Abstract
Positron emission tomography/computed tomography (PET/CT) applied with positron-emitting flow tracers such as 13N-ammonia and 82Rubidium enables the quantification of both myocardial perfusion and myocardial blood flow (MBF) in milliliters per gram per minute for coronary artery disease (CAD) detection and characterization. The detection of a regional myocardial perfusion defect during vasomotor stress commonly identifies the culprit lesion or most severe epicardial narrowing, whereas adding regional hyperemic MBFs, myocardial flow reserve (MFR), and/or longitudinal flow decrease may also signify less severe but flow-limiting stenosis in multivessel CAD. The addition of regional hyperemic flow parameters, therefore, may afford a comprehensive identification and characterization of flow-limiting effects of multivessel CAD. The non-specific origin of decreases in hyperemic MBFs and MFR, however, prompts an evaluation and interpretation of regional flow in the appropriate context with the presence of obstructive CAD. Conversely, initial results of the assessment of a longitudinal hyperemic flow gradient suggest this novel flow parameter to be specifically related to increases in CAD caused epicardial resistance. The concurrent assessment of myocardial perfusion and several hyperemic flow parameters with PET/CT may indeed open novel avenues of precision medicine to guide coronary revascularization procedures that may potentially lead to a further improvement in cardiovascular outcomes in CAD patients.
Highlights
Positron emission tomography/computed tomography (PET/CT)-guided assessment of myocardial perfusion with concurrent quantification of myocardial blood flow (MBF) in milliliters per gram per minute by means of radiotracer kinetic modeling affords a comprehensive identification and delineation of subclinical and clinically manifest coronary atherosclerosis [1,2,3,4,5,6]
Cardiac PET imaging with short-lived positronemitting flow tracers injected intravenously, like 13N-ammonia, 82Rubidium, or 15O-water, and dynamic image acquisition of the radiotracer traversing through the pulmonary arterial system to its extraction and retention in the left ventricle (LV) affords the quantification of regional MBF in milliliter per gram per minute during vasomotor stress, at rest, and its myocardial flow reserve (MFR) (MFR = hyperemic MBF/rest MBF)
Operational equations are used in order to compensate for physical decay of the radiotracer, partial volumecaused underestimation of the true myocardial tissue concentration, and spillover of radioactivity between right- and left ventricular blood pool and the myocardium. Such a non-invasive approach with PET to quantify MBF in milliliters per gram per minute has been validated for 13N-ammonia, 82Rubidium, or 15O-water against independent microsphere blood flow assessment at rest and during pharmacologically induced hyperemia [30,31,32,33,34,35]
Summary
Positron emission tomography/computed tomography (PET/CT)-guided assessment of myocardial perfusion with concurrent quantification of myocardial blood flow (MBF) in milliliters per gram per minute by means of radiotracer kinetic modeling affords a comprehensive identification and delineation of subclinical and clinically manifest coronary atherosclerosis [1,2,3,4,5,6]. In patients with established CAD, the unraveling of a regional myocardial perfusion defect during pharmacologically stimulated hyperemic flows signifies the most severe epicardial narrowing, while less severe but flow-limiting stenosis in multivessel CAD can be identified through reductions in hyperemic flow, MFR, and the longitudinal flow gradient [1, 5, 6, 24,25,26] Such a diagnostic approach, incorporating several hyperemic flow parameters into the evaluation, may enable a comprehensive detection of downstream effects of “each” CAD lesion on hyperemic flow in multivessel disease. The aim of this article is to discuss the potential role of the combined assessment of myocardial perfusion and MBF by PET/CT in the identification and delineation of multivessel CAD in the clinical routine
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