Quantitative susceptibility mapping-based cerebral metabolic rate of oxygen mapping with minimum local variance

Purpose: The objective of this study was to demonstrate the feasibility of a cerebral metabolic rate of oxygen (CMRO₂) mapping method based on its minimum local variance (MLV) without vascular challenge using quantitative susceptibility mapping (QSM) and cerebral blood flow (CBF). Methods: Three-dimensional multi-echo gradient echo imaging and arterial spin labeling were performed in 11 healthy subjects to calculate QSM and CBF. Minimum local variance was used to compute whole-brain CMRO₂ map from QSM and CBF. The MLV method was compared with a reference method using the caffeine challenge. Their agreement within the cortical gray matter (CGM) was assessed on CMRO₂ and oxygen extraction fraction (OEF) maps at both baseline and challenge states. Results: Mean CMRO₂ (in µmol/100 g/min) obtained in CGM using the caffeine challenge and MLV were 142 ± 16.5 and 139 ± 14.8 µmol/100 g/min, respectively; the corresponding baseline OEF were 33.0 ± 4.0% and 31.8 ± 3.2%, respectively. The MLV and caffeine challenge methods showed no statistically significant differences across subjects with small (< 4%) biases in CMRO₂ and OEF values. Conclusions: Minimum local variance–based CMRO₂ mapping without vascular challenge using QSM and arterial spin labeling is feasible in healthy subjects. Magn Reson Med 79:172–179, 2018.