 - 1. Penetrating Skull Damage 2. Pregnancy 3. Hb 6,5 mmoll unless patient is known to have no history of cardiovascular disease, in which case a Hb 5,5 mmoll, will be the exclusion criterion 4. pH 7,1 at initial arterial blood analysis 5. Previous neurotrauma 6. Current exposure to radiation in the workplace, or history of participation in nuclear medicine procedures, including research protocols 7. Condition which would exclude a clinical MR scan e.g. pacemaker, shrapnel, metallic prosthesis 