QUANTITATIVE REGIONAL BLOOD-VOLUME STUDIES IN RAT MYOCARDIUM IN-VIVO

Many pathophysiological processes in the myocardium are in close relat ion to changes of the regional blood volume and regional myocardial bl ood flow or perfusion. Only few methods exist to obtain quantitative v alues for these parameters. Quantitative regional blood volume (RBV) s tudies in rat myocardium are presented using snapshot fast low angle s hot (FLASH) inversion recovery T-1 measurements with two different blo od pool contrast agents, gadolinium diethylenetriaminopentaacetic acid (Gd-DTPA) albumin and Gd-DTPA polylysine. In contrast to previous att empts, each snapshot FLASH image acquisition was EGG-triggered under b reathhold conditions. To measure relaxation times shorter than a heart cycle, each T-1 sequence was repeated two times with different delays between inversion pulse and first image acquisition. The experiments were performed on a Bruker Biospec 70/21 using a homogeneous transmitt er coil and a circularly polarized surface receiver coil, a special EC G trigger unit, and a respirator that is controlled by the pulse progr am. Based on a fast exchange model RBV, maps were calculated from the relaxation time maps for different concentrations of the two blood poo l contrast agents, A significant dependence of the RBVm values on bloo d T-1 was found. This is in accordance with a model that has been deve loped recently relating the dependence of RBVm on T-1 of blood to perf usion. For Gd-DTPA albumin, the application of the model to the experi mental data yields realistic values for RBV and perfusion, The values, which are in accordance with literature data, were obtained at highes t contrast agent concentrations i.e., lowest relaxation times of blood (ca, 200 ms).