title: Predicting infarction within the diffusion-weighted imaging lesion: does the mean transit time have added value?
abstract: OBJECTIVE
  There is ample evidence that in anterior circulation stroke, the diffusion-weighted imaging (DWI) lesion may escape infarction and thus is not a reliable infarct predictor. In this study, we assessed the predictive value of the mean transit time (MTT) for final infarction within the DWI lesion, first in patients scanned back-to-back with 15O-positron emission tomography and MR (DWI and perfusion-weighted imaging; "Cambridge sample") within 7 to 21 hours of clinical onset, then in a large sample of patients with anterior circulation stroke receiving DWI and perfusion-weighted imaging within 12 hours (85% within 6 hours; "I-KNOW sample").
  
  
  METHODS
  Both samples underwent structural MRI at approximately 1 month to map final infarcts. For both imaging modalities, MTT was calculated as cerebral blood volume/cerebral blood flow. After image coregistration and matrix resampling, the MTT values between voxels of interest that later infarcted or not were compared separately within and outside DWI lesions (DWI+ and DWI-, respectively) both within and across patients. In the I-KNOW sample, receiver operating characteristic curves were calculated for these voxel of interest populations and areas under the curve and optimal thresholds calculated.
  
  
  RESULTS
  In the Cambridge data set (n=4), there was good concordance between predictive values of MTT (positron emission tomography) and MTT (perfusion-weighted imaging) for both DWI+ and DWI- voxels of interest indicating adequate reliability of MTT (perfusion-weighted imaging) for this purpose. In the I-KNOW data set (N=42), the MTT significantly added to the DWI lesion to predict infarction in both DWI- and DWI+ voxels of interest with areas under the curve approximately 0.78 and 0.64 (both P<0.001) and optimal thresholds approximately 8 seconds and 11 seconds, respectively.
  
  
  CONCLUSIONS
  Despite the relatively small samples, this study suggests that adding MTT (perfusion-weighted imaging) may improve infarct prediction not only as already known outside, but also within, DWI lesions.
authors.affiliation: Department Clinical Neurosciences, Cambridge University, Cambridge, UK.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Carrera
authors.forename: P Simon
authors.initials: PS
authors.lastname: Jones
authors.forename: Josef A
authors.initials: JA
authors.lastname: Alawneh
authors.forename: Irene
authors.initials: I
authors.lastname: Klærke Mikkelsen
authors.forename: Tae-Hee
authors.initials: TH
authors.lastname: Cho
authors.forename: Suzanne
authors.initials: S
authors.lastname: Siemonsen
authors.forename: Joseph V
authors.initials: JV
authors.lastname: Guadagno
authors.forename: Kim
authors.initials: K
authors.lastname: Mouridsen
authors.forename: Lars
authors.initials: L
authors.lastname: Ribe
authors.forename: Niels
authors.initials: N
authors.lastname: Hjort
authors.forename: Tim D
authors.initials: TD
authors.lastname: Fryer
authors.forename: T Adrian
authors.initials: TA
authors.lastname: Carpenter
authors.forename: Franklin I
authors.initials: FI
authors.lastname: Aigbirhio
authors.forename: Jens
authors.initials: J
authors.lastname: Fiehler
authors.forename: Norbert
authors.initials: N
authors.lastname: Nighoghossian
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Warburton
authors.forename: Leif
authors.initials: L
authors.lastname: Ostergaard
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Baron
mesh_terms: D002544:Cerebral Infarction / Q000473:pathology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D011446:Prospective Studies; D012372:ROC Curve; D013997:Time Factors