It's hard to measure a tiny, fleeting gas called nitric oxide inside the body, but new high-tech tools are now letting scientists track where and when it shows up in the heart, brain, and tumors.

This study doesn’t test new gadgets, but it says measuring nitric oxide in the body is hard — and we really need better ways to do it, especially for diseases like heart problems and cancer. That matches the claim that new tools are helping us finally track it in real time.