[Flow quantification in coronary and bypass vessels with MR phase contrast technique]

To evaluate accuracy of velocity encoded cine MR imaging for determination of blood flow in coronary arteries and coronary bypass grafts.12 patients with 22 coronary bypass grafts underwent intraoperative flow quantification using the transit time ultrasound method. These values were compared to postoperative MR phase shift measurements. Flow measurements were performed preoperatively in 28 coronary arteries of 20 patients. For flow measurement, we used a velocity-encoded k-space segmented gradient echo sequence with a temporal resolution of 110 or 125 ms, respectively. 6-8 pase shift images could be acquired during one cardiac cycle.There was a significant correlation between intraoperative and flow measurements using velocity-encoded MR imaging (r = 0.74, p0.0001, t-test). Flow volumes determined by MR imaging were systematically larger than those determined by the transit time ultrasound method. Mean flow in coronary arteries was reduced in severely stenosed vessels (70%) compared to normal vessels. Intra- and interobserver variability were 10.5 and 15% (coronary bypass grafts), and 12.3 and 15.8% (coronary arteries), respectively.Velocity-encoded MR imaging enables determination of flow in coronary artery bypass grafts and coronary arteries. Future developments should aim at the improvement of spatial and temporal resolution of the method.