title: Comparison of hypercapnia-based calibration techniques for measurement of cerebral oxygen metabolism with MRI.
abstract: MRI may be used to measure fractional changes in cerebral oxygen metabolism via a metabolic model. One step commonly used in this measurement is calibration with image data acquired during hypercapnia, which is a state of increased CO2 content of the blood. In this study some commonly used hypercapnia-inducing stimuli were compared to assess their suitability for the calibration step. The following stimuli were investigated: (a) inspiration of a mixture of 4% CO2, 21% O2 and balance N2; (b) 30-s breath holding; and (c) inspiration of a mixture of 4% CO2 and 96% O2 (i.e., carbogen). Measurements of BOLD and cerebral blood flow made on nine subjects during the different hypercapnia-inducing stimuli showed that each stimulus leads to a different calibration of the model. We argue that of the aforementioned stimuli, inspiration of 4% CO2, 21% O2 and balance N2 should be preferred for the calibration as the other stimuli produce responses that violate assumptions of the metabolic model.
authors.affiliation: FMRIB Centre, Department of Clinical Neurology, University of Oxford, United Kingdom. bulte@fmrib.ox.ac.uk
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Bulte
authors.forename: Knut
authors.initials: K
authors.lastname: Drescher
authors.forename: Peter
authors.initials: P
authors.lastname: Jezzard
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000378:metabolism*; D002138:Calibration; D006801:Humans; D006935:Hypercapnia / Q000378:metabolism*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000592:standards; D008297:Male; D010092:Oximetry / Q000379:methods* / Q000592:standards; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D010100:Oxygen