Nanotechnology gives unexplainable boost to MRI scan contrast agents
17 August 2005
Carbon nanotubes have have become an unexpected source of highly
effective contrast agents for enhancing MRI scans. 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 nanotube of pure carbon. Shrouding the toxic metals
inside the benign carbon is expected to significantly reduce or eliminate
the metal's toxicity to patients.
The gadonanotubes were created by researchers at Rice University,
the Baylor College of Medicine and the University of Houston, all in the
USA, and the Ecole Polytechnique Fédérale de Lausanne in Switzerland. They
have succeeded in creating a new class of magnetic resonance imaging (MRI)
contrast agents that are at least 40 times more effective than the best in
current clinical use.
The research was published this month in the journal Chemical
"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% 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
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.
Co-authors include Rice's Balaji Sitharaman, Kyle Kissell, Keith Hartman
and Lesa Tran; the University of Houston's Andrei Baikalov, Irene Rusakova
and Yanyi Sun; the Baylor College of Medicine's Htet Khant, Steven Ludtke
and Wah Chiu; and the Ecole Polytechnique Fédérale's Sabrina Laus, Eva Tóth,
Lothar Helm and André Merbach.
The research was funded by the U.S. National Institutes of Health, the
Welch Foundation, and the Swiss National Science Foundation and the Office
for Education and Science.
Links for more information
Baylor College of Medicine, Houston, Texas
University of Houston
Ecole Polytechnique Fédérale de Lausanne
MRI contrast agents explained: