The blood-tissue exchange kinetics of gadopentetate were studied in 49 malignant and benign mammary tumors. Signal enhancement was monitored simultaneously in the aorta and in tumor for 10.5 minutes after the beginning of a 1 minute i.v. infusion of the contrast medium (CM), Kinetic analysis was based on a model with two compartments for systemic pharmacokinetics and up to three kinetically distinct compartments for tumor. Kinetic heterogeneity, ie, two or more compartments with different exchange rate constants in a given tumor, was found in 85% of carcinomas, 38% of fibroadenomas, and 14% of mastopathic tumors. The within-tumor average of CM exchange rates was 1.22 (0.62-1.65) min(-1) in carcinomas, 0.38 (0.26-0.60) min(-1) in fibroadenomas, and 0.16 (0.12-0.20) min(-1) in mastopathies (median and interquartile distances). The area under the signal enhancement-time curve of the aorta varied 4.5-fold between individuals. It is concluded that individual CM kinetics in arterial blood should be taken into account when CM exchange rates between blood and tumor are to be determined and that a kinetic model for potentially malignant tumors should allow for kinetic heterogeneity. (C) 1999 Wiley-Liss, Inc.
