Feasibility of mapping unidirectional Pi-to-ATP fluxes in muscles of the lower leg at 7.0 Tesla.

PURPOSE: To assess the feasibility of mapping the kinetics and unidirectional fluxes of inorganic phosphate (Pi) to adenosine triphosphate (ATP) reactions in the entire volume of the lower leg muscles using a three-dimensional saturation transfer (ST) phosphorus (31 P) imaging sequence. THEORY AND METHODS: We imaged the lower leg muscles of five healthy subjects at 7.0 Tesla. The total experimental time was 45 min. We quantified muscle-specific forward reaction rate constants (k'f ) and metabolic fluxes (Vf ) of the Pi-to-ATP reaction in the tibialis anterior, the gastrocnemius, and the soleus. RESULTS: In the tibialis anterior, k'f and Vf were 0.11 s-1 ± 0.03 (mean ± standard deviation) and 0.34 mM s-1 ± 0.10, respectively. In the gastrocnemius, k'f was 0.11 s-1 ± 0.04 and Vf was 0.37 mM s-1 ± 0.11, while in the soleus muscle k'f was 0.10 s-1 ± 0.02 and Vf was 0.36 mM s-1 ± 0.14. CONCLUSION: Our results suggest that mapping the kinetics and unidirectional fluxes from Pi-to-ATP in both the anterior and posterior muscles of the lower leg is feasible at ultra-high field and may provide useful insights for the study of insulin resistance, diabetes and aging. Magn Reson Med 74:225-230, 2015. © 2014 Wiley Periodicals, Inc.