Comparison of Hypercapnia-Based Calibration Techniques for Measurement of Cerebral Oxygen Metabolism With MRI

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-including 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% O-2 and balance N-2; (b) 30-s breath holding; and (c) inspiration of a mixture of 4% CO2 and 96% O-2 (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% O-2 and balance N-2 should be preferred for the calibration as the other stimuli produce responses that violate assumptions of the metabolic model. Magn Reson Med 61:391-398,2009. (c) 2009 Wiley-Liss, Inc.