Quantification of brain oxygen extraction fraction using QSM and a hyperoxic challenge.

PURPOSE: To use hyperoxia in combination with QSM to quantify microvascular oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO ) in healthy subjects and to cross-validate results with those from hypercapnia QSM-OEF.

METHODS: Ten healthy subjects were scanned on a 3T MRI scanner. At baseline normoxia and during hyperoxia (PetO = +300 mmHg), QSM data were acquired using a multi-echo gradient-echo (GRE) sequence, and cerebral blood flow data were acquired using a pseudocontinuous arterial spin labeling sequence. The OEF and CMRO maps were computed and compared with those from hypercapnia QSM-OEF, acquired in the same subjects, using correlation and Bland-Altman analysis in 16 vascular territories.

RESULTS: Hyperoxia QSM-OEF produced physiologically reasonable OEF and CMRO values in all subjects (gray-matter region of interest average OEF = 0.42 ± 0.04, average CMRO = 181 ± 34 μmol O /min/100 g). When compared with hypercapnia QSM-OEF, Bland-Altman plots revealed small deviations (mean OEF difference = 0.015, mean CMRO difference = 4.9 μmol O /min/100 g, P < .05). Good and excellent correlations of regional OEF and CMRO were found for the two methods. In addition, hyperoxia had minimal impact on cerebral blood flow (average gray-matter cerebral blood flow was reduced by 7.5 ± 5.4%).

CONCLUSIONS: Hyperoxia in combination with QSM is a robust approach to measure OEF. Compared with hypercapnia, hyperoxia is more comfortable and has minimal impact on cerebral blood flow.