Diffusion-Weighted Imaging

One of the great developments in MRI in the past few years has been Diffusion-Weighted Imaging. This is most useful to us in the assessment of patients with stroke-like symptoms of recent onset. The technique sensitively and accurately identifies areas of limited water diffusion, most importantly in areas of recent brain infarction.

Early in the process of infarction, when cell homeostasis mechanisms fail but before cell membranes break apart, the cells swell and the space surrounding them becomes obliterated. Water diffusion in the extracellular spaces thereby becomes limited. Special MRI sequences are able to measure very small movements of water molecules. Capitalizing on this, visual representations of relative differences in water diffusion through the tissues is created. For example, a Diffusion-weighted image makes an otherwise very subtle site of recent infarct stand out as bright white. An Apparent Diffusion Coefficient (ADC) map adds specificity, showing areas of limited water diffusion as a dark spot while areas of unlimited water movement such as the CSF in the ventricles appears white.

Diffusion-Weighted MR Imaging allows high sensitivity for detection of early infarction in the brain and high specificity to distinguish acute infarction from other pathology such as tumor-associated tissue edema or chronic microvascular ischemic changes in the white matter.

These sequences are now included routinely in all MRI Brain exams at each of our practice locations.