A person walks in after a minor collision. Airbag deployed, months of brain fog, and every ordinary image reads clean.
That does not mean nothing happened. It often means the change is real but sits below what any human eye can detect by looking.
The volume lost in a mild brain injury can be a small fraction of a small structure. No one is going to catch that by scrolling through images and squinting. To find it, you have to measure it, region by region, and compare against real reference values.
I have seen studies called unremarkable where the answer was waiting in the numbers the whole time. Same images. A different way of interrogating them.
The eye is unmatched for pattern and for the obvious catastrophe. It was never built to weigh a structure to the percent.
When the injury is subtle, looking harder is not enough. At some point you have to start counting.