Recent development in the use of magnetic resonance imaging (MRI) to measure and image molecular diffusion and blood microcirculation (perfusion) hold significant promise in the non-invasive evaluation of cerebral tissue perfusion. Functional MRI shows brain ischemia at a very early stage has the potential to differentiate ischaemic tissue from traumatized tissue and can detect the threshold between reversible and irreversible ischaemic injury following closed head injury. Moreover, functional MRI may reveal areas of cerebral dysfunction in regions that look structurally intact on CT or MRI and can improve the ability to predict long term neurologic and functional outcome. The aim of this thesis is to highlight outcome prediction based upon cerebral perfusion in adult patients with moderate and severe head injuries.