Nanotech News

August 29, 2005

Gadolinium-Loaded Ultra-Short Carbon Nanotubes Make Powerful MRI Contrast Agents

An international team of investigators has created a new class of magnetic resonance imaging (MRI) contrast agents that are at least 40 times more effective than the best in clinical use. 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 ultra-short carbon nanotubes.

Writing in the journal Chemical Communications, a team of investigators led by Lon Wilson, Ph.D., of Rice University, noted that ultra-short carbon nanotubes, made by fragmenting commercially available carbon nanotubes, are likely to be the most useful for in vivo applications because cells can take up this 20-100 nanometer long tubes more easily and the body can eventually eliminate them more readily than their longer progenitors. In addition, the fragmented nanotubes appear to take up more gadolinium than expected, producing a superior MRI contrast agent.

"In prior work, we have boosted the effectiveness of gadolinium MRI contrast agents by encasing them in spheres of carbon called buckyballs," said Dr. Wilson. “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.”

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 research laboratories based in Switzerland. 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 tumors and other diseased cells.

More than 25 million patients in the U.S. undergo MRI exams each year. Doctors use contrast agents in about 30 percent 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 MRI contrast agents and the most commonly used. (Click here to see two earlier stories on other nanotechnology-based approaches to creating gadolinium MRI contrast agents.)

This work is detailed in a paper titled, “Superparamagnetic gadonanotubes are high-performance MRI contrast agents.” Researchers from Baylor College of Medicine and the Ecole Polytechnique Fédérale de Lausanne, Switzerland, also participated in this study. An abstract is available through PubMed.
View abstract.