Quantification of oxygen metabolic rates in Human brain with dynamic O MRI: Profile likelihood analysis.

Purpose: Parameter identifiability and confidence intervals were determined using a profile likelihood (PL) analysis method in a quantification model of the cerebral metabolic rate of oxygen consumption (CMRO ) with direct O MRI.

Methods: Three-dimensional dynamic O MRI datasets of the human brain were acquired after inhalation of O gas with the help of a rebreathing system, and CMRO was quantified with a pharmacokinetic model. To analyze the influence of the different model parameters on the identifiability of CMRO , PLs were calculated for different settings of the model parameters. In particular, the O enrichment fraction of the inhaled O gas, α, was investigated assuming a constant and a linearly varying model. Identifiability was analyzed for white and gray matter, and the dependency on different priors was studied.

Results: Prior knowledge about only one α-related parameter was sufficient to resolve the CMRO nonidentifiability, and CMRO rates (0.72-0.99 µmol/g /min in white matter, 1.02-1.78 µmol/g /min in gray matter) are in a good agreement with the results of O positron emission tomography studies. Nonconstant α values significantly improved model fitting.

Conclusion: The profile likelihood analysis shows that CMRO can be measured reliably in O gas MRI experiment if the O enrichment fraction is used as prior information for the model calculations. Magn Reson Med 78:1157-1167, 2017. © 2016 International Society for Magnetic Resonance in Medicine.