title: Standardized time to peak in ischemic and regular cerebral tissue measured with perfusion MR imaging.
abstract: OBJECTIVE
  Standardized time to peak (stdTTP) enables a quick quantification of time to peak measurements. An stdTTP </=3.5 seconds is reported to be regular, and evidence suggests that an stdTTP >/=7 seconds indicates critically perfused tissue. We verified this stdTTP in acute ischemia (within the first 6 hours after the onset of symptoms), when perfusion is critical, and after 24-72 hours.
  
  
  METHODS
  Combined diffusion-weighted imaging (DWI) and perfusion MR imaging was performed in 20 consecutive patients with acute cerebral ischemia. Distributions of stdTTP >/=7 and </=3.5 seconds were analyzed in corresponding regions with (ischemic injury) or without (no ischemic injury) substantial hyperintensity on DWI in both hemispheres. Follow-up examinations were available in 11 patients.
  
  
  RESULTS
  About 80% of voxels in regions with ischemic injury showed an stdTTP >/=7 seconds. StdTTP of about 80% of voxels was </=3.5 seconds in regions without ischemic injury. In both conditions, 14% of stdTTP values were between 3.5 and 7 seconds. We found a strong correlation between areas with stdTTP >/=7 seconds and resulting infarct (r(2)=0.86).
  
  
  CONCLUSIONS
  StdTTP is reciprocal in regions with and without ischemic injury. An stdTTP >/=7 seconds (regular range) is strongly correlated with resulting infarct and reflects critical perfusion with a high probability of ischemic tissue injury in acute ischemia, whereas this is unlikely in regions with stdTTP </=3.5 seconds (regular range). An stdTTP of 3.5-7 seconds is equivocal concerning ischemic injury and may indicate a tolerable perfusion condition.
authors.affiliation: Division of Neuroradiology, Department of Radiology, University of Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Nasel
authors.forename: Nicole
authors.initials: N
authors.lastname: Kronsteiner
authors.forename: Erwin
authors.initials: E
authors.lastname: Schindler
authors.forename: Sören
authors.initials: S
authors.lastname: Kreuzer
authors.forename: Stephan
authors.initials: S
authors.lastname: Gentzsch
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002545:Brain Ischemia / Q000473:pathology*; D002560:Cerebrovascular Circulation; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013997:Time Factors