Modeling tracer kinetics in dynamic Gd‐DTPA MR imaging

Abstract

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 (T 10). To measure the physiologic parameters k psρ and v e separately requires knowledge of T 10 and of the tissue relaxivity R 1 (≈︁ in vitro value).