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

Area of Science:

• Neuroimaging
• Biophysics
• Medical Physics

Background:

• Accurate quantification of regional brain oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen consumption (CMRO2) is crucial for understanding brain physiology and disease.
• Quantitative susceptibility mapping (QSM) and dual-gas calibrated BOLD imaging (DGC-BOLD) are advanced MRI techniques used for these measurements.
• Comparing these methods is essential to determine their relative strengths and weaknesses.

Purpose of the Study:

• To compare regional OEF and CMRO2 quantified by microvascular QSM with a hypercapnic challenge against those measured by DGC-BOLD in healthy subjects.
• To evaluate the feasibility and intersubject variability of the QSM-based approach for OEF and CMRO2 quantification.

Main Methods:

• Ten healthy subjects underwent 3T MRI scanning.
• QSM data were acquired at baseline and during hypercapnia using a multi-echo gradient-echo sequence.
• Cerebral blood flow was measured using pseudo-continuous arterial spin labeling.
• DGC-BOLD data were collected under hypercapnic and hyperoxic conditions.
• Regional OEF and CMRO2 were calculated and compared between QSM and DGC-BOLD using region of interest analysis and Bland-Altman plots.

Main Results:

• Hypercapnia served as a robust stimulus for QSM-based OEF mapping.
• Average OEF was 0.40 ± 0.04 by QSM-OEF and 0.38 ± 0.09 by DGC-BOLD.
• Average CMRO2 was 176 ± 35 μmol O2/min/100g by QSM-OEF and 167 ± 53 μmol O2/min/100g by DGC-BOLD.
• Bland-Altman analysis revealed statistically significant but small differences between the two methods for regional OEF and CMRO2.

Conclusions:

• Hypercapnic challenge-assisted QSM-OEF is a feasible method for quantifying regional brain OEF and CMRO2.
• Compared to DGC-BOLD, hypercapnia QSM-OEF demonstrates smaller intersubject variability.
• The QSM method requires only a single gas challenge, potentially simplifying the imaging protocol.