title: Physiological noise in MR images: an indicator of the tissue response to ischemia?
abstract: OBJECTIVE
  To determine whether measuring signal intensity (SI) fluctuations in MRI time series data from acute stroke patients would identify ischemic tissue.
  
  
  METHODS
  Prebolus perfusion-weighted MRI data from 32 acute ischemic stroke patients (N = 32) was analyzed as a time series. Ischemic and normal tissue regions were outlined and compared.
  
  
  RESULTS
  The magnitude of the measured SI fluctuations was significantly lower in ischemic regions relative to normal tissue. Spatial differences in these fluctuations occurred in a manner that was different than other perfusion-based metrics.
  
  
  CONCLUSIONS
  Prior studies have shown that SI fluctuations in MRI time series data correspond to the presence of physiological "noise," which includes vasomotion, an autoregulatory phenomenon that affects the tissue response to ischemia. In this study, SI fluctuations were found to decrease in ischemia, consistent with the notion that small vessels will remain open (fluctuations in vessel diameter will decrease) when there is a challenge to flow. Spatial variation in SI fluctuations appeared to be different from spatial variation seen on other perfusion-based metrics, suggesting that a separate contrast mechanism is responsible, one that might be of diagnostic and prognostic value in acute stroke in which the ability of tissue to withstand ischemia is currently not well visualized.
authors.affiliation: Medical Engineering Medical Physics Program, Division of Health Sciences and Technology, Harvard University-Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Harris H
authors.initials: HH
authors.lastname: Wang
authors.forename: Nina M
authors.initials: NM
authors.lastname: Menezes
authors.forename: Ming Wang
authors.initials: MW
authors.lastname: Zhu
authors.forename: Hakan
authors.initials: H
authors.lastname: Ay
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koroshetz
authors.forename: Hannu J
authors.initials: HJ
authors.lastname: Aronen
authors.forename: Jari O
authors.initials: JO
authors.lastname: Karonen
authors.forename: Yawu
authors.initials: Y
authors.lastname: Liu
authors.forename: Juho
authors.initials: J
authors.lastname: Nuutinen
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Wald
authors.forename: A Gregory
authors.initials: AG
authors.lastname: Sorensen
mesh_terms: D000368:Aged; D001921:Brain / Q000473:pathology*; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D018810:Magnetic Resonance Angiography; D008297:Male; D020521:Stroke / Q000175:diagnosis* / Q000503:physiopathology; D014666:Vasomotor System / Q000503:physiopathology