The question that inspired the technique was: how do we spot leaks from the gut after gastric surgery?

Neither ultrasound, CT or MRI scanning could be used to remotely determine local chemistry around the internal wound, according to Northwestern University, which teamed up with the Washington University School of Medicine in St. Louis to find an answer: fingerprint-sized stickers that can be left inside the patient on which a ring of circular metallic discs are deposited.