About one-quarter of acute stroke cases with an initially negative head CT will have an MRI with evidence of An emergency depart- ment series of 252 patients presenting with atypical stroke symptoms and a negative CT found that 29 patients (11.5%) had acute ischemic stroke on MRI For posterior circulation strokes in particular, a follow-up MRI may be appro- priate to confirm a diagnosis even when the initial MRI is negative.64 MRI with diffusion-weighted imag- ing is also particularly helpful in evaluating patients with low-risk TIA and mild neurological symptoms.85 Confirming the diagnosis of acute ischemic stroke with brain imaging may help with patient education and prognostication, which in turn may promote adherence to a prescribed prevention regimen.65 9. About one-third of patients with stroke symptoms for <24 hours have a diffusion-weighted imaging A cost-effectiveness analysis of the use of MRI in patients with TIA reported in 2014 concluded that MRI was generally not cost- effective, although there might be utility to MRI in this population if the imaging is done >1 week after onset of symptoms and with a blood-sensitive sequence, if the clinical team is considering unusual causes of symptoms, or if symptoms are related to ipsilateral high-grade stenosis.69 Predictive scores that incorporate MRI findings (eg, ABCD2 -I and -I) are better able to discriminate high risk of early stroke from low risk of early stroke than predictive scores that do not incorporate MRI find- ings (eg, ABCD2 ) when MRI is done within 7 days of onset of symptoms.67 10. Stroke can be the initial manifestation of a host of systemic conditions that either are treatable by themselves or must be identified to avoid misdi- rected ineffective or harmful therapies. 