Tiny iron fillings injected into patients can work as monitoring devices for medical therapies, according to a study published this week in the journal Circulation: Cardiovascular Imaging, reports HealthDay News. First, researchers tag immune cells with microscopic iron fillings before injecting them into a patient's bloodstream. Then they track the fillings using magnetic resonance imaging. According to study co-author David Newby, a professor and chair of cardiology at the Centre for Cardiovascular Science at the University o f Edinburgh in Scotland, the process is completely safe and holds potential for tracking stem cell treatments. "We needed to be able to know if they wander off," Newby said, according to HealthDay. Article