title: Local relationships between restricted water diffusion and oxygen consumption in the ischemic human brain.
abstract: OBJECTIVE
  MR is widely used to depict still ischemic but viable tissue in acute stroke. However, the relationship between the apparent diffusion coefficient (ADC) and energy failure from reduced oxygen supply are unknown in man.
  
  
  METHODS
  Acute carotid-territory stroke patients were studied prospectively with both diffusion tensor-imaging and back-to-back steady-state 15O-PET. Substantial numbers of voxels with oxygen extraction fraction >0.70 (ie, significant ongoing hypoxia) were identified in 3 patients (imaged at 7, 16 and 21 hours after stroke onset). In this voxel population, the quantitative relationships between the ADC and cerebral metabolic rate of oxygen (CMRO2), and ADC and cerebral blood flow (CBF), were assessed.
  
  
  RESULTS
  The ADC remained essentially unchanged until CBF reached values approximately 20 mls/100g per min, beyond which it declined linearly. In contrast, except when severely reduced, the ADC was a poorer predictor of CMRO2. For both CBF and CMRO2, however, the relationship with ADC became steeper with longer times since onset, ie, the same ADC reflected lower perfusion and CMRO2 with elapsed time.
  
  
  CONCLUSIONS
  Despite the small sample and late times from stroke onset, the findings indicate that the degree of restricted water diffusion reliably reflects the severity of oxygen deprivation below the penumbral threshold but is less strongly related to metabolic disruption, which may explain why the ADC does not reliably predict tissue outcome. However, the same degree of diffusion restriction may correspond to greater severity of tissue disruption with elapsing time, which has relevance for stroke therapy. Time elapsed since stroke onset should be taken into account when interpreting ADC declines and in voxel-based infarct prediction models.
authors.affiliation: Department of Clinical Neurosciences, University of Cambridge, UK.
authors.forename: Joseph V
authors.initials: JV
authors.lastname: Guadagno
authors.forename: P Simon
authors.initials: PS
authors.lastname: Jones
authors.forename: Tim D
authors.initials: TD
authors.lastname: Fryer
authors.forename: Olivier
authors.initials: O
authors.lastname: Barret
authors.forename: Franklin I
authors.initials: FI
authors.lastname: Aigbirhio
authors.forename: T Adrian
authors.initials: TA
authors.lastname: Carpenter
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Price
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Gillard
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Warburton
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Baron
mesh_terms: D000369:Aged, 80 and over; D001834:Body Water / Q000378:metabolism*; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism*; D002545:Brain Ischemia / Q000000981:diagnostic imaging / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D020215:Carotid Artery, Internal, Dissection / Q000150:complications; D002560:Cerebrovascular Circulation; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D002534:Hypoxia, Brain / Q000209:etiology* / Q000503:physiopathology; D020766:Intracranial Embolism / Q000150:complications; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D049268:Positron-Emission Tomography; D011446:Prospective Studies; D013997:Time Factors; D017585:Ultrasonography, Doppler, Transcranial