Published Online
on December 24, 2008

A more recent version of this article appeared on February 1, 2009

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Submitted on May 28, 2008
Revised on June 26, 2008
Accepted on July 18, 2008

Optimal Tmax Threshold for Predicting Penumbral Tissue in Acute Stroke

Jean-Marc Olivot MD, PhD^*; Michael Mlynash MD, MS; Vincent N. Thijs MD, PhD; Stephanie Kemp BS; Maarten G. Lansberg MD, PhD; Lawrence Wechsler MD; Roland Bammer PhD; Michael P. Marks MD; and Gregory W. Albers MD

From the Department of Neurology and Neurological Sciences and the Stanford Stroke Center (J.-M.O., M.M., S.K., M.G.L., G.W.A.), Stanford University Medical Center, Stanford Calif; the Department of Neurology, University Hospitals Leuven, and the Vesalius Research Center, VIB (V.N.T.), Leuven, Belgium; the UMPC Stroke Institute and Department of Neurology (L.W.), University of Pittsburgh, Pittsburgh, Pa; and the Department of Radiology and the Stanford Stroke Center (R.B., M.P.M.), Stanford University Medical Center, Stanford Calif.

^* To whom correspondence should be addressed. E-mail: jmolivot{at}stanford.edu.

Background and Purpose—We sought to assess whether the volume of the ischemic penumbra can be estimated more accurately by altering the threshold selected for defining perfusion-weighting imaging (PWI) lesions.

Methods—DEFUSE is a multicenter study in which consecutive acute stroke patients were treated with intravenous tissue-type plasminogen activator 3 to 6 hours after stroke onset. Magnetic resonance imaging scans were obtained before, 3 to 6 hours after, and 30 days after treatment. Baseline and posttreatment PWI volumes were defined according to increasing Tmax delay thresholds (>2, >4, >6, and >8 seconds). Penumbra salvage was defined as the difference between the baseline PWI lesion and the final infarct volume (30-day fluid-attenuated inversion recovery sequence). We hypothesized that the optimal PWI threshold would provide the strongest correlations between penumbra salvage volumes and various clinical and imaging-based outcomes.

Results—Thirty-three patients met the inclusion criteria. The correlation between infarct growth and penumbra salvage volume was significantly better for PWI lesions defined by Tmax >6 seconds versus Tmax >2 seconds, as was the difference in median penumbra salvage volume in patients with a favorable versus an unfavorable clinical response. Among patients who did not experience early reperfusion, the Tmax >4 seconds threshold provided a more accurate prediction of final infarct volume than the >2 seconds threshold.

Conclusions—Defining PWI lesions based on a stricter Tmax threshold than the standard >2 seconds delay appears to provide more a reliable estimate of the volume of the ischemic penumbra in stroke patients imaged between 3 and 6 hours after symptom onset. A threshold between 4 and 6 seconds appears optimal for early identification of critically hypoperfused tissue.

Key words: magnetic resonance imaging • perfusion-weighted imaging • acute brain infarct • thrombolysis

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