Utility of Diffusion Weighted Imaging as a Problem Solving Sequence on Brain MRI

Purpose: Diffusion weighted imaging uses varying gradient strengths in order to dephase the imaged tissue resulting in decreased signal return. The further water moves (diffuses) the more it will be dephased. Therefore, water molecules that are trapped will have less exposure to the varying gradient strengths allowing them to maintain a relatively elevated signal. Different disease processes display different mechanisms responsible for restricted diffusion, including cytotoxic edema, hypercellularity, viscous fluid, demyelination, etc. While all these mechanisms can lead to restricted diffusion, there are characteristic patterns which can be invaluable when making a diagnosis.

Methods/Materials: Although many disease processes can restrict the diffusivity of water molecules, there are specific patterns of restriction which can be of vital importance. These specific patterns of restricted diffusion can help to narrow the differential diagnosis and make a dramatic difference for the patient. Some of the specific patterns to be discussed include the presentation of ischemic stroke, abscess, hypercellular tumor including primary CNS lymphoma, demyelination, encephalitis, epidermoid cyst, Creutzfeldt-Jakob disease, diffuse axonal injury, and intracranial hemorrhage on diffusion weighted imaging. A few sequences (prior to the DWI) will be shown per case to allow the participant to develop a differential diagnosis. Following the initial sequences and development of a differential, the DWI sequence will be shown with emphasis on the specific features in hopes to improve diagnostic accuracy amongst the participants.

Results: Diffusion weighted imaging can be an excellent problem solving sequence in cases where there is a diagnostic dilemma. Familiarity with specific patterns can aid physicians in the formation of a more accurate differential.

Conclusions: As demonstrated in this exhibit, there are many causes of restricted diffusion. Although there is overlap, there are also specific patterns of restricted diffusion. Familiarity with these patterns along with the patient specific clinical information will aid in the formation of a focused differential.