OPTIMIZATION OF MAGNETIC-RESONANCE-IMAGING PARAMETERS FOR LEFT-VENTRICULAR WALL-MOTION STUDIES AT 0.5 T

Magnetic resonance cine imaging of left ventricular wall motion at res t or during stress may be used to assess myocardial function, infarcti on and viability, or reversible ischaemia. Whilst interpretation of th e cines rests critically on image quality, there is little in the lite rature which systematically examines the optimal imaging parameters fo r such wall motion studies at rest or during stress. This study was de signed to examine several imaging parameters for cine optimization usi ng a conventional 0.5 T scanner. Gradient echo imaging was performed i n two groups of volunteers with varying echo times and flip angles. Th e period between excitations was 80 ms (simulating a resting heart rat e) in one group, and 40 ms (simulating tachycardia during stress) in t he other group. Short axis imaging yielded the highest contrast betwee n blood and myocardium for both repetition times (rest p = 0.02; stres s p<0.001) compared with the long axes, because of magnetic saturation of blood moving slowly in-plane. Contrast was higher at end-diastole than end-systole for the long axes (rest p<0.0001; stress p<0.0002), b ut not significantly different in the short axis. Increasing the echo time and flip angle resulted in increased signal but eventually caused motion artefact and magnetic saturation of blood. The optimal paramet ers were an echo time of 14 ms and a 45 degrees flip angle for resting heart rates, with the flip angle falling to between 35 degrees and 45 degrees for tachycardia. The choice of imaging parameters is therefor e a compromise between improved signal and unwanted artefacts, althoug h the latter are less evident in the short axis plane, which yields th e best contrast results because of high blood inflow effects.