Phosphorus-31 NMR can measure high-energy phosphates like ATP, phosphocreatine, and inorganic phosphate in vivo without isotopes.

“there you don't have to give any isotopes there you actually see p31 phosphorus 31 is 100 natural abundant you see all the phosphorus that's in solution in our bodies so for example when our volunteers go into slide a magnet and we put a leg or arm into the magnet we can see all the high energy phosphates in for example atp adenosine triphosphate there are three phosphates and you can actually see each one of those phosphates you can see phosphocreatine has a different chemical shift you can see inorganic phosphate”