Diffusion weighted images

Basics:
Bright signal on DWI (B=1000) means restricted diffusion and/or T2 effect.
On ADC, low signal in the same region means restricted diffusion, and bright or isointense signal means T2 shine through effect.
On T2,  the same area may appear bright or isointense.

Pathologies with restricted diffusion:
Acute stroke, acute stroke, acute stroke... (repeat this 10 times before proceeding to next)
Infection: Herpes encephalitis, Pyogenic infection, CJD, meningoencephalitis
Epidermoid (ADC usually cannot be calculated)

Diffuse axonal injury
Oxyhemoglobin (intracellular and hyperacute) (extracellular methHb shows increased signal on both DWI and ADC!)

A few acute MS lesions
Post-ictal
Susceptibility artefact: in inferior frontal and temporal regions should not be mistaken for restricted diffusion


Non-restricted diffusion:
Infection: HIV encepahlopathy
Tumor: primary or secondary, arachnoid cyst
Inflammation: most acute MS lesions
Chronic lesions: chronic stroke, gliosis, neuronal loss
Others: hypertensive encephalopathy, clyclosporin toxicity, hyperperfusion after endartertectomy