Elsevier

The Lancet

Volume 369, Issue 9558, 27 January–2 February 2007, Pages 293-298
The Lancet

Articles
Magnetic resonance imaging and computed tomography in emergency assessment of patients with suspected acute stroke: a prospective comparison

https://doi.org/10.1016/S0140-6736(07)60151-2Get rights and content

Summary

Background

Although the use of magnetic resonance imaging (MRI) for the diagnosis of acute stroke is increasing, this method has not proved more effective than computed tomography (CT) in the emergency setting. We aimed to prospectively compare CT and MRI for emergency diagnosis of acute stroke.

Methods

We did a single-centre, prospective, blind comparison of non-contrast CT and MRI (with diffusion-weighted and susceptibility weighted images) in a consecutive series of patients referred for emergency assessment of suspected acute stroke. Scans were independently interpreted by four experts, who were unaware of clinical information, MRI-CT pairings, and follow-up imaging.

Results

356 patients, 217 of whom had a final clinical diagnosis of acute stroke, were assessed. MRI detected acute stroke (ischaemic or haemorrhagic), acute ischaemic stroke, and chronic haemorrhage more frequently than did CT (p<0·0001, for all comparisons). MRI was similar to CT for the detection of acute intracranial haemorrhage. MRI detected acute ischaemic stroke in 164 of 356 patients (46%; 95% CI 41–51%), compared with CT in 35 of 356 patients (10%; 7–14%). In the subset of patients scanned within 3 h of symptom onset, MRI detected acute ischaemic stroke in 41 of 90 patients (46%; 35–56%); CT in 6 of 90 (7%; 3–14%). Relative to the final clinical diagnosis, MRI had a sensitivity of 83% (181 of 217; 78–88%) and CT of 26% (56 of 217; 20–32%) for the diagnosis of any acute stroke.

Interpretation

MRI is better than CT for detection of acute ischaemia, and can detect acute and chronic haemorrhage; therefore it should be the preferred test for accurate diagnosis of patients with suspected acute stroke. Because our patient sample encompassed the range of disease that is likely to be encountered in emergency cases of suspected stroke, our results are directly applicable to clinical practice.

Introduction

Magnetic resonance imaging (MRI) is generally thought to be better than computed tomography (CT) for the diagnosis of acute stroke, but this belief has never been substantiated for the full range of patients in whom this diagnosis is suspected. Patients who present to the emergency room with stroke-like symptoms might have cerebrovascular disease (ischaemic or haemorrhagic) or various other non-vascular disorders. The ideal imaging modality for assessment of patients with acute stroke should accurately detect both cerebral ischaemia and intracranial haemorrhage, and discriminate cerebrovascular causes from other causes. CT is the most common imaging modality used to assess patients with suspected stroke. This method is widely available, fast, easy, and less expensive than MRI. However, although CT is sensitive to acute intracranial haemorrhage, it is not sensitive to acute ischaemic stroke. Studies suggest that CT is insufficiently sensitive for the diagnosis of acute ischaemia, is subject to substantial inter-rater variability in interpretation, and might not be better than MRI for detection of acute intracranial haemorrhage.1, 2, 3, 4

MRI offers advantages for the assessment of acute stroke. Changes of acute ischaemic injury are detectable sooner with MRI than with CT, especially with diffusion-weighted imaging, and ischaemic stroke diagnosis with MRI has greater interobserver and intraobserver reliability than CT, even in readers with little experience.5, 6, 7, 8 Historical concerns that MRI is not sufficiently sensitive to detect acute intracranial haemorrhage in the earliest hours from onset have been addressed by studies that show gradient-echo MRI is as accurate as CT in patients with focal stroke symptoms within 6 h of symptom onset.1, 3 However, the relative diagnostic yield of MRI and CT for routine emergency assessment of possible stroke, irrespective of time from onset, severity of symptoms, or ultimate diagnosis (cerebrovascular or otherwise), had not been investigated. We aimed to prospectively compare CT and MRI for the detection of acute stroke in the full range of patients who present for emergency assessment of stroke-like symptoms.

Section snippets

Study participants and clinical diagnosis

This study was a single-site, prospective comparison of CT and MRI for the assessment of acute stroke. It took place from Sept, 30, 2000, to Feb, 25, 2002, at Suburban Hospital, a community hospital in Bethesda, Maryland, USA, in accordance with the institutional review boards of both the hospital and the National Institute of Neurological Disorders and Stroke. A consecutive series of patients referred to the hospital's stroke team because of suspicion of acute stroke were eligible,

Results

Over 18 months, 450 patients were screened and 94 were excluded—49 because of MRI contraindications (ie, electronic implants, severe patient agitation or claustrophobia, or medical instability); 34 because CT was not obtained because of failure to follow protocol or because treatment was initiated immediately after MRI; and 11 because CT was uninterpretable (ie, severe patient movement or failure to save scans). All MRIs were judged adequate for the panel of readers to make an interpretation of

Discussion

We report that MRI is more effective than CT for the diagnosis of acute stroke in a typical patient sample. Our sample was representative of the range of patients who are likely to present with a clinical suspicion of acute stroke, including patients who ultimately proved to have a different diagnosis. Therefore, our results are directly applicable to clinical practice.

The earliest comparisons of MRI to CT in the diagnosis of acute stroke, from the early 1990s, before clinical

References (29)

  • AM Nor et al.

    The Recognition of Stroke in the Emergency Room (ROSIER) scale: development and validation of a stroke recognition instrument

    Lancet Neurol

    (2005)
  • PM Rothwell et al.

    A simple score (ABCD) to identify individuals at high early risk of stroke after transient ischaemic attack

    Lancet

    (2005)
  • JB Fiebach et al.

    Stroke magnetic resonance imaging is accurate in hyperacute intracerebral hemorrhage: a multicenter study on the validity of stroke imaging

    Stroke

    (2004)
  • JC Grotta et al.

    Agreement and variability in the interpretation of early CT changes in stroke patients qualifying for intravenous rtPA therapy

    Stroke

    (1999)
  • CS Kidwell et al.

    Comparison of MRI and CT for detection of acute intracerebral hemorrhage

    JAMA

    (2004)
  • JM Wardlaw et al.

    Early signs of brain infarction at CT: observer reliability and outcome after thrombolytic treatment—systematic review

    Radiology

    (2005)
  • S Warach et al.

    Acute human stroke studied by whole brain echo planar diffusion-weighted magnetic resonance imaging

    Ann Neurol

    (1995)
  • JP Mohr et al.

    Magnetic resonance versus computed tomographic imaging in acute stroke

    Stroke

    (1995)
  • RN Bryan et al.

    Diagnosis of acute cerebral infarction: comparison of CT and MR imaging

    AJNR Am J Neuroradiol

    (1991)
  • JB Fiebach et al.

    CT and diffusion-weighted MR imaging in randomized order: diffusion-weighted imaging results in higher accuracy and lower interrater variability in the diagnosis of hyperacute ischemic stroke

    Stroke

    (2002)
  • S Warach et al.

    Fast magnetic resonance diffusion-weighted imaging of acute human stroke

    Neurology

    (1992)
  • RG Gonzalez et al.

    Diffusion-weighted MR imaging: diagnostic accuracy in patients imaged within 6 hours of stroke symptom onset

    Radiology

    (1999)
  • PJ Kelly et al.

    Diffusion MRI in ischemic stroke compared to pathologically verified infarction

    Neurology

    (2001)
  • MG Lansberg et al.

    Comparison of diffusion-weighted MRI and CT in acute stroke

    Neurology

    (2000)
  • Cited by (962)

    View all citing articles on Scopus
    View full text