Oxygen extraction fraction changes in ischemic tissue from 24-72 hours to 12 months after successful reperfusion

Abstract

Oxygen Extraction Fraction (OEF) is a critical measure of a tissue's metabolic state post-ischemic stroke. This study investigated OEF changes in stroke-affected tissue compared to healthy tissue, post-reperfusion. OEF maps generated from gradient echo MRI images of 87 ischemic stroke patients at three time points after successful Endovascular Thrombectomy (EVT) were analysed in a prospective longitudinal multicentre study. Regions of interest (ROIs) delineating the infarct areas and corresponding mirror regions were drawn. The MR-derived OEF index values were obtained from the ROIs and compared using Wilcoxon signed rank tests. The cross-sectional comparison of OEF index values revealed lower values in the infarct areas than the corresponding contralateral areas at all three time points after successful EVT, presented as median (interquartile range) [24-72 hours: 20.84 (17.56-26.82)% vs 27.56 (23.22-31.87)%; 3 months: 27.37 (23.28-30.35)% vs 32.55 (28.00-35.81)%; 12 months: 24.38 (22.35-29.77)% vs 29.39 (25.86-34.04)%, p < 0.001 for all three time points]. Longitudinally, relative OEF index values increased gradually over time [24-72 hours: 0.81 (0.67-0.87); 3 months: 0.86 (0.79-0.95); 12 months: 0.88 (0.75-0.95)]. The findings revealed that following successful EVT, OEF in infarct tissue improves over time, indicating potential tissue recovery.Trial registration name and URL: Post-Reperfusion Pathophysiology in Acute Ischemic Stroke https://trialsearch.who.int/Trial2.aspx?TrialID=ACTRN12624000629538.

Keywords: Heterogeneity; infarct; ischemic stroke; oxygen extraction fraction; successful reperfusion; tissue changes; tissue recovery.

Figure 1.

Representative DWI images without (a) and with ROI shading (b), and OEF (c) images of a 37-year-old female with a left MCA occlusion, presenting with NIHSS of 18, and complete reperfusion (mTICI 3). The red and green ROIs represent the infarct and contralateral tissue, respectively.

Figure 2.

Distribution of OEF values within the different ROIs drawn on the OEF images of a 58-year-old male patient with a left MCA occlusion, presenting NIHSS 18, and an mTICI score 2 b.

Figure 3.

Patient selection flowchart.

Figure 4.

Cross-sectional and longitudinal analysis of OEF, mean standard deviation and mean skewness. Upper row (a-c): Cross – sectional comparison of mean OEF (a), mean skewness (b) and mean standard deviation values (c) of infarct and contralateral ROIs of all patients (n = 62). Number of patients at each timepoint after reperfusion: 53 patients at 24–72 hours, 40 patients at 3 months, and 33 patients at 12 months. Lower row (d-f): Longitudinal changes in relative mean OEF (d), infarct standard deviation (e) and infarct skewness in patients with complete imaging at all three time points (n = 23). * = less than 0.05, ** = less than 0.005, *** = less than 0.0005, **** = less than 0.00005, ns = not significant.