Energy metabolism in human masseter muscle observed by mfMRI and 31P-MRS

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1. T2 mapping of the individual masseter muscles showed that 30% MVC produces significant increases in the values. The T2 relaxation time decreased rapidly after the contraction. 2. Using 31P-MRS, it was observed that muscle activation produced significant decreases in the signal intensity of phosphocreatine (PCr), leading to recovery after releasing the 30% MVC, while the inorganic phosphate level (Pi) showed moderate increases and returned to its former condition.The current state of investigation indicates that the mechanism responsible for the increased T2 results from osmotically-driven shifts in the muscle water that increase the volume of the intracellular space, and from intracellular acidification. Both mfMRI and MRS, a quantitative noninvasive biochemical sampling technique, represent viable alternatives for metabolic studies of the masseter muscle.These findings suggested the effectiveness of both mfMRI and 31P-MRS as promising tools to study masseter muscle fatigue.