The aim of this thesis was to explore applications of three selected, quantitative MRI makers: cerebral perfusion, the T2 of peripheral cerebrospinal fluid (CSF) and volumetric measures. The studied populations share a risk of future decline, where a patient’s functional status will either deteriorate, remain stable or recover. In part 1, we used quantitative MRI markers to investigate the impact of aneurysmal subarachnoid hemorrhage (aSAH) and traumatic brain injury (TBI) on the brain. Both conditions are characterized by a relatively young patient population and a substantial proportion of patients with poor functional outcome. In part 2, we investigated the three quantitative MRI markers to distinguish between individuals on the continuum between healthy aging and dementia.