Phase‐based regional oxygen metabolism (PROM) using MRI

Abstract

Venous oxygen saturation (Y_v) in cerebral veins and the cerebral metabolic rate of oxygen (CMRO₂) are important indicators for brain function and disease. Although MRI has been used for global measurements of these parameters, currently there is no recognized technique to quantify regional Y_v and CMRO₂ using noninvasive imaging. This article proposes a technique to quantify CMRO₂ from independent MRI estimates of Y_v and cerebral blood flow. The approach uses standard gradient‐echo and arterial spin labeling acquisitions to make these measurements. Using MR susceptometry on gradient‐echo phase images, Y_v was quantified for candidate vein segments in gray matter that approximate a long cylinder parallel to the main magnetic field. Local cerebral blood flow for the identified vessel was determined from a corresponding region in the arterial spin labeling perfusion map. Fick's principle of arteriovenous difference was then used to quantify CMRO₂ locally around each vessel. Application of this method in young, healthy subjects provided gray matter averages of 59.6% ± 2.3% for Y_v, 51.7 ± 6.4 mL/100 g/min for cerebral blood flow, and 158 ± 18 μmol/100 g/min for CMRO₂ (mean ± SD, n = 12), which is consistent with values previously reported by positron emission tomography and MRI. Magn Reson Med, 2012.