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Researchers are working on “erasable” contrast agents that would have the ability to blink off, on command, thereby revealing their location in the body.

The new technology relies on nanoscale structures called gas vesicles, which are naturally produced by some microbes. Gas vesicles consist of a protein shell with a hollow interior and are used by the microbes as flotation devices to regulate access to light and nutrients.

The gas vesicles stand out in MRI scans because the air in their chambers reacts differently to magnetic fields compared to the aqueous tissues around them. This results in a local darkening of MRI images where the gas vesicles are present.

MRI contrast agents that can blink off on command with ultrasound technology. (Credit: Barth van Rossum for Caltech)

In the new study, performed in mice, the researchers showed that gas vesicles could indeed be used as MRI contrast agents — the gas vesicles were detected in certain tissues and organs, such as the brain and liver. What's more, the gas vesicles could be turned off. When hit with ultrasound waves of a high enough pressure, the cylindrical structures “collapsed like crushed soda cans,” Shapiro says, and their magnetic signals went away.

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