Nanomagnets Used To Enhance MRI

Nanoscale magnets comprised of iron-containing molecules may soon be used to improve the contrast between healthy and diseased tissue in magnetic resonance imaging (MRI)--as long as the concentration of nanomagnets is precisely controlled.

Molecular nanomagnets are a new class of MRI contrast agents that may offer significant advantages, such as versatility in design, over the compounds currently used. Contrast agents are utilized to highlight different tissues in the body or to help distinguish between healthy and diseased tissue.

Researchers from the U.S. National Institute of Standards and Technology (NIST; Gaithersburg, MD, USA) and their collaborators are currently working with two universities and a hospital to design, produce, and evaluate nanomolecules that might make MR imaging more powerful and easier to perform. The new study resolves a debate in the literature by showing that iron-containing magnets only 2 nm-wide, dissolved in water, can indeed provide accurate contrast in non-clinical MRI images--as long as the nanomagnet concentration is below a specific threshold. Earlier studies by other researchers had reached contradictory conclusions on the utility of molecular nanomagnets for MRI, but without accounting for concentration. NIST scientists, making unique magnetic measurements, were able to monitor the molecules' decomposition and magnetic properties as the composition was varied.

The injectable dyes currently used as MRI contrast agents are of two types. Magnetic ions, which change the nuclear characteristics of hydrogen in water, provide 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 hard to control. By comparison, molecular nanomagnets can be devised to have consistent properties and high contrast. Furthermore, they might be modified to act as "smart” materials whose contrast could be turned on only when bonded to a target molecule or cell. Toxicity should not be a problem, according to the researchers, 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 researchers are working with Florida State University (Tallahassee, USA) to make single-molecule magnets less than 5 nm in diameter, and are also collaborating with investigators from the University of Colorado (Boulder, USA) to produce nanocrystals in the 10-50 nm range.
The study will be reported in an upcoming issue of the journal Polyhedron.





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