title: Diffusion-weighted MRI in acute stroke within the first 6 hours: 1.5 or 3.0 Tesla?
abstract: OBJECTIVE
  To compare the sensitivity and specificity of 1.5-T and 3.0-T diffusion-weighted MRI (DWI) to detect hyperacute ischemic stroke lesions.
  
  
  METHODS
  We blindly reviewed the DWI of 135 acute stroke patients and 34 controls performed at 1.5 T (n = 108) or 3.0 T (n = 61). The stroke patients all had subsequently proved carotid territory ischemic stroke and were imaged within the first 6 hours after stroke onset. Four readers (2 neuroradiologists and 2 stroke neurologists) blinded to clinical data and magnetic field strength recorded the presence of ischemic lesions on DWI and apparent diffusion coefficient (ADC) maps if necessary. Sensitivity, specificity, and false-negative rates were computed. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and DWI contrasts were calculated at both field strengths.
  
  
  RESULTS
  The accuracy of DWI in stroke diagnosis was superior at 1.5 T (98.8%) than at 3.0 T (90.9%, p = 0.03). The sensitivity decreased from 99.1% at 1.5 T to 92.5% at 3.0 T (p = 0.06) and the specificity from 97.8% to 84.1% (p = 0.002). ADC map readings did not improve accuracy, sensitivity, or specificity. The false-negative rate was 0.6% at 1.5 T and 6.1% at 3.0 T. Type of readers, stroke severity, and type of the coil did not affect diagnosis value. SNR and CNR were significantly higher at 3 T (p < 0.0001) but DWI contrast was lower (p = 0.04).
  
  
  CONCLUSIONS
  Blind reading by 4 experts of a large series of images shows that 1.5-T diffusion-weighted MRI (DWI) is better than 3.0-T DWI for the imaging of hyperacute stroke during the therapeutic window of thrombolysis.
authors.affiliation: AP-HP, Urgences Cérébro-Vasculaires, Université Pierre et Marie Curie, Paris VI, Hôpital Pitié-Salpêtrière, Paris, France. charlotte.rosso@gmail.com
authors.forename: C
authors.initials: C
authors.lastname: Rosso
authors.forename: A
authors.initials: A
authors.lastname: Drier
authors.forename: D
authors.initials: D
authors.lastname: Lacroix
authors.forename: G
authors.initials: G
authors.lastname: Mutlu
authors.forename: C
authors.initials: C
authors.lastname: Pires
authors.forename: S
authors.initials: S
authors.lastname: Lehéricy
authors.forename: Y
authors.initials: Y
authors.lastname: Samson
authors.forename: D
authors.initials: D
authors.lastname: Dormont
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods* / Q000592:standards*; D006801:Humans; D008875:Middle Aged; D011446:Prospective Studies; D012189:Retrospective Studies; D020521:Stroke / Q000175:diagnosis* / Q000628:therapy; D013997:Time Factors