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 (microliter plasma cc-1 of tissue) were 101, 109, 163, and 11.0, respectively, while plasma volumes measured by the 111In-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.