Phase-based regional oxygen metabolism in magnetic resonance imaging at high field

Abstract

Venous oxygen saturation (Yv) in cerebral veins and the cerebral metabolic rate of oxygen (CMRO₂) are important indicators for brain function and disease. Phase-susceptibility measurements in magnetic resonance imaging (MRI) have been used to quantify Yv in candidate cerebral veins. However, currently there is no method to quantify regional CMRO₂ using MRI. Here we propose a novel technique to quantify CMRO₂ from independent MRI estimates of Yv and cerebral blood flow (CBF). Our approach used standard gradient-echo (GRE) and arterial spin labeling (ASL) to make these measurements. Results for in vivo Y, and CMRO₂ estimates on human subjects are presented from application of our technique at 3 Tesla (3T). We also extended our method to high-field human imaging at 7 Tesla (7T), which allows us to take advantage of improved signal-to-noise ratio (SNR) for the same scan duration to achieve higherresolution analysis of vessels of interest. While the higher field strength poses additional challenges, such as increased main field and excitation field inhomogeneities as well as more severe susceptibility artifacts, initial results suggest that substantial benefits can be realized with phase-based regional oxygen metabolism in MRI at high field.