Could we use the energy from light and sound to detect disease? TED Fellow Lei Li shares the exciting promise of photoacoustic imaging: an affordable, painless and accurate method of converting light into sound in order to create high-resolution images of what's going on inside our bodies. From early detection of breast cancer to steering medicine-delivering micro-robots, learn how this cutting-edge technology could open up a new world of possibility when it comes to seeing, tracking and diagnosing disease.