Dynamic measurement of oxygen extraction fraction using a multiecho asymmetric spin echo (MASE) pulse sequence.

Abstract

PurposeThe oxygen extraction fraction (OEF), an important parameter for assessing brain oxygen metabolism, is a key marker of brain health. Dynamic measurement of the OEF is currently limited by the long acquisition time. In this study, a noninvasive method for rapidly and effectively assessing dynamic changes in the OEF during brain stimulation is proposed.MethodsA novel pulse sequence using the multi‐echo asymmetric spin echo with an echo‐planar imaging acquisition scheme was developed to improve the temporal resolution of functional OEF measurements. A theoretical formulation that describes the multi‐echo asymmetric spin echo signal dephasing phenomena in the presence of deoxygenated hemoglobin was established. A functional motor experiment was performed using human subjects, in which both OEF maps using the multi‐echo asymmetric spin echo sequence and blood oxygenation level–dependent maps using a ‐weighted gradient‐echo echo‐planar imaging sequence were generated and compared.ResultsThe activation maps for both OEF and blood oxygenation level–dependent maps revealed significant changes in the motor cortex. Our results, which were consistent with the previous reports, showed that the average relative changes in the OEF and blood oxygenation level–dependent signal were −22% and 2.0%, respectively.ConclusionObtaining dynamic OEF measurements during functional experiments with the proposed multi‐echo asymmetric spin echo method is feasible. Magn Reson Med 80:1118–1124, 2018. © 2018 International Society for Magnetic Resonance in Medicine.