Variability of myocardial signal on magnetic resonance images.

The diagnosis of myocardial disease by magnetic resonance (MR) imaging depends on accurate measurement of myocardial signal intensity. The authors performed 15 experiments in four rabbits at 1.9 T with spin-echo MR imaging to study the variability of myocardial signal intensity throughout the cardiac cycle and to measure myocardial T2 values. Variability in signal from the myocardium throughout the cardiac cycle was observed in all experiments. During systole, a significant increase in myocardial signal was noted, when data acquisition was performed with electrocardiogram (ECG)-gating and controlled ventilation (P = .02). An inverse relationship between myocardial signal and phase noise was found, indicating the motion-related nature of the variation of myocardial signal. A similar inverse relationship was observed in images obtained from a normal human volunteer. Ex vivo myocardial T2 values of rabbit myocardial tissue were significantly higher than the in vivo values (P = .003), reflecting residual motion despite cardiac gating and controlled ventilation.