Apparent Diffusion Coefficient Thresholds and Diffusion Lesion Volume in Acute Stroke Ralph G. R. Thomas, BSc, MRCP ,*† G. Katherine Lymer, CEng, CSci, MIET , MIPEM, PhD,*† Paul A. Armitage, PhD,*† Francesca M. Chappell, MSc, PhD,* Trevor Carpenter, PhD,*† Bartosz Karaszewski, MD, PhD,*†‡ Martin S. Dennis, MD, FRCP ,* and Joanna M. Wardlaw, FRCR, FRCP , MD, FMedSci*† Background: Apparent diffusion coefficient (ADC) thresholds are used to determine acute stroke lesion volume, but the reliability of this approach and comparability to the volume of the magnetic resonance diffusion-weighted imaging (MR-DWI) hyperintense lesion is unclear. Methods: We prospectively recruited and clinically assessed patients who had experienced acute ischemic stroke and performed DWI less than 24 hours and at 3 to 7 days after stroke. We compared the volume of the manually outlined DW hyperintense lesion (reference standard) with lesion vol- umes derived from 3 commonly used ADC thresholds: .55 3 10 23 /mm 2 /second 21 , .65 3 10 23 /mm 2 /second 21 , and .75 3 10 23 /mm 2 /second 21 , with and without ‘‘ed- iting’’ of erroneous tissue. We compared the volumes obtained by reference stan- dard, ‘‘raw,’’ and ‘‘edited’’ thresholds. Results: Among 33 representative patients, the acute DWI lesion volume was 15,284 mm 3 ; the median unedited/edited ADC volumes were 52,972/2786 mm 3 , 92,707/6,987 mm 3 , and 227,681/unmeasureable mm 3 (.55 3 10 23 /mm 2 /second 21 , .65 3 10 23 /mm 2 /second 21 , and .75 3 10 23 / mm 2 /second 21 thresholds, respectively). Subacute lesions gave similar differences. These differences between edited and unedited diffusion-weighted imaging and ADC volumes were statistically significant. Conclusions: Threshold-derived ADC volumes require substantial manual editing to avoid over- or underestimating the visible DWI lesion and should be used with caution. Key Words: Stroke— apparent diffusion coefficient—magnetic resonance imaging—threshold. Ó 2013 by National Stroke Association Magnetic resonance diffusion-weighted imaging (MR- DWI) shows acute ischemic lesions very soon after stroke. These can be quantified by tracing around the visible hyperintense DWI lesion to measure the vol- ume. 1 This is time consuming. Automated techniques could facilitate quantification of stroke lesion volume in research and clinical practice. 2 One method is to ‘‘threshold’’ the apparent diffusion coefficient (ADC) map, using a percentage of normal 3 or an absolute 4,5-7 ADC value, and record the resulting volume. The relationship between the DWI visible lesion volume and the ADC-thresholded volume, and which threshold From the *Brain Research Imaging Centre, Division of Clinical Neurosciences, University of Edinburgh, Western General Hospital, Edinburgh, Scotland, United Kingdom; †Scottish Imaging Network, A Platform for Scientific Collaboration (SINAPSE); and ‡Department of Adult Neurology, Medical University of Gdansk, Poland. Received August 2, 2012; revision received September 23, 2012; accepted September 30, 2012. This work was funded by a grant from The Stroke Association (Registered Charity SC037789), Project Ref No: TSA 2006/11. B.K. is supported by fellowships from the Foundation for Polish Science and the International Brain Research Organization (IBRO). P.A.A. is supported by the Row Fogo Charitable Trust. J.M.W. and G.K.L. are supported by the Scottish Funding Council through the Scottish Imaging Network, A Platform for Scientific Excellence (SINAPSE) Collaboration (www.sinapse.ac.uk). Address correspondence to Joanna M. Wardlaw, FRCR, FRCP, MD, FMedSci, Brain Research Imaging Centre, SINAPSE Collaboration, Division of Clinical Neurosciences, Western General Hospital, Crewe Rd, Edinburgh, EH4 2XU, UK. E-mail: joanna.wardlaw@ed.ac.uk. 1052-3057/$ - see front matter Ó 2013 by National Stroke Association http://dx.doi.org/10.1016/j.jstrokecerebrovasdis.2012.09.018 906 Journal of Stroke and Cerebrovascular Diseases, Vol. 22, No. 7 (October), 2013: pp 906-909