Myocardial velocity gradient imaging by phase contrast MRI with application to regional function in myocardial ischemia

Velocity-encoded phase contrast magnetic resonance imaging (MRI) has the po tential to quantify regional myocardial contractile function with a sensiti vity to motion comparable to implanted ultrasonic crystals. An MRI sequence and postprocessing algorithm were developed to measure myocardial velocity gradients on a 1.5 T MRI scanner. These methods were validated on a rotati ng phantom and applied to dogs before (n = 11) and during prolonged coronar y occlusion (n = 5). In phantom validation studies, the average absolute er ror corresponded to motion equivalent to 0.03 +/- 0.04 mm (mean +/- SD) dur ing the repetition time of the experiment. Rigid body corrections during po st-processing significantly simplified the interpretation of myocardial vel ocity vectors. In vivo, rigid body motion contributes substantially to the recorded myocardial velocities in systole and diastole and can give the fal se impression of regional wall motion abnormalities. After rigid body corre ction, normal systolic and diastolic velocity vectors in short-axis views o f the left ventricle were primarily directed toward the center of the left ventricle. Transmural radial strain rate was 2.0 +/- 0.6 sec(-1) during sys tole and -3.6 +/- 1.1 sec(-1) during early diastole in normal canine hearts . Ischemic myocardium was easily discriminated from normal left ventricle b y velocity-encoded phase contrast MRI both qualitatively and quantitatively (P < 0.01 in systole and P < 0.05 in early diastole). Although the myocard ial velocity images have a spatial resolution on the order of a millimeter, the velocity encoding describes the mechanical consequences of focal myoca rdial ischemia with sensitivity to submillimeter displacement of the pixels . The three-dimensional nature of velocity-encoded MRI is particularly well suited to the study of the complex motion of the heart in vivo. Magn Reson Med 42:98-109, 1999. (C) 1999 Wiley-Liss, Inc.