Abstract

Cardiac diffusion MRI with diffusion encoding that spans a cardiac cycle is complicated by myocardial strains. This paper presents a method to obtain accurate diffusion data without strain correction. Owing to the synchrony of normal cardiac motion, there are time points in the cardiac cycle, "sweet spots," when the cardiac configuration approximates its temporal mean. If the diffusion is encoded then, the net effect of strain on the observed diffusion approximates zero. To test this, MRI diffusion and strain-rate movies are performed on cyclically deformed gel phantoms and in five normal subjects. In phantoms, the sweet spots predicted from the strain time curves agree with the times when the observed diffusion equals the true diffusion. In humans, the strain prediction of the sweet spots and the locations determined by the diffusion trace show a high correlation, r = 0.99. In all subjects, diffusion MRI presents a fiber orientation pattern comparable to that obtained from a stationary specimen. Magn Reson Med 42:393-403, 1999.