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(Stroke. 2003;34:e215.)
© 2003 American Heart Association, Inc.

Letters to the Editor

PWI/DWI Mismatch: Better Definition Required

Royal Melbourne Hospital, and University of Melbourne, Melbourne, Australia

Geoffrey Donnan, MD, FRACP

Austin Repatriation and Medical Centre, and University of Melbourne, Melbourne, Australia

An extract of the first 250 words of the full text is provided, because this article has no abstract.

To the Editor:

In their recent study of perfusion-weighted (PWI) and diffusion-weighted (DWI) image analysis, Coutts et al¹ have demonstrated the difficulties associated with interpretation of postprocessed perfusion maps. There are, however, more fundamental problems than PWI map interpretation in identifying patients with perfusion-diffusion mismatch. The first is a lack of consensus concerning the definition of mismatch. Although a PWI abnormality that is 20% larger than the volume of the isotropic DWI lesion is often taken to represent significant mismatch, this is somewhat arbitrary.² Furthermore, it has not been determined which PWI measure best defines the region of abnormal blood flow. Although most imaging groups have accepted that an index from the time domain is the most accurate, there is no agreement as to which is superior, ie, time to peak (TTP), Tmax (deconvolved TTP), or mean transit time (MTT) maps (Figure). In addition, the mathematical techniques used to estimate the true contrast transit times vary between groups.

View larger version (76K): [in this window] [in a new window]   The perfusion-weighted image (PWI) is a mean transit time (MTT) map. The hyperintense pixels demonstrate prolongation of MTT consistent with hypoperfusion in the right hemisphere. The diffusion-weighted image (DWI) demonstrates an area of acute bioenergetic compromise in the right hemisphere, which has a smaller volume than the abnormal MTT region (PWI-DWI mismatch). Normalization of the MTT map to the contralateral hemisphere +4 seconds results in a smaller PWI volume and mismatch is no longer present.

To make the definition of perfusion deficits more objective, threshold techniques can be used.³ In . . . [Full Text of this Article]

Shelagh B. Coutts, MBChB; Jessica E. Simon, MBChB Andrew M. Demchuk, MD

Seaman Family MR Research Centre, Foothills Medical Centre, Calgary Health Region and, Department of Clinical Neurosciences, University of Calgary, Calgary, Alberta, Canada

Richard Frayne, PhD J. Ross Mitchell, PhD

Seaman Family MR Research Centre, Foothills Medical Centre, Calgary Health Region and, Departments of Clinical Neurosciences and Radiology, University of Calgary, Calgary, Alberta, Canada

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