From: Role of diffusion weighted MR-imaging in the evaluation of malignant mediastinal lesions
High b value (DWI)
Facilitated diffusion (e.g. benign cyst)
Restricted diffusion (e.g. malignant tumor)
Pitfalls of DWI
T2 – Shine through effect
E.g. a cyst will demonstrate high signal intensity on T2-weighted images and on diffusion images obtained at high b values but also on the ADC map. Unlike a cyst, a region with truly restricted diffusion will demonstrate low signal intensity on the ADC map.
Slow-flowing blood within a region may demonstrate the signal intensity characteristics of a highly cellular lesion. This pitfall is readily observed on DWI of a hemangioma. In this situation, interpretation of the findings obtained with other MR sequences is very helpful.