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) k^psρ is the influx volume transfer constant (min^?1), or permeability surface area product per unit volume of tissue, between plasma and EES; (2) v_e is the volume of EES space per unit volume of tissue (0 < v_e < 1); and (3) k_ep, the efflux rate constant (min^?1), is the ratio of the first two parameters (k_ep = k^psρ/v_e). The ratio k_ep 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 k^psρ and v_e separately requires knowledge of T₁₀ and of the tissue relaxivity R₁ (≈? in vitro value).