Artwork of MRI Contrast Agents (image) California Institute of Technology Share Print E-Mail Caption Caltech's Mikhail Shapiro and his colleagues have developed "erasable" MRI contrast agents that can blink off on command with ultrasound technology. As illustrated here, the contrast agents -- which consist of air-filled protein structures called gas vesicles -- give off magnetic signals. When hit with waves of sound, the gas vesicles collapse and their signals go away. This makes it easier for researchers to interpret MRI scans. Credit Barth van Rossum for Caltech Usage Restrictions Please use credit. Share Print E-Mail 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.