Quantitative mapping of cerebral metabolic rate of oxygen (CMRO2 ) using quantitative susceptibility mapping (QSM).

PURPOSE: To quantitatively map cerebral metabolic rate of oxygen ( CMRO2) and oxygen extraction fraction ( OEF) 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 CMRO2 and OEF were mapped at 3-mm isotropic resolution on 13 healthy subjects. The QSM-based CMRO2 was compared with an R2*-based CMRO2 to analyze the regional consistency within cortical gray matter (CGM) with the scaling in the R2* method set to provide same total CMRO2 as the QSM method for each subject.

RESULTS: Compared to precaffeine, susceptibility increased (5.1 ± 1.1 ppb; P < 0.01) and CBF decreased (-23.6 ± 6.7 ml/100 g/min; P < 0.01) at 25-min postcaffeine in CGM. This corresponded to a CMRO2 of 153.0 ± 26.4 μmol/100 g/min with an OEF of 33.9 ± 9.6% and 54.5 ± 13.2% (P < 0.01) pre- and postcaffeine, respectively, at CGM, and a CMRO2 of 58.0 ± 26.6 μmol/100 g/min at white matter. CMRO2 from both QSM- and R2*-based methods showed good regional consistency (P > 0.05), but quantitation of R2*-based CMRO2 required an additional scaling factor.

CONCLUSION: QSM can be used with perfusion measurements pre- and postcaffeine vascoconstriction to map CMRO2 and OEF.