A myocardial perfusion reserve index in humans using first-pass contrast-enhanced magnetic resonance imaging

OBJECTIVES The purpose of this study was to evaluate a myocardial perfusion reserve index (MPRI) derived from a quantitative magnetic resonance imagin g (MRI) technique in normal human volunteers and patients with coronary art ery disease and to relate MPRI to coronary artery stenosis severity measure d with quantitative arteriography. BACKGROUND Magnetic resonance imaging could be a useful noninvasive tool in the investigation of ischemic heart disease. However, there have been few studies in humans to quantify myocardial perfusion and myocardial perfusion reserve using MRT and none in patients with coronary disease. METHODS Twenty patients with angiographically proven coronary artery diseas e and five normal volunteers underwent both resting and stress (adenosine 1 40 mu g/kg(-1)/min(-1)) first-pass contrast-enhanced MRI examinations (usin g 0.05 nmol/kg(-1) of gadopentetate dimeglumine. Using a tracer kinetic mod el, the unidirectional transfer constant (K-i), a Perfusion marker for the myocardial uptake of contrast, was computed in each coronary arterial terri tory. The ratio of K-i for the rest and stress scans was used to calculate the MPRI. Percent reduction in lumina diameter of coronary lesions was meas ured using an automated edge-detection algorithm. RESULTS Myocardial perfusion reserve index was significantly reduced in pat ients compared with norma. subjects (2.02 +/- 0.7 vs. 4.21 +/- 1.16, p < 0. 02). For regions supplied by individual vessels, there was a significant ne gative correlation of MPRI with percent diameter stenosis, (r = -0.81, p < 0.01). Importantly, regions supplied by vessels with; <40% diameter stenosi s (non-flow limiting) had a significantly higher MPRI than regions supplied by stenoses of "intermediate" severity, that is, >40% to 59% diameter sten osis (2.80 +/- 0.77 and 1.93 +/- 0.38, respectively, p < 0.02). However, ev en regions supplied by vessels with <40% diameter stenosis had a significan tly lower MPRI than volunteers (p < 0.01). CONCLUSIONS A myocardial perfusion reserve index derived from first-pass MR I studies can distinguish between normal subjects and patients with coronar y artery disease. Furthermore, it provides useful functional information on coronary lesions, particularly where the physiologic significance cannot b e predicted accurately from the angiogram, (C) 1999 by the American College of Cardiology.