Multicolor MRI could let doctors watch diseases at work

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Customized microscopic magnets that may be injected into the body could add color to MRI, while also potentially enhancing sensitivity and the amount of information provided by images, according to researchers at the National Institute of Standards and Technology (NIST) and National Institutes of Health (NIH).

The new micromagnets also could act as “smart tags” identifying particular cells, tissues, or physiological conditions, for medical research or diagnostic purposes.

The study, published in the June 19 issue of Nature, has demonstrated the proof of principle for a new approach to MRI, according to NIST and NIH investigators.

“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.

If multicolor MRI lives up to its promise, it could provide visual information at the level of genes, proteins and other molecules. Researchers hope that this molecular imaging will eventually become part of personalized medicine, allowing doctors to literally see the processes underlying an individual patient's inflammation or tumor growth and then prescribe the right therapy with less guesswork, according to Technology.

The micromagnets, which would need extensive further engineering and testing, including clinical studies, before they could be used in people undergoing MRI exams, adjust the radio-frequency (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. The cells then could be identified by tag color, according to researchers.

The magnets used in the NIST/NIH studies were made of nickel, but Zabow says they could be made of other magnetic, non-toxic materials, such as iron, which 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, he noted.

Researchers create a customized magnetic field for each tag by making it from particular materials and by widening the gap between the micromagnets’ discs or changing the discs’ thickness or diameter. As water in a sample flows between the discs, protons act like twirling bar magnets within the water’s hydrogen atoms to generate predictable RF signals, Technology reported.

Using water to move through the micromagnet effectively increases local MRI sensitivity. Additionally, the magnets can be designed to have more tunable properties than conventional injectable MRI contrast agents, which are chemically synthesized whereas the new micromagnets are microfabricated, the researchers noted.

This allows for greater control and range of the modified magnetic field, greatly enhancing sensitivity, according to the researchers. Each micromagnet potentially could be individually detected for imaging purposes and also could be designed to be turned on and off by, for example, filling the gap between the discs to block water passage. The gap could be filled with something that dissolves when exposed to certain substances or conditions, Zabow added.

The micromagnets can be made using conventional microfabrication techniques and are compatible with standard MRI hardware. Advanced lithography techniques of the kind used to make sophisticated computer chips might be used to make the tags even smaller, approaching the nanometer scale, according to the paper.

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, the researchers concluded.

NIH has filed a provisional patent application on the micromagnets, according to a press release.

The National Institute of Biomedical Imaging and Bioengineering (NIBIB) through the NIST/NIH-NIBIB National Research Council Joint Associateship Program provided funding for Zabow’s work.