Diffusion-Based MRI-Imaging Basics and Clinical Applications

Diffusion-weighted imaging (DWI) is an accepted and widely used MRI technique in clinical routine and research imaging. DWI image contrast is based on water molecule displacement at a micrometer scale. DWI, therefore, does not excel at high anatomic accuracy but provides a physically meaningful parameter for tissue characterization. Pathologic tissue changes often go along with changes in diffusion properties, which makes DWI so useful clinically. In contrast to water molecules diffusing freely in an open system, diffusion in biological tissues is restricted and influenced in many ways. The main diffusion barriers that are probed with DWI are cell membranes. Depending on the density and orientation of cell membranes in a given tissue, the diffusion of water molecules is influenced by both magnitude and orientation. DWI is a relatively fast and robust imaging technique, which makes its integration into a clinical imaging protocol relatively easy. For almost 30 years, DWI has been an indispensable imaging tool in the diagnostic workup of cerebral stroke imaging and in recent years has also become an important cornerstone in cancer imaging. It has been widely demonstrated that DWI and its advanced derivatives (diffusion tensor imaging, diffusion kurtosis imaging, etc.) all provide meaningful tissue characterization parameters. Higher image resolution, reduced image distortion artifacts, and standardized DWI protocols will further enhance the benefits of DWI in many clinical applications and improve diagnostic accuracy and patient care.