Cerebral oxygen extraction fraction: Comparison of dual‐gas challenge calibrated BOLD with CBF and challenge‐free gradient echo QSM+qBOLD

Purpose To compare cortical gray matter oxygen extraction fraction (OEF) estimated from 2 MRI methods: (1) the quantitative susceptibility mapping (QSM) plus quantitative blood oxygen level dependent imaging (qBOLD) (QSM+qBOLD or QQ), and (2) the dual‐gas calibrated‐BOLD (DGCB) in healthy subjects; and to investigate the validity of iso‐cerebral metabolic rate of oxygen consumption assumption during hypercapnia using QQ. Methods In 10 healthy subjects, 3 tesla MRI including a multi‐echo gradient echo sequence at baseline and hypercapnia for QQ, as well as an EPI dual‐echo pseudo‐continuous arterial spin labeling for DGCB, were performed under a hypercapnic and a hyperoxic condition. OEFs from QQ and DGCB were compared using region of interest analysis and paired t test. For QQ, cerebral metabolic rate of oxygen consumption = cerebral blood flow*OEF*arterial oxygen content was generated for both baseline and hypercapnia, which were compared. Results Average OEF in cortical gray matter across 10 subjects from QQ versus DGCB was 35.5 ± 6.7% versus 38.0 ± 9.1% ( P = .49) at baseline and 20.7 ± 4.4% versus 28.4 ± 7.6% ( P = .02) in hypercapnia: OEF in cortical gray matter was significantly reduced as measured in QQ ( P < .01) and in DGCB ( P < .01). Cerebral metabolic rate of oxygen consumption (in μmol O 2 /min/100 g) was 168.2 ± 54.1 at baseline from DGCB and was 153.1 ± 33.8 at baseline and 126.4 ± 34.2 ( P < .01) in hypercapnia from QQ. Conclusion The differences in OEF obtained from QQ and DGCB are small and nonsignificant at baseline but are statistically significant during hypercapnia. In addition, QQ shows a cerebral metabolic rate of oxygen consumption decrease (17.4%) during hypercapnia.