Researchers at the Massachusetts Institute of Technology have developed an alternative to gadolinium-based contrast agents for MR exams.
The new iron oxide nanoparticles may be safer for patients with impaired kidney function.
About a third of the 60 million MR procedures performed annually use contrast agents that usually contain gadolinium, according to MIT. Studies have shown that in rare cases gadolinium can cause a potentially fatal condition called nephrogenic systemic fibrosis.
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Recent research has shown that gadolinium can accumulate in the brain
, but to date it hasn’t been proved to cause any harmful effects. The FDA is currently investigating whether this build up in the brain is harmful.
The MIT researchers found that similar MR contrast can be produced with small iron oxide nanoparticles that have been treated with a zwitterion coating. Zwitterions are molecules that have areas of positive and negative electrical charges that cancel out and make them neutral.
Some contrast agents generate negative or dark areas in the MR image and other produce positive or light areas. The agents that produce light areas contain gadolinium, and iron oxide particles have mostly been used as dark contrast agents.
However, the iron oxide inorganic core is small enough to produce a noticeable positive contrast in MR. Radiologists prefer positive agents because it can be difficult to differentiate certain imaging artifacts and internal bleeding when using negative agents.
Unlike gadolinium-based contrast agents, the coated iron oxide can clear from the kidney quickly and not accumulate. The combination of the very small iron oxide core and the ultrathin ligand shell yields a total hydrodynamic diameter of 4.7 nanometers, which is below the 5.5-nanometer renal clearance threshold.
Initial tests have shown that the iron oxide particle is an effective contrast agent. Going forward, the researchers will perform more toxicology testing to demonstrate the particle’s safety and continue to improve the characteristics of the material.