Micromagnets Show Promise as Colorful 'Smart Tags' for MRI

Microscopic magnets (above left), designed and tested in a joint NIST/NIH project, might one day be injected into the body to add color and “smart tag” capability to magnetic resonance imaging for medical diagnosis and research. The image on the right shows light scattering from grids of magnets on a wafer where they were made using conventional microfabrication techniques. Credit: G. Zabow, NIST/NIH View hi-resolution of image on left | View hi-resolution of image on right

Customized microscopic magnets might one day be injected into the body to add color to magnetic resonance imaging (MRI) while enhancing sensitivity and the amount of information provided by images researchers at the National Institute of Standards and Technology (NIST) and National Institutes of Health (NIH) report. The new micromagnets also could act as “smart tags,” identifying particular cells, tissues or physiological conditions for medical research or diagnostic purposes.

As described in the June 19 issue of Nature,* the NIST and NIH investigators have demonstrated the proof of principle for a new approach to MRI. Unlike the chemical solutions now used as image-enhancing contrast agents in MRI, the NIST/NIH micromagnets rely on a precisely tunable feature—their physical shape—to adjust the radiofrequency (RF) signals used to create images. The RF signals then can be converted into a rainbow of optical colors by computer. Sets of different magnets designed to appear as different colors could, for example, be coated to attach to different cell types, such as cancerous versus normal.

“Current MRI technology is primarily black and white; this is like a colored tag for MRI,” says lead author Gary Zabow, who designed and fabricated the microtags at NIST and, together with colleagues at the National Institute of Neurological Disorders and Stroke, part of NIH, tested them on MRI machines.

The microtags would need extensive further engineering and testing, including clinical studies, before they could be used in people. The initial prototypes were made of nickel, which is toxic but relatively easy to work with, but Zabow says they could be made of other magnetic materials, such as iron, which is considered non-toxic and is already approved for use in certain medical agents. Only very low concentrations of the magnets would be needed in the body to enhance MRI images.

Each micromagnet consists of two round vertically stacked magnetic discs a few micrometers in diameter separated by a small open gap in between. Researchers create a customized magnetic field for each tag by making it from particular materials and tweaking the geometry, perhaps by widening the gap between the discs or changing the discs’ thickness or diameter. As water in a sample flows between the discs, protons acting like twirling bar magnets within the water’s hydrogen atoms generate predictable RF signals—the stronger the magnetic field, the faster the twirling—and these signals are used to create images. The magnets could make medical diagnostic images as information-rich as the optical images of tissue samples now common in biotechnology, which already benefits from a variety of colored markers such as fluorescent proteins and tunable quantum dots.

NIH support for Zabow’s work was funded by the National Institute of Biomedical Imaging and Bioengineering (NIBIB) through the NIST/NIH-NIBIB National Research Council Joint Associateship Program. NIH has filed a provisional patent application on the micromagnets.

To read more about micromagnets, see “NIST/NIH Micromagnets Show Promise as Colorful ‘Smart Tags’ for Magnetic Resonance Imaging.”

* G. Zabow, S. Dodd, J. Moreland, A. Koretsky. 2008. Micro-engineered local field control for high-sensitivity multispectral MRI. Nature. June 19.