MR imaging measurement of compartmental water diffusion in perfused heart slices

Myocardial tissue slices were isolated from the left ventricular free wall (7 slices) and left ventricular papillary muscle (3 slices) of New Zealand White male rabbits (n = 4) and were subsequently superfused with a modified St. Thomas' Hospital cardioplegic solution at 19 degreesC. The diffusion-w eighted images were obtained with a 600-MHz nuclear magnetic resonance spec trometer using diffusion gradient b-values that ranged from 166 to 6.408 s/ mm(2); the apparent diffusion coefficient of water in the tissues were subs equently calculated. All of the tissue samples that were studied exhibited nonmonoexponential diffusion. Data from seven slices were mathematically fi tted by a biexponential expression with a fast diffusion component of 0.72 +/- 0.07 x 10(-3) MM2/s, and a slow diffusion component of 0.060 +/- 0.033 X 10(-3) mm(2)/s. The fast component dominated the calculated apparent diff usion coefficient of the tissue, composed of 82 +/- 3% of the overall diffu sion-dependent signal decay. Thus myocardial tissue exhibits characteristic s consistent with multiple compartments of diffusion. This work has importa nt implications for myocardial diffusion tensor imaging, as well as the cha nges in diffusion that have been reported following myocardial ischemia.