Introduction

Magnetic resonance imaging is a sensitive method to detect disease in the central nervous system and monitor its progress. The magnetic resonance technique particularly reflects the amount of tissue water predominantly in the extracellular compartment. Experimental studies have shown its ability to monitor inflammation in the tissue (Hawkins et al., 1990) and also to discriminate extracellular from intracellular edema, and gliosis (Barnes et al., 1987, 1988).

With the introduction of the contrast agent gadolinium-DTPA, it is possible to detect bloodbrain barrier breakdown in vivo (Weinmann et al., 1984; Hawkins et al., 1990, 1992). For example, in multiple sclerosis gadolinium enhancement has been shown to be a frequent, early and important feature of the evolving multiple sclerosis plaque and has been used in recent treatment trials as a marker of inflammatory disease activity (Grossman et al., 1986; Gonzalez-Scarano et al., 1987; Kappos et al., 1988; Miller et al., 1988; Kermode et al., 1990)-see Fig. 16.1.

In early studies gadolinium enhanced MRI was used to assess the degree and distribution of Blood–brain barrier breakdown in experimental allergic encephalomyelitis, an animal model similar to multiple sclerosis. The pattern of barrier breakdown in the acute phase of the condition was compared to that of chronic relapsing disease (Hawkins et al., 1991).