From a historical perspective, the main clinical utility of MRI has been its strength in superior resolution of neurological soft tissues, far more than that is able to be seen with Computed Tomography (CT).
MRI easily distinguishes grey from white matter, excludes focal intracerebral (or intra-axial) lesions from extra-axial lesions and can perform angiography of the circle of Willis without the need for contrast.
Common conditions requiring MRI evaluation include demyelination disorders such as multiple sclerosis (MS), primary and secondary tumours, strokes, aneurysms and infections. All these may result in a positive clinical history of headaches and/or seizures, making MRI the imaging modality of choice.
CT is the main imaging modality used in the context of trauma as it is widely available and reliably demonstrates haemorrhage from normal cerebral tissue. The main disadvantage of CT is the use of ionising radiation.