Recent years have seen remarkable advances in nuclear cardiology. The introduction of cardiac positron emission tomography (PET) and the development of cadmium-zinc-telluride (CZT) imaging systems have significantly improved diagnostic accuracy, clinical decision-making, and ultimately outcomes for patients with coronary artery disease (CAD). In this issue, Giubbini and Milan review key concepts related to myocardial ischemia and explore the emerging importance of quantifying coronary flow reserve (CFR) in patients with known or suspected CAD.

PET imaging has become a preeminent modality in the evaluation of ischemic heart disease, providing high diagnostic and prognostic value. PET imaging offers several advantages over other imaging modalities, including low radiation exposure, accurate assessment of left ventricular function and perfusion, and the ability to quantitatively measure myocardial blood flow (MBF) and CFR. CFR is defined as the ratio of exercise MBF to resting MBF and reflects not only obstructive CAD but also diffuse atherosclerosis and microvascular dysfunction (CMD) throughout the coronary system. The ability to measure absolute flow and flow reserve is particularly beneficial in cases of multivessel disease or CMD, complementing traditional perfusion imaging, as both conditions can occur even when perfusion appears normal.

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