Magnetic resonance measurement of coronary blood flow

Magnetic resonance (MR) flow measurement in the coronary artery can be achieved with either a breath‐hold acquisition or a respiration‐triggered acquisition. MR measurements of cardiac output are significantly depressed during breath‐holding at deep inspiration, but the advantage is that the breath‐hold method requires less scan time. Blood flow in the coronary sinus reflects the global myocardial blood flow because it represents approximately 96% of the total myocardial blood flow of the left ventricle (LV). If blood flow in the coronary sinus is measured with phase‐contrast cine magnetic resonance imaging (MRI) and LV myocardial mass is measured with cine MRI, both the total myocardial blood flow and the average coronary blood flow per gram of myocardial mass can be quantified. Coronary flow reserve with volumetric MR flow measurement is measured to be within 4.2–5.0‐fold. The noninvasive MR measurement of coronary flow reserve has been shown to be useful in identifying the functional significance of stenoses in the left anterior descending artery. The sensitivity and specificity of MR coronary flow velocity reserve for identifying stenosis of 70% or greater in the left main or left anterior descending artery were 100% and 83%, respectively. The MR quantification of total coronary blood flow and coronary blood flow per gram of myocardial mass seems to be an ideal method for evaluating coronary hemodynamics and may be useful in evaluating endothelial dysfunction of the coronary circulation.SummaryRecent advances in fast MRI sequences have considerably extended the capabilities of cardiac MRI in the functional assessment of coronary blood flow and flow reserve. The MR measurement of coronary flow reserve can be used to identify restenosis of the left main and left anterior descending coronary arteries after percutaneous interventions in clinical patients. Further refinements in MR pulse sequences, including the use of phase‐contrast echo‐planar or spiral MR methods, may make it possible to quantify blood flow volume and flow reserve more accurately in all major branches of the coronary arteries.The MR measurement of blood flow through the coronary sinus allows a noninvasive assessment of global coronary hemodynamics. Because the coronary sinus is larger than the native coronary arteries, the errors in blood flow quantification associated with the limited spatial and temporal resolution of current phase‐contrast MR sequences are substantially smaller. The MR quantification of total coronary blood flow and coronary blood flow per gram of myocardium during stress and at rest seems to be an ideal method for evaluating coronary hemodynamics in diffuse myocardial diseases of the heart, such as hypertensive heart diseases and cardiomyopathies, and may be useful in evaluating endothelial dysfunction of the coronary circulation, which develops in the earliest stages of atherosclerotic disease and may precede obstruction of the epicardial coronary arteries.