Quantification of tissue plasma volume in the rat by contrast‐enhanced magnetic resonance imaging

Magnetic resonance imaging enhanced with a macromolecular contrast medium (MMCM), albumin‐Gd‐DTPA, was used to estimate the plasma volume in vivo in the myocardium, lung, liver, and skeletal muscle of 10 normal rats. The plasma volumes of the same tissues in a parallel group of six rats were estimated in vitro by a conventional radioisotopic technique (111In‐transferrin). Plasma volumes of myocardium, lung, liver, and skeletal muscle estimated by the MR technique (μl plas. ia cc‐1 of tissue) were 101,109,163, and 11.0, respectively, while plasma volumes measured by the In‐transferrin radioisotope technique (mg plasma g‐1 of tissue) were 78.6, 215,143, and 11‐2, respectively. Assuming a ratio of densities of aerated lung to blood of 0.45 and of other tissues to blood of 1.0, correlation between the methods was excellent (R2 = 0.99) indicating that MR imaging enhanced with MMCM permits reliable in vivo estimation of tissue plasma volume in the rat.