The Use of Diffusion-Weighted Magnetic Resonance Imaging to Identify Infarctions in Patients With Minor Strokes Joanna M. Wardlaw, FRCP,FRCR,MD, Paul Armitage, BSc, Martin S. Dennis, FRCP,MD, Stephanie Lewis, PhD, Ian Marshall, MA, PhD, and Robin Sellar, FRCP,FRCR Background: Diffusion-weighted magnetic resonance imaging (DWI) shows cerebral infarction within minutes of its occurrence, but its value in clinical management after the stroke is less clear. We evaluated DWI scans in patients with minor strokes to determine whether DWI was helpful in identifying the stroke lesion and how long after the stroke could DWI still identify the lesion. Method: Patients admitted to our hospital with symptoms of a lacunar or minor cortical or posterior fossa stroke underwent T2 and proton density magnetic resonance imaging (MRI) of the brain, followed by DWI on a 1.5 Tesla Siemens scanner. The individual MR sequence images were examined (blind to each other and clinical information) to identify any recent infarction. Results: In 40 subjects (13 lacunes, 17 cortical, 5 posterior circula- tion infarctions, 2 transient ischemic attacks [TIAs] and 3 non-stroke), DWI scans showed the recent infarction clearly (even tiny ones) in 24 subjects (60%), in 12 of whom no infarction was visible on the T2 or proton density images. DWI also correctly excluded infarction in patients subsequently found not to have had a stroke. The diffusion abnormality was visible for up to 23 days after the stroke. Conclusion: DWI is useful for pinpointing the site of small infarctions that are either not visible or not distinguishable from previous lesions on T2 or proton density MRI, up to at least 3 weeks after the stroke. This may assist with planning further management of the stroke. The clinical use of DWI should not be restricted to just the first few hours after the stroke. Key Words: Stroke-MZerebral infarction-- Cerebrovascular disease--Magnetic resonance imaging--Diffusion imaging. Diffusion-weighted magnetic resonance imaging (DWI) is a technique that has shown ischemic areas within minutes of stroke in animal studies and within an hour in patients. 1 Delineation of the extent of ischemic tissue very From the Departments of Clinical Neurosciences, Medical Physics, and Radiology, Western General Hospital NHS Trust, Edinburgh, UK. Received February 11, 1999; accepted August 27, 1999. Supported by the Scottish Office Chief Scientist's Office and performed as part of the UK Medical Research Council Clinical Research Initiative in Clinical Neurosciences. Address reprint requests to Joanna Wardlaw, FRCP, FRCR, MD, Department of Clinical Neurosciences, Western General Hospital NHS Trust, Bramwell Dott Building, Crewe Road, Edinburgh EH4 2XU, UK. Copyright 9 2000 by National Stroke Association 1052-3057/00/0902-000353.00/0 early after stroke may eventually help guide acute treat- ment and provide a surrogate outcome measure for stroke treatment trials. 2,3 Most interest has therefore focused on using DWI in the hyperacute phase of stroke. 3-11 In view of the apparent sensitivity of DWI in detecting ischemia, however, we thought that DWI scanning might detect very small cortical and subcortical lesions not visible on conventional T2 or proton density (PD) mag- netic resonance imaging (MRI) scans, which would be clinically useful. Identifying the site of infarction may help to distinguish stroke symptoms from other condi- tions that mimick stroke, to determine whether carotid endarterectomy would be appropriate, or if the patient has suffered a new stroke on a background of a previous stroke, or if the patient's symptoms are caused by an intercurrent illness. Patients with minor strokes may 70 Journal of Stroke and Cerebrovascular Diseases, Vol. 9, No. 2 (March-April), 2000: pp 70-75