NIST Uses Nanomagnets to Enhance Medical Imaging

February 19, 2007 // Published as a news service by IHS

According to a new report from researchers at the National Institute of Standards and Technology (NIST), molecular nanomagnets are a new class of MRI contrast agents that may offer significant advantages, including versatility in design, over the compounds used today.

Researchers resolved a debate in the literature by showing that iron-containing magnets just 2 nanometers (nm) wide, dissolved in water, provide reasonable contrast in non-clinical MRI images, as long as the nanomagnet concentration is below a certain threshold.

Previous studies from other research groups found conflicting conclusions on the utility of molecular nanomagnets for MRI, but without accounting for concentration. NIST scientists, making novel magnetic measurements, were able to monitor the molecules' decomposition and magnetic properties as the composition was varied.

The injectable dyes used as MRI contrast agents today are of two types. Magnetic ions, which alter the nuclear properties of hydrogen in water, offer the advantage of consistent identical design but provide low contrast.

The second category encompasses particles of thousands of atoms or crystals, which alter local magnetic fields. They provide contrast variation in a larger region, but have irregular designs and magnetic properties that are difficult to control.

By comparison, molecular nanomagnets can be designed to have consistent properties and high contrast. They might be modified to act as "smart" materials whose contrast could be turned on only when bonded to a target molecule or cell.

Researchers said toxicity is not believed to be an issue, because iron is naturally found in the body and other studies have found that these materials are non-toxic at the concentrations used in MRI.

NIST works with Florida State University to make single-molecule magnets less than 5 nm in diameter, and works with the University of Colorado at Boulder to make nanocrystals in the 10-50 nm range. The agency is pioneering methods for manipulating and measuring the magnetic properties of these compounds and is developing instrumentation for understanding how contrast agents work and how to control contrast properties.

Researchers correlate the measured properties to the observed MRI response under non-clinical conditions using imagers at The Children's Hospital in Denver. The information gained is fed back into recipes for making even better nanomagnets.

Source: National Institute of Standards and Technology (NIST).