I received a question about resources to help with diagnosis involving diffusion-weighted imaging. Needless to say, this is a huge topic, but here are two sources that might help.
Imaging tutorial: differential diagnosis of bright lesions on diffusion-weighted MRI. (no PDF available, this is online only)
Diffusion-weighted MR imaging of the brain (in particular, I would look at the chapter "How to use this book," which groups similar image patterns together to ease diagnosis)