How do you identify brain damage from head trauma or from a concussion, a year after the fact?

Formation of scar ..: Tissue sometimes occurs after head trauma. It is more likely and involves a larger area if the trauma is more severe. These areas of scarring can sometimes be identified on an MRI of the head. Unless there is an MRI of the head performed before the trauma, it is often impossible to absolutely state that a particular abnormal area on the MRI is caused by a particular traumatic event.

Possibly by MRIs: Mri technology has advanced dramatically in the last few years. Specialized sequences looking at the white fiber tracts or looking for signs of micro hemorrhages (t2-star sequences) are useful for detecting abnormalities. If the head injury is more severe clinically, there are usually more findings on mri. These may be followed over time with serial MRI scans to see if they hopefully improve.