Cerebral OEF quantification: A comparison study between quantitative susceptibility mapping and dual-gas calibrated BOLD imaging

Abstract

Purpose: To compare regional oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen consumption (CMRO₂ ) quantified from the microvascular quantitative susceptibility mapping (QSM) using a hypercapnic gas challenge with those measured by the dual-gas calibrated BOLD imaging (DGC-BOLD) in healthy subjects.

Methods: Ten healthy subjects were scanned using a 3T MR system. The QSM data were acquired with a multi-echo gradient-echo sequence at baseline and hypercapnia. Cerebral blood flow data were acquired using the pseudo-continuous arterial spin labeling technique. Baseline OEF and CMRO₂ were calculated using QSM and cerebral blood flow measurements. The DGC-BOLD data were also collected under a hypercapnic and a hyperoxic condition to yield baseline OEF and CMRO₂ . The QSM-OEF and CMRO₂ maps were compared with DGC-BOLD OEF and CMRO₂ maps using region of interest (vascular territories) analysis and Bland-Altman plots.

Results: Hypercapnia is a robust stimulus for mapping OEF in combination with QSM. Average OEF in 16 vascular territory regions of interest across 10 subjects was 0.40 ± 0.04 by QSM-OEF and 0.38 ± 0.09 by DGC-BOLD. The average CMRO₂ was 176 ± 35 and 167 ± 53 μmol O₂ /min/100g by QSM-OEF and DGC-BOLD, respectively. A Bland-Altman plot of regional OEF and CMRO₂ in regions of interest revealed a statistically significant but small difference (OEF difference = 0.02, CMRO₂ difference = 9 μmol O₂ /min/100g, p < .05) between the 2 methods for the 10 healthy subjects.

Conclusion: Hypercapnic challenge-assisted QSM-OEF is a feasible approach to quantify regional brain OEF and CMRO₂ . Compared with DGC-BOLD, hypercapnia QSM-OEF results in smaller intersubject variability and requires only 1 gas challenge.

Keywords: calibrated BOLD; oxygen extraction fraction; quantitative susceptibility mapping.