COMPARISON OF ALBUMIN-(GD-DTPA)(30) AND GD-DTPA-24-CASCADE-POLYMER FOR MEASUREMENTS OF NORMAL AND ABNORMAL MICROVASCULAR PERMEABILITY

The purpose of this study was to compare a new MR macromolecular contr ast medium (MMCM), gadolinium-diethylenetriamine pentaacetic acid (Gd- DTPA)-24-cascade-polymer, to a well-studied prototype MMCM, for the po tential of distinguishing tissues of varying endothelial permeability. Three tissue models of varying capillary permeability were studied in a total of 46 rats: normal myocardium (normal capillaries), subcutane ously implanted adenocarcinoma (mild capillary leak), and reperfused i nfarcted myocardium (high capillary leak). T1-weighted MRI was perform ed before and dynamically after injection of either albumin-((Gd-DTPA) (30) or the cascade polymer (each .02 mmol gadolinium [Gd] per kg). Da ta analysis based on a two-compartment kinetic model yielded estimates of fractional blood volume (BV) (percentage) and fractional leak rate (FLR) (1 per hour). Permeability to the cascade polymer as reflected in FLR was considerable in normal myocardium (8.24 per hour), of simil ar value in tumors (8.55 per hour), but significantly greater in infar cted myocardium (39.17 per hour, P < .01) versus normal myocardium. Th e larger albumin-(Gd-DTPA)(30) demonstrated minimal extravasation in n ormal myocardium (FLR.33 per hour); FLR in tumors was 100% higher (.66 per hour, P < .002) and FLR in reperfused capillaries was significant ly greater (7.94 per hour, P < .001). Based on capillary permeability measurements, the cascade polymer may have limited utility for detecti on of mildly increased microvascular permeabilities. For severe tissue injury, the cascade polymer can resolve abnormal microvascular integr ity.