Abstract 12: MR-Oxygen Metabolic Index (OMI) is Superior To Diffusion-Perfusion Mismatch For Predicting Tissue Fate in the Ischemic Penumbra

Abstract

Background: MR oxygen metabolic index (OMI) is an MR approach closely related to PET-CMRO 2 . We directly compared infarct probabilities in predicted penumbral tissue defined by OMI to that of diffusion-perfusion mismatch (DPM) in a cohort of acute stroke patients. Methods: 38 acute ischemic stroke patients were imaged at 3.0 hr (tp1), 6.2 hr (tp2), and 1 month (tp3) after onset. Dynamic susceptibility contrast and asymmetry spin echo measured CBF and OEF, respectively. OMI=CBFxOEF. Co-registered voxels were normalized to the non-ischemic hemisphere. OMI- and DPM-derived thresholds (for core/penumbra and penumbra/oligemia) were directly compared by examining infarct probabilities (IP) in 4 tissue categories subdivided by reperfusion status: (1) tissue that died regardless of reperfusion ( core ); (2) tissue that died without reperfusion ( penumbra_non-reperfused ); (3) tissue that survived with reperfusion ( penumbra_reperfused ); and (4) tissue that survived regardless of reperfusion ( oligemia ). “Average prediction error” (APE), a metric combining the differences for each tissue group’s predicted IP from the ideal IP (Table). The predictive abilities of OMI- vs. DPM thresholds were applied to each patient and the IP for each of the 4 tissue groups was calculated and averaged across the population, and compared using Wilcoxon signed rank test. Previously determined OMI thresholds were 0.22 and 0.42 relative to the non-ischemic hemisphere; DPM thresholds were based on DEFUSE-2 criteria [core=ADC<600mm 2 /s, Tmax>6s; penumbra=ADC >600mm 2 /s, Tmax>6s; oligemia=ADC>600mm 2 /s, Tmax<6s]. Results: Infarct probabilities for OMI and DPM are shown (Table): IP penumbra_non-reperfused was higher with OMI compared to DPM (74% vs. 56%, p<0.0001), while IPs in the other 3 tissue groups did not differ. APE was significantly lower for OMI than for DPM (15% vs. 22%, p=0.03). Conclusions: OMI thresholds predict reperfusion-dependent tissue outcome in the penumbra better than DPM.