Quantitative and simultaneous measurement of oxygen consumption rates in rat brain and skeletal muscle using 17 O MRS imaging at 16.4T

Abstract

Purpose: Oxygen-17 (¹⁷ O) MRS imaging, successfully used in the brain, is extended by imaging the oxygen metabolic rate in the resting skeletal muscle and used to determine the total whole-body oxygen metabolic rate in the rat.

Methods: During and after inhalations of ¹⁷ O₂ gas, dynamic ¹⁷ O MRSI was performed in rats (n = 8) ventilated with N₂ O or N₂ at 16.4 T. Time courses of the H₂¹⁷ O concentration from regions of interest located in brain and muscle tissue were examined and used to fit an animal-adapted 3-phase metabolic model of oxygen consumption. CBF was determined with an independent washout method. Finally, body oxygen metabolic rate was calculated using a global steady-state approach.

Results: Cerebral metabolic rate of oxygen consumption was 1.97 ± 0.19 μmol/g/min on average. The resting metabolic rate of oxygen consumption in skeletal muscle was 0.32 ± 0.12 μmol/g/min and >6 times lower than cerebral metabolic rate of oxygen consumption. Global oxygen consumed by the body was 24.2 ± 3.6 mL O₂ /kg body weight/min. CBF was estimated to be 0.28 ± 0.02 mL/g/min and 0.34 ± 0.06 mL/g/min for the N₂ and N₂ O ventilation condition, respectively.

Conclusion: We have evaluated the feasibility of ¹⁷ O MRSI for imaging and quantifying the oxygen consumption rate in low metabolizing organs such as the skeletal muscle at rest. Additionally, we have shown that CBF is slightly increased in the case of ventilation with N₂ O. We expect this study to be beneficial to the application of ¹⁷ O MRSI to a wider range of organs, although further validation is advised.

Keywords: 17O MRSI of H217O; cerebral blood flow (CBF); cerebral metabolic rate of oxygen (CMRO2); mitochondrial water; muscle resting metabolic rate of oxygen consumption; skeletal muscle metabolism; total body oxygen consumption (VO2).