Oxygen Extraction Fraction on Baseline MRI Predicts Infarction Growth in Successfully Reperfused Patients

In patients with acute ischemic stroke, infarct growth occurs despite successful reperfusion. Oxygen extraction fraction (OEF) has shown promising results in evaluating ischemic tissue viability and can now be quantified from routinely performed dynamic susceptibility contrast perfusion. We aimed to determine the association of OEF alterations within the ischemic tissue on pretreatment magnetic resonance imaging and infarct growth in patients who underwent successful reperfusion.

In this retrospective cohort study from the University of California, Los Angeles, between 2015 and 2020, patients were included if they had anterior circulation large vessel occlusion, achieved successful reperfusion (Thrombolysis in Cerebral Infarction ≥2b), had pretreatment dynamic susceptibility contrast perfusion and posttreatment magnetic resonance imaging within 48 hours from reperfusion. Dynamic susceptibility contrast-derived OEF values were quantified from the segmented ischemic core (apparent diffusion coefficient ≤620×10^-6 mm²/s) and penumbra tissue (time-to-maximum [Tmax] >6 s) on pretreatment magnetic resonance imaging and normalized to contralateral hemisphere (relative oxygen extraction fraction [OEF_r]). Primary outcome was substantial infarct growth ≥10 mL, and secondary outcomes were continuous measures of infarct growth volume and penumbra-to-infarct conversion ratio. The associations between baseline clinical and imaging variables, including OEF_r and outcome measures, were tested by multivariate and regression analysis.

Among 89 patients who met inclusion criteria, 33 (37%) patients had infarct growth ≥10 mL. Patients with infarct growth had significantly (P<0.0001) lower penumbra-OEF_r values compared with those without infarct growth. There was significant association between penumbra OEF_r and infarct growth (β=-2.9 [95% CI, -5.0 to -0.8]; P=0.007) and similarly for penumbra-to-infarct conversion ratio (β=-10.4 [95% CI, -19.6 to -1.2]; P=0.028).

Our results showed penumbra-OEF_r is a promising imaging biomarker for predicting infarct growth in acute ischemic stroke following successful reperfusion. Although elevation of penumbra-OEF_r is protective, patients with lower penumbra-OEF_r values sustained further ischemic injury and infarct growth.