Unique advantages of dynamic L-[¹¹C] methionine PET/CT for assessing the rate of skeletal muscle protein synthesis: A pilot trial in young men

Although the standard method to evaluate skeletal muscle protein synthesis (MPS) is muscle biopsy, the method is invasive and problematic for multisite use. We conducted a small pilot study in volunteers to investigate changes in MPS according to skeletal muscle site using a noninvasive method in which 6 healthy young men were given yogurt (containing 20 g milk protein) or water, and 1 h later, L-[¹¹C]methionine ([¹¹C]Met) was administered intravenously. Dynamic PET/CT imaging of their thighs was performed for 60 min. The influx constant K_i of [¹¹C]Met in skeletal muscle protein was calculated as an index of MPS using a Patlak plot, and found to be 0.6%–28% higher after ingesting yogurt than after water in 5 of the 6 volunteer participants, but it was 34% lower in the remaining participant. Overall, this indicated no significant increase in K_i after ingesting milk protein. However, when the quadriceps and hamstring muscles were analyzed separately, we found a significant difference in K_i. This demonstrates the potential of visualizing MPS by calculating the K_i for each voxel and reconstructing it as an image, which presents unique advantages of [¹¹C]Met PET/CT for evaluating MPS, such as site-specificity and visualization.