Three major models (from Tofts, Larsson, and Brix) for collecting and analyzing dynamic MRI gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA) data are examined. All models use compartments representing the blood plasma and the abnormal extravascular extracellular space (EES), and they are intercompatible. All measure combinations of three parameters: (1) kpsρ is the influx volume transfer constant (min−1), or permeability surface area product per unit volume of tissue, between plasma and EES; (2) ve is the volume of EES space per unit volume of tissue (0 < ve < 1); and (3) kep, the efflux rate constant (min−1), is the ratio of the first two parameters (kep = kpsρ/ve). The ratio kep is the simplest to measure, requiring only signal linearity with Gd tracer concentration or, alternatively, a measurement of T1 before injection of Gd (T10). To measure the physiologic parameters kpsρ and ve separately requires knowledge of T10 and of the tissue relaxivity R1 (≈ in vitro value).