Time-resolved phosphorous magnetization transfer of the human calf muscle at 3T and 7T: A feasibility study

Abstract: Phosphorous (31P) magnetization transfer (MT) experiments enable the non-invasive investigation of human muscle metabolism in various physiological and pathological conditions. The purpose of our study was to investigate the feasibility of time-resolved MT, and to compare the results of MT experiments at 3T and 7T. Six healthy volunteers were examined on a 3T and a 7T MR scanner using the same setup and identical measurement protocols. In the calf muscle of all volunteers, four separate MT experiments (each ∼10min duration) were performed in one session. The forward rate constant of the ATP synthesis reaction (k ATP) and creatine kinase reaction (k CK), as well as corresponding metabolic fluxes (F ATP, F CK), were estimated. A comparison of these exchange parameters, apparent T 1s, data quality, quantification precision, and reproducibility was performed. The data quality and reproducibility of the same MT experiments at 7T was significantly higher (i.e., k ATP 2.7 times higher and k CK 3.4 times higher) than at 3T (p <0.05). The values for k ATP (p =0.35) and k CK (p =0.09) at both field strengths were indistinguishable. Even a single MT experiment at 7T provided better data quality than did a 4 times-longer MT experiment at 3T. The minimal time-resolution to reliably quantify both F ATP and F CK at 7T was ∼6min. Our results show that MT experiments at 7T can be at least 4 times faster than 3T MT experiments and still provide significantly better quantification. This enables time-resolved MT experiments for the observation of slow metabolic changes in the human calf muscle at 7T. [Copyright &y& Elsevier]