In which patients is diffusion-weighted magnetic resonance imaging most useful in routine stroke care?

Background and Purpose. Magnetic resonance (MR) diffusion-weighted imaging (DWI) has been used extensively in hyperacute cortical ischemic stroke, but its broader role in the assessment of patients presenting at later times after a wider variety of strokes has been less widely studied. Methods. The authors assessed the clinical usefulness of DWI across a range of patients referred prospectively as either inpatients or outpatients. Detailed clinical information was collected. Diffusion (DWI) and T2-weighted images were read separately and blindly to clinical details. The presence of any infarct and its type were noted. Results. In 153 stroke patients, imaged at a median of 2 days (range, 6 hours to 77 days) after stroke, recent infarcts were identified more often on DWI (70%) than on T2-weighted MRI (32%) in all severities of stroke. The proportion of scans on which relevant lesions were only seen on DWI was greatest among milder strokes due to small cortical or lacunar infarcts and among patients imaged later rather than earlier after the stroke. Conclusions. DWI is clinically useful up to several weeks after stroke, not just within the first few hours, and especially in patients with minor strokes.