General Principles and Challenges of Diffusion MRI

The concept of diffusion magnetic resonance imaging (MRI) emerged in the mid-1980s as a way to probe tissue structure. Diffusion MRI is both a method and a powerful concept, as diffusing water molecules provide unique information on the tissue microscopic architecture. Diffusion MRI was initially used to investigate neurological disorders but has been shown to work in the body as well, in particular in the breast. Water diffusion is significantly reduced in most malignant tissues, and diffusion MRI, which does not require any tracer injection, is rapidly becoming a modality of choice to detect, characterize, or even grade malignant lesions, and also for monitoring therapy. The classic quantitative marker of diffusion MRI is the apparent diffusion coefficient (ADC). This chapter reviews the basic principles underlying diffusion MRI and introduces advances beyond the ADC, such as non-Gaussian diffusion, perfusion-driven IVIM, diffusion tensor imaging (DTI), and technical limitations.