Experimental Models of Brain Disease: MRI Contrast Mechanisms for the Assessment of Pathophysio logical Status

Magnetic resonance imaging (MRI) is a technique allowing non-invasive in vivo imaging with excellent discrimination between different types of soft tissue. The contrast in a standard MR image depends both upon variations in tissue water density and the physicochemical environment of the water. For this reason, it is not only possible to differentiate tissue types [e.g. gray matter, white matter, and cerebrospinal fluid (CSF) in the brain] but also normal and abnormal physiological states (e.g. to identify regions of cerebral edema following a stroke). More recently, methods have been developed, which allow more dynamic assessment of changing physiological parameters, either through their effect on MR relaxation parameters or via some other modulation of the MR signal. In this chapter, the most common MR methods used for imaging the brain will be described, and the mechanisms responsible for the sensitivity of these methods to pathophysiology in brain disease will be explained.