NMR spectroscopy using C13-labeled glucose can track glucose metabolism and measure intracellular pathway flux non-invasively in humans.

“so that's carbon nmr so in our bodies 99 of the carbon in our body is c12 which is nmr invisible but one percent is c13 which is nmr visible has this precession properties you can use a labeled for example c1 labeled glucose and then track that c1 glucose as it gets into the say a muscle cell or liver cell and gets metabolized and finds its way into glycogen and then you can measure flux you can actually for the first time in humans non-invasively without any ionizing radiation measure how much is going in through measure intracellular pathway flux”