title: Regional ischemic vulnerability of the brain to hypoperfusion: the need for location specific computed tomography perfusion thresholds in acute stroke patients.
abstract: OBJECTIVE
  To characterize the spatial pattern of cerebral ischemic vulnerability to hypoperfusion in stroke patients.
  
  
  METHODS
  We included 90 patients who underwent admission CT perfusion and MRI within 12 hours of ischemic stroke onset. Infarcted brain lesions ("core") were segmented from admission diffusion-weighted imaging and, along with the CT perfusion parameter maps, coregistered onto MNI-152 brain space, which was parcellated into 125 mirror cortical and subcortical regions per hemisphere. We tested the hypothesis that the percent infarction increment per unit of relative cerebral blood flow (rCBF) reduction differs statistically between regions using regression analysis to assess the interaction between regional rCBF and region variables. Next, for each patient, a "vulnerability index" map was constructed with voxel values equaling the product of that voxel's rCBF and infarction probability (derived from the MNI-152-transformed, binary, segmented, diffusion-weighted imaging lesions). Voxel-based rCBF threshold for core was determined within the upper 20th percentile of vulnerability index map voxel values.
  
  
  RESULTS
  Different regions had different percent infarction increase per unit rCBF reduction (P=0.001). The caudate body, putamen, insular ribbon, paracentral lobule, and precentral, middle, and inferior frontal gyri had the highest ischemic vulnerability to hypoperfusion. A voxel-based rCBF threshold of <0.42 optimally distinguished infarct core in the highly-vulnerable regions, whereas rCBF<0.16 distinguished core in the remainder of the brain.
  
  
  CONCLUSIONS
  We demonstrated regional ischemic vulnerability of the brain to hypoperfusion in acute stroke patients. Location-specific, rather than whole-brain, rCBF thresholds may provide a more accurate metric for estimating infarct core using CT perfusion maps.
authors.affiliation: Massachusetts General Hospital and Harvard Medical School, Department of Radiology, Gray 241H, Boston, MA 02114-9657, USA.
authors.forename: Seyedmehdi
authors.initials: S
authors.lastname: Payabvash
authors.forename: Leticia C S
authors.initials: LC
authors.lastname: Souza
authors.forename: Yifei
authors.initials: Y
authors.lastname: Wang
authors.forename: Pamela W
authors.initials: PW
authors.lastname: Schaefer
authors.forename: Karen L
authors.initials: KL
authors.lastname: Furie
authors.forename: Elkan F
authors.initials: EF
authors.lastname: Halpern
authors.forename: R Gilberto
authors.initials: RG
authors.lastname: Gonzalez
authors.forename: Michael H
authors.initials: MH
authors.lastname: Lev
mesh_terms: D002545:Brain Ischemia / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000503:physiopathology; D002421:Caudate Nucleus / Q000098:blood supply / Q000000981:diagnostic imaging / Q000473:pathology; D002540:Cerebral Cortex / Q000098:blood supply / Q000000981:diagnostic imaging / Q000473:pathology; D002560:Cerebrovascular Circulation / Q000502:physiology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D010477:Perfusion; D011699:Putamen / Q000098:blood supply / Q000000981:diagnostic imaging / Q000473:pathology; D012189:Retrospective Studies; D012307:Risk Factors; D020521:Stroke / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000503:physiopathology; D014057:Tomography, X-Ray Computed / Q000379:methods*