AbstractDiffusion‐weighted images of the rat brain were obtained using the pulsed‐gradient spinecho method. An attempt was made to extract perfusion‐related parameters from signal intensity data taken from the caudate‐putamen region of the images, by using a nonlinear least‐squares calculation to fit the Le Bihan biexponential expression (Le Bihan et al., Radiology, 168, 497 (1988)) to the data. The perfusion‐related parameters could not be obtained with sufficient accuracy to be useful, although the perfusion‐weighted images appear to contain meaningful qualitative information. An analysis of the perfusion model is presented and shows why the Le Bihan pseudo‐diffusion coefficient is particularly difficult to measure with reasonable accuracy. © 1992 Academic Press, Inc.