Gadonanotubes boost MRI contrast

Researchers at Rice University, the Baylor College of Medicine, the University of Houston and the Ecole Polytechnique Federale de Lausanne in Switzerland have created what they claim is a new class of magnetic resonance imaging contrast agents that are at least 40 times more effective than the best in clinical use.

The 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 nanotube of pure carbon.

Shrouding the toxic metals inside the benign carbon is expected to significantly reduce or eliminate the metal's toxicity.

Wilson and colleagues use short segments of nanotubes, tiny cylinders of pure carbon about one billionth of a metre, or one nanometre, 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.

Doctors use contrast agents in about 30% of MRIs. The contrast agents increase the sensitivity of the scans, making it easier for doctors to deliver a diagnosis. Gadolinium agents are the most effective agents and the most commonly used.

In the future, the researchers hope to use existing methods of attaching disease-specific antibodies and peptides to gadonanotubes so they can be targeted to cancerous tumours and other diseased cells.