title: Relative FLAIR Signal Intensities over Time in Acute Ischemic Stroke: Comparison of Two Methods.
abstract: OBJECTIVE
  Visibility of lesions on fluid attenuated inversion recovery (FLAIR) images appears indicative of the time window in acute ischemic stroke. We compared two published methods for calculation of relative FLAIR signal intensities (rSI) regarding their association with time from symptom onset in a longitudinal fashion.
  
  
  METHODS
  We prospectively included patients receiving serial MRI examinations between 4.5 and 35 hours from symptom onset. FLAIR rSI was determined using two methods: a whole regions-of-interest (ROI) method and a hotspot method, selecting only a single area of visually highest signal. Signal intensity (rSI) was calculated relative to the contralateral side for each time point.
  
  
  RESULTS
  We included 21 patients with 3-6 MRI examinations on the first 2 days after stroke onset. FLAIR rSI determined with both methods shows a linear association with time from onset, although the hotspot results showed higher variability. Both methods with their previously published thresholds are reliable for identifying patients outside the 4.5 hours time window.
  
  
  CONCLUSIONS
  Both methods show a similar performance, and might be a suitable help for the visual assessment of FLAIR lesion visibility.
authors: Center for Stroke Research Berlin (CSB), Charité Universitätsmedizin Berlin, Germany.
authors: Ann-Christin
authors: AC
authors: Ostwaldt
authors: Center for Stroke Research Berlin (CSB), Charité Universitätsmedizin Berlin, Germany.
authors: Ivana
authors: I
authors: Galinovic
authors: Center for Stroke Research Berlin (CSB), Charité Universitätsmedizin Berlin, Germany.
authors: Benjamin
authors: B
authors: Hotter
authors: Center for Stroke Research Berlin (CSB), Charité Universitätsmedizin Berlin, Germany.|Department for Biostatistics and Clinical Epidemiology, Charité Universitätsmedizin Berlin, Germany.
authors: Ulrike
authors: U
authors: Grittner
authors: Center for Stroke Research Berlin (CSB), Charité Universitätsmedizin Berlin, Germany.|Department of Neurology, Charité Universitätsmedizin Berlin, Germany.
authors: Christian H
authors: CH
authors: Nolte
authors: Center for Stroke Research Berlin (CSB), Charité Universitätsmedizin Berlin, Germany.|Department of Neurology, Charité Universitätsmedizin Berlin, Germany.
authors: Heinrich J
authors: HJ
authors: Audebert
authors: Center for Stroke Research Berlin (CSB), Charité Universitätsmedizin Berlin, Germany.
authors: Kersten
authors: K
authors: Villringer
authors: Center for Stroke Research Berlin (CSB), Charité Universitätsmedizin Berlin, Germany.
authors: Jochen B
authors: JB
authors: Fiebach
mesh_terms: D000368:Aged; D001921:Brain / Q000000981:diagnostic imaging*; D002545:Brain Ischemia / Q000000981:diagnostic imaging*; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020521:Stroke / Q000000981:diagnostic imaging*; D013997:Time Factors
keywords: FLAIR; Magnetic resonance imaging; acute ischemic stroke; time course