title: Assessment of tissue viability using diffusion- and perfusion-weighted MRI in hyperacute stroke.
abstract: OBJECTIVE
  The aim of this study was to investigate the relationship between the diffusion and perfusion parameters in hyperacute infarction, and we wanted to determine the viability threshold for the ischemic penumbra using diffusion- and perfusion-weighted imaging (DWI and PWI, respectively).
  
  
  METHODS
  Both DWI and PWI were performed within six hours from the onset of symptoms for 12 patients who had suffered from acute stroke. Three regions of interest (ROIs) were identified: ROI 1 was the initial lesion on DWI; ROI 2 was the DWI/PWI mismatch area (the penumbra) that progressed onward to the infarct; and ROI 3 was the mismatch area that recovered to normal on the follow-up scans. The ratios of apparent diffusion coefficient (ADC), the relative cerebral blood volume (rCBV), and the time to peak (TTP) were calculated as the lesions' ROIs divided by the contralateral mirror ROIs, and these values were then correlated with each other. The viability threshold was determined by using the receiver operating characteristic (ROC) curves.
  
  
  RESULTS
  For all three ROIs, the ADC ratios had significant linear correlation with the TTP ratios (p < 0.001), but not with the rCBV ratios (p = 0.280). There was no significant difference for the ADC and rCBV ratios within the ROIs. The mean TTP ratio/TTP delay between the penumbras' two ROIs showed a significant statistical difference (p < 0.001). The cutoff value between ROI 2 and ROI 3, as the viability threshold, was a TTP ratio of 1.29 (with a sensitivity and specificity of 86% and 73%, respectively) and a TTP delay of 7.8 sec (with a sensitivity and specificity of 84% and 72%, respectively).
  
  
  CONCLUSIONS
  Determining the viability thresholds for the TTP ratio/delay on the PWI may be helpful for selecting those patients who would benefit from the various therapeutic interventions that can be used during the acute phase of ischemic stroke.
authors.affiliation: Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. wonjin.moon@samsung.com
authors.forename: Won-Jin
authors.initials: WJ
authors.lastname: Moon
authors.forename: Dong Gyu
authors.initials: DG
authors.lastname: Na
authors.forename: Jae Wook
authors.initials: JW
authors.lastname: Ryoo
authors.forename: Hong Gee
authors.initials: HG
authors.lastname: Roh
authors.forename: Hong Sik
authors.initials: HS
authors.lastname: Byun
authors.forename: Yong Hwan
authors.initials: YH
authors.lastname: Chon
authors.forename: Eun Chul
authors.initials: EC
authors.lastname: Chung
mesh_terms: D000208:Acute Disease; D000368:Aged; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D020521:Stroke / Q000175:diagnosis*; D014022:Tissue Survival / Q000502:physiology*