The new agents -- dubbed gadonanotubes -- use the same highly toxic metal, gadolinium, that is given to more than a quarter of MRI patients today, but the metal atoms are encased inside a hollow tube of pure carbon called a nanotube. Shrouding the toxic metals inside the benign carbon is expected to significantly reduce or eliminate the metal's toxicity.
The research was published this month in the journal Chemical Communications.
"In prior work, we have boosted the effectiveness of gadolinium MRI contrast agents by encasing them in spheres of carbon called buckyballs," said lead author Lon Wilson, professor of chemistry at Rice. "Each nanotube will hold more gadolinium atoms than a buckyball, so we expected them to be more effective agents. But they are actually much, much better than we anticipated, so much so that no existing theory can explain how they work."
Wilson and colleagues use short segments of nanotubes, tiny cylinders of pure carbon about one billionth of a meter, or one nanometer, in diameter. That's about as wide as a strand of DNA. The ultrashort segments are only about 20-100 times longer than they are wide, and once inside the nanotubes, the gadolinium atoms naturally aggregate into tiny clusters of about 10 atoms each. Wilson and colleagues suspect the clustering is causing the unexplained increases in magnetic and MRI effects that they observed in tests at Rice, at the University of Houston's Texas Center for Superconductivity, and in the Swiss laboratories.
More than 25 million patients in the U.S. undergo MRIs each year. Doctors use contrast agents in about 30 percent of MRIs. The contrast agents increase t