolution, lower radiation exposure, higher diagnostic accuracy, shorter acquisition times and quantification of myocardial blood flow reserve (MBFR) (6-9). MBFR integrates the hemodynamic effects of microvascular dysfunction, diffuse atherosclerotic disease and epicardial stenosis on myocardial tissue perfusion, and as such is more likely to correlate with patient's anginal symptoms, functional status and quality of life (10,11). MBFR measured by PET MPI has been shown to provide independent and incremental prognostic value for major adverse cardiac events beyond perfusion defect analysis, but has not been evaluated for its association with symptoms, function and quality of life (although in a post-hoc analysis of 171 patients with known CAD undergoing PET MPI enrolled in the ASPIRE study at our center, higher MBFR was significantly associated with lower anginal burden as measured by the Seattle Angina Questionnaire (SAQ; unpublished data, being presented at ASNC 2018)) (8,10,12-15). Among 329 patients, Taqueti et al demonstrated that patients with low global MBFR were less likely to require subsequent heart failure hospitalizations and cardiac deaths if treated with early revascularization with bypass surgery, but not percutaneous coronary intervention (PCI), as compared with medical management; however the low number of events and the small sample size were major limiting factors (10). More recently, among 12,594 patients undergoing PET MPI, we demonstrated that MBFR \<1.8 may help identify patients with a survival benefit from early revascularization within 90 days of the index MPI test. (unpublished data, being presented at AHA 2018). In a sub-study of the PACIFIC study, Driessen et al showed strong correlation of change in MBFR post revascularization with change in FFR; providing further support for non-invasively measured MBFR as a potential measure to target intervention, similar to FFR, which needs invasive measurement on coronary angiography (16).

To further elucidate the mechanism of action by which MBFR could be used to target management for ischemic heart disease, we propose a study of serial PET MPI in 75 patients undergoing coronary stenting to evaluate the association of changes in MBFR with changes in patients' health status. About a quarter to half of stable CAD patients treated with PCI continue to have angina and poor quality of life after stenting (17-19) This may be because stenting is only directed at epicardial stenoses, while many patients have concomitant microvascular disease. While there has been some data where serial PET MPI studies have been used to look at changes in perfusion defect sizes and flows with anti-ischemic medications and statins (20-24) it is not known whether these changes are associated with improved outcomes. We propose to perform PET MPI studies in patients before and after stenting to evaluate changes (or lack thereof) in MBFR and how that is associated with changes (or lack thereof) in symptoms, functional status and quality of life. This will help to understand the role of MBFR in patient selection for coronary angiography and stenting.