MR imaging of microvasculature

An imaging technique is proposed in which the contrast is correlated to the morphology of capillaries and other small blood vessels. The technique is based on measurements of the relaxation rates 1/T-2 and 1/T-2* before and a fter the injection of a contrast agent. An image is then formed by mapping the quantity Q = Delta R-2/(Delta R-2*)(2/3), where Delta R-2 and Delta R-2 * are the changes in the THEORY relaxation rates due to the contrast agent. If the contrast agent concentration is sufficiently high, it is shown that Q is given approximately by a simple analytic formula that involves only i ntrinsic properties of the vascular network and the rate of diffusion. In p articular, Q is sensitive to the histologic vessel density. Theoretical pre dictions for Q are shown to be consistent with experimental data obtained w ith a rat glioma model and normal cerebral cortex. The imaging technique ma y be useful in characterizing tumor angiogenesis. Magn Reson Med 44:224-230 , 2000. (C) 2000 Wiley-Liss, Inc.