The most common diagnostic investigation of Traumatic Brain Injury (TBI) in the ER is the CAT scan. CAT is an acronym for Computerized Axial Tomography. It is basically an X-ray that is computerized to produce images. In cases where the Traumatic Brain injury (TBI) occurs deeper inside the brain and not on the superficial aspects of the brain, a CAT will likely not detect a Traumatic Brain Injury (TBI). Hence when there is no bleeding or bruising of the surface of the brain, a CAT will not detect Traumatic Brain Injury (TBI)