Diagnostic approach to functional recovery: diffusion-weighted imaging and tractography.

There is evidence showing that white matter changes are clinically relevant and can be associated with cognitive disorders, slower mental processing speed or motor impairment. The complex structural organization of the white matter can be depicted in vivo in great detail with advanced diffusion-weighted imaging (DWI). From the simplest and most commonly used technique (e.g. the mapping of apparent diffusion coefficient values) to more advanced techniques (e.g. diffusion tensor imaging), it is now possible to visualize white matter fibers of the brain in a noninvasive way. This chapter will first provide a basic understanding of the principles of these techniques and describe the current clinical applications of DWI and tractography in two common brain diseases, stroke and traumatic brain injury. We will emphasise on what these techniques may add to our understanding of the natural course of the pathology and especially, how they can help in predicting the outcomes of the rehabilitation phase. We will discuss how DWI and tractography techniques can shed light on possible compensatory disease mechanisms and propose future developments of these techniques in a clinical setting.