title: MR diffusion and perfusion parameters: relationship to metabolites in acute ischaemic stroke.
abstract: BACKGROUND
  Magnetic resonance (MR) diffusion and perfusion imaging are used to identify ischaemic penumbra, but there are few comparisons with neuronal loss and ischaemia in vivo. The authors compared N-acetyl aspartate (NAA, found in intact neurons) and lactate (anaerobic metabolism) with diffusion/perfusion parameters.
  
  
  METHODS
  The authors prospectively recruited patients with acute ischaemic stroke and performed MR diffusion tensor, perfusion (PWI) and proton chemical shift spectroscopic imaging (CSI). We superimposed a 0.5 cm voxel grid on the diffusion-weighted images (DWI) and classified voxels as 'definitely abnormal,' 'possibly abnormal' or normal on DWI appearance, and 'mismatch' for voxels in DWI/PWI mismatch areas. The authors compared metabolite (NAA, lactate), perfusion and apparent diffusion coefficient (ADC) values in each voxel type.
  
  
  RESULTS
  NAA differentiated 'definitely' from 'possibly abnormal,' and 'possibly abnormal' from 'mismatch' (both comparisons p<0.01) voxels, but not 'mismatch' from 'normal' voxels. Lactate was highest in 'definitely abnormal,' and progressively lower in 'possibly abnormal,' 'mismatch,' than 'normal' voxels (all differences p<0.01). There was no correlation between NAA and ADC or PWI values, but high lactate correlated with low ADC (Spearman r=-0.41, p=0.02) and prolonged mean transit time (Spearman r=0.42, p=0.02).
  
  
  CONCLUSIONS
  ADC and mean transit time indicate the presence of ischaemia (lactate) but not cumulative total neuronal damage (NAA) in acute ischaemic stroke, suggesting that caution is required if using ADC and PWI parameters to differentiate salvageable from non-salvageable tissue. Further refinement of the DWI/PWI concept is required prior to more widespread use.
authors.affiliation: SFC Brain Imaging Research Centre, SINAPSE Collaboration, Division of Clinical Neuroscience, Western General Hospital, Crewe Rd, Edinburgh EH4 2XU, UK. joanna.wardlaw@ed.ac.uk
authors.forename: Vera
authors.initials: V
authors.lastname: Cvoro
authors.forename: Ian
authors.initials: I
authors.lastname: Marshall
authors.forename: Paul A
authors.initials: PA
authors.lastname: Armitage
authors.forename: Mark E
authors.initials: ME
authors.lastname: Bastin
authors.forename: Trevor
authors.initials: T
authors.lastname: Carpenter
authors.forename: Carly S
authors.initials: CS
authors.lastname: Rivers
authors.forename: Martin S
authors.initials: MS
authors.lastname: Dennis
authors.forename: Joanna M
authors.initials: JM
authors.lastname: Wardlaw
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D001921:Brain / Q000098:blood supply*; D002545:Brain Ischemia / Q000175:diagnosis / Q000378:metabolism* / Q000503:physiopathology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012720:Severity of Illness Index
chemical_list: D001224:Aspartic Acid; D019344:Lactic Acid; C000179:N-acetylaspartate