Optimal Tmax threshold for predicting penumbral tissue in acute stroke

Abstract

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.

Figure 1

Flow chart for the study.

Figure 2

Illustration of the evolution of PWI lesion volumes according to Tmax delay. The patient, a 79-year-old woman, was treated with intravenous tPA 340 minutes after symptom onset. She did not experience an FCR. Baseline MRI was performed 302 minutes after symptom onset; the first follow-up MRI was 270 minutes after the start of treatment, and the final MRI was 27 days after symptom onset. Tmax color scale: 2 secondsTmax≤8 seconds (yellow); 8 seconds>Tmax (red). A, On baseline DWI, lesion volume was 15 cm³. B, On baseline PWI, lesion volumes according to Tmax delay were as follows: Tmax >2 seconds=67 cm³; >4 seconds, 34 cm³; >6 seconds, 12 cm³; and >8 seconds, 9 cm³.C,On follow-up PWI, lesion volumes according to Tmax delay were as follows: >2 seconds, 97 cm³; >4 seconds, 57 cm³; >6 seconds, 17 cm³; and >8 seconds, 13 cm³. D, On final FLAIR, final infarct volume was 24 cm³.