Quantitative Mapping of Cerebral Metabolic Rate of Oxygen (CMRO2) Using Quantitative Susceptibility Mapping (QSM)

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Purpose:To quantitatively map cerebral metabolic rate of oxygen (Symbol) and oxygen extraction fraction (Symbol) in human brains using quantitative susceptibility mapping (QSM) and arterial spin labeling-measured cerebral blood flow (CBF) before and after caffeine vasoconstriction.Methods:Using the multiecho, three-dimensional gradient echo sequence and an oral bolus of 200 mg caffeine, whole brain Symbol and Symbol were mapped at 3-mm isotropic resolution on 13 healthy subjects. The QSM-based Symbol was compared with an Symbol-based Symbol to analyze the regional consistency within cortical gray matter (CGM) with the scaling in the Symbol method set to provide same total Symbol as the QSM method for each subject.Results:Compared to precaffeine, susceptibility increased (5.1 ± 1.1 ppb; P < 0.01) and Symbol decreased (−23.6 ± 6.7 ml/100 g/min; P < 0.01) at 25-min postcaffeine in CGM. This corresponded to a Symbol of 153.0 ± 26.4 μmol/100 g/min with an Symbol of 33.9 ± 9.6% and 54.5 ± 13.2% (P < 0.01) pre- and postcaffeine, respectively, at CGM, and a Symbol of 58.0 ± 26.6 μmol/100 g/min at white matter. Symbol from both QSM- and Symbol-based methods showed good regional consistency (P > 0.05), but quantitation of Symbol-based Symbol required an additional scaling factor.Conclusion:QSM can be used with perfusion measurements pre- and postcaffeine vascoconstriction to map Symbol and OEF. Magn Reson Med 74:945–952, 2015. © 2014 Wiley Periodicals, Inc.

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