University of Texas at Dallas researchers are breathing new life into an old MR contrast agent by attaching it to a plant virus and wrapping it in a protective chemical cage.

The novel strategy is aimed at developing a completely organic and biodegradable compound that would eliminate the need to use heavy metals such as gadolinium in contrast agents, said Dr. Jeremiah Gassensmith, associate professor of chemistry and biochemistry in the School of Natural Sciences and Mathematics and corresponding author of a study published online Feb. 5 in the journal Chemical Science, a publication of the Royal Society of Chemistry.

MRI is a commonly used medical imaging technology that allows physicians to see soft tissues in the body. Some tissues, like cancer, are better seen when a patient is given a contrast agent, which makes diseased parts of the body show up brightly in an MRI scan. The only class of contrast agents approved for use with MRI in the U.S. is based on the heavy metal gadolinium, which is typically excreted through a patient's urine after an MRI is completed.
Because of its widespread use, gadolinium -- which is able to sneak through wastewater treatment plants -- is increasingly showing up in watersheds in and around large metropolitan areas.

"Gadolinium-based contrast agents are used so much and so often that, just from patients excreting it in their urine, the metal is being released into water resources and sediments," Gassensmith said. "The observed concentrations are still very low, but, nonetheless, it's not exactly clear what effects long-term accumulation of gadolinium might have on the body."

In addition, for patients with compromised kidneys who have difficulty excreting these contrast agents, gadolinium can increase the risk of further kidney damage.

"For these reasons, we wanted to come up with something that was biocompatible and biodegradable, something completely organic with no heavy metals," Gassensmith said. Gassensmith and his colleagues revisited a type of organic radical contrast agent, or ORCA, that had been previously considered as an MRI contrast agent but was abandoned in part because it is not bright enough, and it is broken down too quickly in the body by ascorbate -- vitamin C.

"This ORCA is a metal-free agent that is compatible with current MRI techniques, is less toxic to the body and is highly biodegradable. Unfortunately, on its own, it's not very bright, and it's so biodegradable that it's impractical to use," Gassensmith said.

MRI Homepage