QQ ‐Based Oxygen Extraction Fraction ( OEF ) Mapping in Mouse Brain: Initial Experience

Purpose Oxygen extraction fraction (OEF) is a vital biomarker of cerebral oxygen metabolism and tissue viability. A novel OEF mapping method, QQ, which combines quantitative susceptibility mapping (QSM) and quantitative blood oxygen level‐dependent (qBOLD) (QSM + qBOLD = QQ), has demonstrated promise in detecting disease‐related OEF abnormalities in humans. However, its application in preclinical mouse models remains untested. This study evaluates the feasibility and short‐term within‐session repeatability of the QQ method to capture physiological changes in the mouse brain. Methods In vivo MRI was performed on five C57BL/6 mice under four isoflurane anesthesia levels (1%, 1.5%, 2% and 2.5%). OEF maps were reconstructed using the QQ‐CCTV algorithm. The relationship between anesthesia depth and OEF was analyzed using linear mixed‐effects models. Repeatability was quantified via Bland–Altman plots and the within‐subject coefficient of variation (CV). Results The QQ method generated relatively uniform OEF maps, capturing a significant, dose‐dependent decrease in OEF with increasing isoflurane concentrations across the whole brain and targeted ROIs. Within‐session repeatability of the QQ method was assessed at each isoflurane level using repeated‐measures Bland–Altman analysis and the within‐subject CV (9.7%–13.8%). Conclusion This first application of the QQ method in the mouse brain demonstrates its feasibility for spatially resolved OEF quantification and lays the groundwork for future studies investigating oxygen metabolism in animal models.