Because of its strong paramagnetic properties, gadolinium alters the relaxation of hydrogen atoms when it's nearby. Contrast agents containing gadolinium can be designed to collect preferentially in tumors, thus enhancing the contrast between the tumor and the surrounding tissue. The contrast agent's ability to alter the relaxation of hydrogen atoms is expressed as "relaxivity", which accounts for the relaxation time and the concentration of gadolinium in the tissues.

The high relaxivity of the gadolinium-nano diamond compound can be partly attributed to its ability to attract water, which helps boost the MRI signal. "If you look at the shape of a nano diamond, it's like a soccer ball but more angular around the faces," Ho says. "It's not totally round." The different faces have alternating positive and negative charges, which helps to orient water molecules in such a way that they create a tight shell of water around the nanodiamond.

The researchers tested the gadolinium-nano diamond on different types of cells in the lab and did not find evidence of toxicity. The next step, Ho says, is to test the compound's safety and effectiveness as a contrast agent in animals. "We're excited to see what kind of increased performance we can get," Ho says.

"I think it's a very interesting system," says Kenneth N. Raymond, professor of chemistry at the University of California at Berkeley. "They've obviously got a one order of magnitude increase in relaxivity that's quite significant." Many researchers have tried to attach gadolinium ions to high molecular weight compounds, like proteins and dendrimers, he says. "The little nano diamond, as far as I know, is quite novel, and, I think, a very clever thing to do."

Currently, radiologists need to inject what amounts to several grams of gadolinium into a patient to get good contrast on an MRI. By increasing the sensitivity of the contrast agent ten-fold, "you could use one-tenth as much gadolinium," Raymond says. "There's a lot of concern in the clinic for certain classes of patients about gadolinium toxicity. Toxicity is very closely connected to dose."