Quantifying myocardial blood flow and resistance using 4D-flow cardiac magnetic resonance imaging

Background. Ischaemia with nonobstructive coronary arteries is most commonly caused by coronary microvascular dysfunction but remains difcult to diagnose without invasive testing. Myocardial blood fow (MBF) can be quantifed noninvasively on stress perfusion cardiac magnetic resonance (CMR) or positron emission tomography but neither is routinely used in clinical practice due to practical and technical constraints. Quantifcation of coronary sinus (CS) fow may represent a simpler method for CMR MBF quantifcation. 4D fow CMR ofers comprehensive intracardiac and transvalvular fow quantifcation. However, it is feasibility to quantify MBF remains unknown. Methods. Patients with acute myocardial infarction (MI) and healthy volunteers underwent CMR. Te CS contours were traced from the 2-chamber view. A reformatted phase contrast plane was generated through the CS, and fow was quantifed using 4D fow CMR over the cardiac cycle and normalised for myocardial mass. MBF and resistance (MyoR) was determined in ten healthy volunteers, ten patients with myocardial infarction (MI) without microvascular obstruction (MVO), and ten with known MVO. Results. MBF was quantifed in all 30 subjects. MBF was highest in healthy controls (123.8 ± 48.4 mL/min), signifcantly lower in those with MI (85.7 ± 30.5 mL/min), and even lower in those with MI and MVO (67.9 ± 29.2 mL/min/) (P < 0.01 for both diferences). Compared with healthy controls, MyoR was higher in those with MI and even higher in those with MI and MVO (0.79 (±0.35) versus 1.10 (±0.50) versus 1.50 (±0.69), P = 0.02). Conclusions. MBF and MyoR can be quantifed from 4D fow CMR. Resting MBF was reduced in patients with MI and MVO.