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(Stroke. 2009;40:767.)
© 2009 American Heart Association, Inc.

Original Contributions

Associations Between Diffusion and Perfusion Parameters, N-Acetyl Aspartate, and Lactate in Acute Ischemic Stroke

Vera Cvoro, MRCP; Joanna M. Wardlaw, MD, FRCR, FRCP, FMedSci; Ian Marshall, PhD; Paul A. Armitage, PhD; Carly S. Rivers, PhD; Mark E. Bastin, DPhil; Trevor K. Carpenter, PhD; Karolina Wartolowska, MD; Andrew J. Farrall, BSc, MSc, MD, FRCPC Martin S. Dennis, MD, FRCP (ed)

From the Divisions of Clinical Neurosciences (V.C., J.M.W., P.A.A., T.K.C., A.J.F., M.S.D.) and Medical Physics (I.M., M.E.B.), University of Edinburgh, Western General Hospital; Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (K.W.), University of Oxford; and Clinical Trials Research Unit (C.S.R.), University of Leeds, UK.

Correspondence to Prof Joanna M. Wardlaw, Division of Clinical Neurosciences, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU, UK. E-mail Joanna.wardlaw{at}ed.ac.uk

Background and Purpose— In acute ischemic stroke, the amount of neuronal damage in hyperintense areas on MR diffusion imaging (DWI) is unclear. We used spectroscopic imaging to measure N-acetyl aspartate (NAA, a marker of normal neurons) and lactate (a marker of ischemia) to compare with diffusion and perfusion values in the diffusion lesion in acute ischemic stroke.

Methods— We recruited patients with acute ischemic stroke prospectively and performed MR diffusion weighted (DWI), perfusion, and spectroscopic imaging. We coregistered the images, outlined the visible diffusion lesion, and extracted metabolite, perfusion, and apparent diffusion coefficient (ADC) values from the diffusion lesion.

Results— 42 patients were imaged, from 1.5 to 24 hours after stroke. In the DWI lesion, although NAA was reduced, there was no correlation between NAA and ADC or perfusion values. However, raised lactate correlated with reduced ADC (Spearman =0.32, P=0.04) and prolonged mean transit time (MTT, =0.31, P=0.04). Increasing DWI lesion size was associated with lower NAA and higher lactate (=–0.44, P=0.003; =0.49, P=0.001 respectively); NAA fell with increasing times to imaging (=–0.3, P=0.03), but lactate did not change.

Conclusion— Although larger confirmatory studies are needed, the correlation of ADC and MTT with lactate but not NAA suggests that ADC and MTT are better markers of the presence of ischemia than of cumulative neuronal loss. Further studies should define more precisely the rate of neuronal loss and relationship to diffusion and perfusion parameters with respect to the depth and duration of ischemia.

Key Words: stroke • spectroscopy • metabolites • N-acetyl aspartate • lactate • ADC • CSI • DWI • PWI