Magnetic resonance imaging better than computed tomography for the detection of acute stroke

Magnetic resonance imaging (MRI) is better than the more commonly used computed tomography (CT) for the detection of acute stroke, according to an Article in this week's issue of The Lancet.

CT is the most common imaging modality used to assess patients with suspected stroke - it is widely available, fast, easy, and less expensive than MRI. However, previous studies have suggested that CT is insufficiently sensitive for the diagnosis of acute ischaemic stroke, is subject to substantial inter-rater variability in interpretation, and might not be better than MRI for detection of acute intracranial haemorrhage. MRI has been shown to offer advantages for the assessment of acute stroke - changes in acute ischaemic injury are detectable sooner than with CT, and MRI has greater interobserver and intraobserver reliability than CT, even in readers with little experience. Although the use of MRI for the diagnosis of acute stroke is increasing, this method has not yet been proved more effective than CT in the emergency setting.

Julio Chalela (now at Medical University of South Carolina, Charleston, SC, USA, but was at NINDS, NIH, Bethesda, Maryland, USA, when the study was conducted) and colleagues did a single-site prospective comparison of CT and MRI for the detection of acute stroke patients who presented for emergency assessment of stroke-like symptoms. 356 patients, 217 of whom had a final clinical diagnosis of acute stroke were assessed. The researchers found that MRI detected acute stroke (ischaemic or haemorrhagic), acute ischaemic stroke, and chronic haemorrhage more frequently than CT, and that MRI was similar to CT for the detection of acute intracranial haemorrhage. Relative to the final diagnosis, MRI had a sensitivity of 83% and CT 26% for the diagnosis of any acute stroke. The findings indicate that MRI should be the preferred test for accurate diagnosis of patients with suspected acute stroke.

The authors conclude: "Because our patient sample encompassed the range of the disease that is likely to be encountered in emergency cases of suspected stroke, our results are directly applicable to clinical practice."