ABSTRACT NUMBER: ESOC2026A2093 PENUMBRA BASED OXYGEN EXTRACTION FRACTION (OEF) IN ACUTE STROKE DETECTED WITH MRI

Abstract Background and aims The reliability of quantitative perfusion-weighted MRI derived maps is still controversial. We assessed the validity of PWI-parameters using oxygen-extraction-fraction (OEF) measurements obtained with quantitative 15O-water-PET as a reference for identifying tissue with increased OEF (penumbra). Methods PW-MRI was acquired on a 1.5 Tesla system using a 3D EPI-PRESTO protocol, while OEF-PET imaging was performed on an ECAT-EXACT-HR-scanner (Siemens/CTI). In patients with acute and subacute ischemic stroke, maps of rCBF, rCBV, rMTT, rTTP and Tmax were compared with OEF-PET images. Regions of interest were positioned over cortical areas of the affected hemisphere and classified according to PET-derived OEF-values. Receiver-operating-characteristic (ROC) analysis was applied to evaluate the ability of PWI-parameters to identify penumbral tissue, using quantitative OEF-PET as the reference. Optimal PWI thresholds for detecting elevated OEF (>150% of the contralateral hemisphere) were determined. Results Pooled data from six stroke patients (median MRI-PET interval: 66 minutes; imaging performed within 17 hours of symptom onset) showed the following optimal thresholds (sensitivity and specificity): rCBF 0.49 (79% and 78%), rCBV 0.69 (61% and 61%), rMTT 2.7 (71% and 77%), rTTP 4.7 (79% and 80%) and Tmax 5.5 (82% and 83%). Among all parameters, rTTP and Tmax demonstrated the highest accuracy for identifying regions with increased OEF consistent with penumbra. Conclusions Of the frequently applied PWI-derived maps, Tmax provided the most accurate estimation of penumbral tissue, achieving sensitivities and specificities above 80%. TTP maps generated without arterial-input-function (AIF) correction performed comparably to deconvolution-based parameters such as CBF and MTT that require AIF determination. Conflict of interest Olivier Zaro-Weber: nothing to disclose