Nanotubes a Source of MRI Contrast Agents

The new agents, called gadonanotubes, use the same very toxic metal, gadolinium, that is administered to more than one-fourth of MRI patients currently scanned with MRI, but the metal atoms are enclosed inside a hollow nanotube of pure carbon. Blanketing the toxic metals inside the harmless carbon is expected to considerably reduce or eliminate the metal's toxicity to patients.

The gadonanotubes were created by scientists from the Rice University (Houston, TX, USA), Baylor College of Medicine (Houston, TX, USA), and the University of Houston (TX, USA), and the Ecole Polytechnique Fédérale de Lausanne (Switzerland). They have succeeded in creating a new class of MRI contrast agents that are at least 40 times more effective than the best in current clinical use.

The study was published in the August 2005 issue of 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 Dr. Lon Wilson, professor of chemistry at Rice and lead author of the study. "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.”

Dr. Wilson and coworkers used short segments of nanotubes, tiny tubes of pure carbon about one billionth of a meter, or 1 nm, in diameter, which is approximately as wide as a strand of DNA. The very short segments are only about 20-100 times longer than they are wide, and once inside the nanotubes, the gadolinium atoms naturally amass into tiny clusters of about 10 atoms each. The researchers suspect the clustering is causing the unexplained increases in magnetic and MRI effects that they noted in tests at Rice, at the University of Houston's Texas Center for Superconductivity, and in the Swiss laboratories.

These contrast agents increase the sensitivity of the scans, making it easier to obtain a diagnosis. Gadolinium agents are the most effective agents and the most typically used. The investigators hope in the near future to use existing methods of attaching disease-specific antibodies and peptides to gadonanotubes so they can be targeted to cancerous tumors and other diseased cells.





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