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 (Ͼ2, Ͼ4, Ͼ6, and Ͼ8 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 Ͼ6 seconds versus Tmax Ͼ2 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 Ͼ4 seconds threshold provided a more accurate prediction of final infarct volume than the Ͼ2 seconds threshold. Conclusions-Defining PWI lesions based on a stricter Tmax threshold than the standard Ͼ2 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.

Perfusion-Weighted Imaging–Derived Collateral Flow Index is a Predictor of MCA M1 Recanalization after IV Thrombolysis

“…This index of collateral circulation deficit is based on the ratio of volume of critically hypoperfused area (absolute Tmax value Ͼ6 seconds 13,14 in the current study) over the volume of moderately hypoperfused area (absolute Tmax value between 2 and 6 seconds in the current study), which was proposed by Bang et al 6 for quantifying the severity of brain perfusion defects. Indeed, although these authors used a lower critical Tmax threshold (4 seconds), this ratio was significantly correlated with angiographic collateral grading in patients with MCA occlusion.…”

Use of Magnetic Resonance Imaging to Predict Outcome after Stroke: A Review of Experimental and Clinical Evidence

“…Notably, MRI prediction was better in patients without reperfusion, indicating that, probably because of interindividual variance, perfusion thresholds might be even more difficult to determine on the verge of recanalization. In a different study, DSC perfusion maps were predictive of favorable clinical outcome to rtPA treatment when increasing the threshold for the delay of the time-to-peak residue function (T max ) (Olivot et al, 2009).…”

Performance and Predictive Value of a User-Independent Platform for CT Perfusion Analysis: Threshold-Derived Automated Systems Outperform Examiner-Driven Approaches in Outcome Prediction of Acute Ischemic Stroke

“…Heterogeneity in reperfusion of the study population precludes conclusive judgments as to a singular, ideal Tmax threshold for outcome prediction, for which past reports have documented variability in performance between a 4-and 6-second delay, depending on reperfusion status, in line with the best performing Tmax thresholds above. 6 NCCT-ASPECTS, while providing a rapid algorithm for determination of the extent of infarcted tissues, may have insensitivity to infarction in the early stages of injury, before the bulk water shift detection on noncontrast imaging. 10,12,14,20 We suspect that the clustering of abnormal brain regions in ASPECTS methodology, while providing for some uniformity in analysis, may have further limited the dynamic range for discriminating between lesions with similar ASPECTS but differing in actual extent or size.…”

“…1,3 Despite promising results, penumbral imaging has met with skepticism and inconsistent outcomes, particularly because the broad array of imaging and computational approaches and interpretive parameters has precluded formulation of generalizable conclusions. [4][5][6][7] With studies further complicated by the time, materials, and expertise requisite to successfully undertake perfusion imaging, some investigators have focused on triage algorithms examining more readily attainable biomarkers derived from noncontrast CT (eg, Alberta Stroke Program Early CT Score) or CT angiography (eg, collateral score [CS], clot burden score [CBS]) common to stroke protocols. [8][9][10][11] While quickly attainable, the performance of ASPECTS in triaging patients to therapy or predicting outcome has been variable, and its use in prognostication of individual outcomes has been questioned.…”