DWI is a form of MR Imaging based upon measuring the random Brownian motion of water molecule within voxel of tissue.
In generally simplified term Highly Cellular tissue or Those with Cellular Swelling exhibit Lower Diffusion Coefficient.
Diffusion is particularly useful in Tumour Characterisation and Cerebral Ischemic .
A great deal of confusion exists in the way the clinician and radiologist refer to diffusion restriction , with both groups often appearing to not actually understand what they are referring to.
The term of Diffusion Weighted Imaging is used to denote a number of different thing .
1. Isotropic Diffusion Map ( What the radiologist and Clinician will refer to as DWI ).
2. The various Pulse sequence that result in the generation of various images ( Isotropic map , B:0 , adc).
3. The more general term to encompass all diffusion technique including diffusion tensor imaging .
To make matters worse, many are not aware of the concept of T2 shine-through, a cause of artefactual high signal on isotropic maps, or interpret it as a binary feature with T2 contribution to signal either present or absent when in reality there is always a T2 component even to regions with true T2 diffusion restriction.
A much safer and more accurate way of referring to diffusion restriction is to remember that we are referring to actual apparent diffusion coefficient (ADC) values, and to use wording such as "the region demonstrates abnormally low ADC values (abnormal diffusion restriction)" or even "high signal on isotropic images (DWI) is confirmed by ADC maps to represent abnormal restricted diffusion".
