Test-retest reproducibility of a rapid method to measure brain oxygen metabolism

Cerebral metabolic rate of oxygen (CMRO₂) is an important index of tissue viability and brain function, but this parameter cannot yet be measured routinely on clinical scanners. Recently, a noninvasive technique was proposed which estimates global CMRO₂ by concomitantly measuring oxygen-extraction-fraction using T₂-relaxation-under-spin-tagging MRI and pulse oximetry, and cerebral-blood-flow using phase-contrast MRI. This study sought to establish a standard acquisition procedure for this technique and to evaluate its test-retest reproducibility in healthy subjects. Each subject was examined in five sessions and each session included two measurements. Intrasession, intersession, and intersubject coefficients of variation for CMRO₂ were found to be 3.84 ± 1.44% (N = 7, mean ± standard deviation), 6.59 ± 1.56%, and 8.80% respectively. These reproducibility values were comparable or slightly superior to ¹⁵O positron emission tomography (PET) results reported in the literature. It was also found that oxygen-extraction-fraction and cerebral-blood-flow tended to co-vary across sessions (P = 0.002) and subjects (P = 0.01), and their coefficients of variation were greater than that of CMRO₂. The simplicity and reliability features may afford this global CMRO₂ technique great potential for immediate clinical applications.