title: CT perfusion mean transit time maps optimally distinguish benign oligemia from true "at-risk" ischemic penumbra, but thresholds vary by postprocessing technique.
abstract: OBJECTIVE
  Various CTP parameters have been used to identify ischemic penumbra. The purpose of this study was to determine the optimal CTP parameter and threshold to distinguish true "at-risk" penumbra from benign oligemia in acute stroke patients without reperfusion.
  
  
  METHODS
  Consecutive stroke patients were screened and 23 met the following criteria: 1) admission scanning within 9 hours of onset, 2) CTA confirmation of large vessel occlusion, 3) no late clinical or radiographic evidence of reperfusion, 4) no thrombolytic therapy, 5) DWI imaging within 3 hours of CTP, and 6) either CT or MR follow-up imaging. CTP was postprocessed with commercial software packages, using standard and delay-corrected deconvolution algorithms. Relative cerebral blood flow, volume, and mean transit time (rCBF, rCBV and rMTT) values were obtained by normalization to the uninvolved hemisphere. The admission DWI and final infarct were transposed onto the CTP maps and receiver operating characteristic curve analysis was performed to determine optimal thresholds for each perfusion parameter in defining penumbra destined to infarct.
  
  
  RESULTS
  Relative and absolute MTT identified penumbra destined to infarct more accurately than CBF or CBV*CBF (P < .01). Absolute and relative MTT thresholds for defining penumbra were 12s and 249% for the standard and 13.5s and 150% for the delay-corrected algorithms, respectively.
  
  
  CONCLUSIONS
  Appropriately thresholded absolute and relative MTT-CTP maps optimally distinguish "at-risk" penumbra from benign oligemia in acute stroke patients with large-vessel occlusion and no reperfusion. The precise threshold values may vary, however, depending on the postprocessing technique used for CTP map construction.
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114-9657, USA.
authors.forename: Shervin
authors.initials: S
authors.lastname: Kamalian
authors.forename: Shahmir
authors.initials: S
authors.lastname: Kamalian
authors.forename: A A
authors.initials: AA
authors.lastname: Konstas
authors.forename: M B
authors.initials: MB
authors.lastname: Maas
authors.forename: S
authors.initials: S
authors.lastname: Payabvash
authors.forename: S R
authors.initials: SR
authors.lastname: Pomerantz
authors.forename: P W
authors.initials: PW
authors.lastname: Schaefer
authors.forename: K L
authors.initials: KL
authors.lastname: Furie
authors.forename: R G
authors.initials: RG
authors.lastname: González
authors.forename: M H
authors.initials: MH
authors.lastname: Lev
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002545:Brain Ischemia / Q000150:complications* / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D055420:Perfusion Imaging / Q000379:methods*; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D020521:Stroke / Q000150:complications* / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*