The objective of this illustrative electronic presentation is to provide an understanding of the mechanics underpinning diffusion weighted imaging (DWI), and serves to guide parameter selection for optimal image formation. The hope is to leave the viewer intrigued and inspired to delve into the more advanced applications of DWI.

Diffusion weighted imaging (DWI) is a commonly employed MRI technique in the clinical setting.

Often used in imaging of the brain and increasingly in other parts of the body, routine applications of DWI include its role in the early diagnosis of acute strokes, its use in parametric assessment of body and pelvic malignancies, with more advanced applications including fiber tractography in brain and musculoskeletal studies.

The DWI pulse sequence is sensitized to the random molecular thermal motion of water molecules. Diffusion pulses cause the MR signal to diminish in proportion to the random velocities of diffusing water molecules.

This educational exhibit begins by covering the basic physics of diffusion, starting with the history of Brownian motion and its explanation by Einstein.

The exhibit uses various computer graphics and animations to show how magnetic resonance spin echoes are sensitive to diffusion, with descriptions of the main gradient encoding schemes, pulse sequences and fat suppression techniques used to produce qualitative diffusion-weighted MRI and quantitative images of apparent diffusion coefficient (ADC) maps.

Commonly encountered artifacts are described, such as geometrical distortion and eddy current artifacts along with tips to minimize their effects.

This is followed by a brief exploration of monoexponential and multiexponential modelling of biological processes involved in diffusion, including perfusion and the concept of intravoxel incoherent motion.

The exhibit concludes with a glimpse into diffusion anisotropy and an introduction to diffusion tracking imaging (DTI).