Abstract
PurposeThis study aimed to assess the spatiotemporal evolution of oxygen extraction fraction (OEF) in ischemic stroke with a newly developed cluster analysis of time evolution (CAT) for a combined quantitative susceptibility mapping and quantitative blood oxygen level-dependent model (QSM + qBOLD, QQ).MethodOne hundred and fifteen patients in different ischemic stroke phases were retrospectively collected for measurement of OEF of the infarcted area defined on diffusion-weighted imaging (DWI). Clinical severity was assessed using the National Institutes of Health Stroke Scale (NIHSS). Of the 115 patients, 11 underwent two longitudinal MRI scans, namely, three-dimensional (3D) multi-echo gradient recalled echo (mGRE) and 3D pseudo-continuous arterial spin labeling (pCASL), to evaluate the reversal region (RR) of the initial diffusion lesion (IDL) that did not overlap with the final infarct (FI). The temporal evolution of OEF and the cerebral blood flow (CBF) in the IDL, the RR, and the FI were assessed.ResultsCompared to the contralateral mirror area, the OEF of the infarcted region was decreased regardless of stroke phases (p < 0.05) and showed a declining tendency from the acute to the chronic phase (p = 0.022). Five of the 11 patients with longitudinal scans showed reversal of the IDL. Relative oxygen extraction fraction (rOEF, compared to the contralateral mirror area) of the RR increased from the first to the second MRI (p = 0.044). CBF was about 1.5-fold higher in the IDL than in the contralateral mirror area in the first MRI. Two patients showed penumbra according to the enlarged FI volume. The rOEF of the penumbra fluctuated around 1.0 at earlier scan times and then decreased, while the CBF decreased continuously.ConclusionThe spatiotemporal evolution of OEF and perfusion in ischemic lesions is heterogeneous, and the CAT-based QQ method is feasible to capture cerebral oxygen metabolic information.
Highlights
Ischemic stroke is one of the leading causes of disability and mortality globally (Kim et al, 2020)
The oxygen extraction fraction (OEF) of the infarcted area identified on DWI was significantly lower than that of the contralateral mirror area regardless of stroke phases
We explored the spatiotemporal evolution of OEF in ischemic stroke by means of cluster analysis of time evolution (CAT)-based QSM + qBOLD (QQ)
Summary
Ischemic stroke is one of the leading causes of disability and mortality globally (Kim et al, 2020). The oxygen extraction fraction (OEF) is the relative difference of the oxygen concentration between arterial and venous blood, a practical parameter representing the oxygen consumption of brain tissue. It plays a vital role in sustaining the normal coupling between cerebral blood flow (CBF) and the cerebral metabolic rate of oxygen (CMRO2), as expressed by the following equation: CMRO2 = OEF · CBF · [H]a where [H]a is the oxygenated heme molar concentration in the arteriole (Zhang et al, 2018). Advancement in imaging technology is of great benefit to the diagnosis and therapeutic strategy making for ischemic stroke; the oxygenation status of an ischemic brain tissue has a broad range depending on the blood supply and the time from stroke onset, and there are few studies systematically reporting the oxygenation status through different time points and blood flow
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