Diffusion MRI: From Quantitative Measurement to In vivo Neuroanatomy

Developments in the last century have led to a better understanding of diffusion, the perpetual mixing of molecules caused by thermal motion. In this chapter, the basic principles governing the diffusion phenomenon and its measurement using magnetic resonance (MR) are reviewed. The concepts of the apparent diffusion coefficient and of the diffusion propagator as well as their MR measurements are introduced from basic principles. Finally, the influence of neural tissue microstructure on the diffusion-weighted MR signal is briefly discussed.