PET Scan (IMAGE) University of Missouri-Columbia Caption By tagging auxin with a radioactive tracer, the researchers were able to use a medical diagnostic imaging tool call positron emission tomography, or PET imaging, to "watch" the movement of auxin in living plant roots in real time. Credit Richard Ferrieri Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.