A standard brain image shows you structures. It is far harder to show you circuits.
White matter is the wiring that connects the brain to itself. Diffusion imaging lets us follow those cables and put a number on how organized they are, a value that tracks with how well a bundle is functioning.
That matters because so much of what a person actually experiences lives in the wiring. The bundle that carries memory and mood. The great bridge that links the left and right halves. The tracts that route language, vision, and coordinated movement.
When one of those bundles reads statistically low, we are not guessing that something feels off. We are seeing a specific circuit that is underperforming for that person.
A brain can look structurally intact and still be miswired in a way that changes a life.
Reading only the anatomy answers half the question. The other half is in the connections.