To demonstrate that CTP is useful for assessing patients with severe TBI, the investigators will conduct a large study at multiple hospitals across Canada. Before conducting the large study, the investigators need to make sure that it is feasible to add CTP of the head to the routine imaging that patients with severe TBI undergo at the time of their arrival at the hospital. The current study is a pilot study to test the feasibility of adding CTP imaging of the head to the routine imaging protocol for patients with severe TBI at the time of their hospital admission. The proposed feasibility study will help determine how many participants the investigators need for the larger study to attain a significant result and whether the investigators need to modify the investigators study methods.