MIT Technology Review describes this promising imaging modality:
It uses magnetic resonance signals to track the movement of water molecules in the brain: water diffuses along the length of neural wires, called axons. Scientists can use these diffusion measurements to map the wires, creating a detailed blueprint of the brain's connectivity.
On the medical side, radiologists are beginning to use the technology to map the brain prior to surgery, for example, to avoid important fiber tracts when removing a brain tumor. Wedeen and others are now using diffusion imaging to better understand the structures that underlie our ability to see, to speak, and to remember. Scientists also hope that the techniques will grant new insight into diseases linked to abnormal wiring, such as schizophrenia and autism