Customised microscopic magnets injected into the body could enable Magnetic Resonance imaging (MRI) scans to be viewed in colour.

Researchers at the National Institute of Standards and Technology (NIST) and National Institutes of Health (NIH) believe the micromagnets also have the potential to be used as ‘smart tags’, to identify certain cells and tissues.

Unlike the chemical solutions currently used as image enhancing contrast agents in MRI, the micromagnets rely of a precisely turnable feature – their physical shape – to adjust the radio frequency (RF) signals used to create images. The RF signals can be converted in a range of optical colours by computer, so different magnets designed to appear as different colours, could be coated to attach to different cell types, such as cancerous Versus normal. The cells could then be identified by tag colour.

Each micromagnet consists of two round vertically stacked magnetic discs a few millimetres in diameter that are separated by a small open gap. Initially these discs were made of nickel, which is toxic, but was selected for its ease of use. Study author Gary Zabow, explained that these discs could be made of other non-toxic, and is already approved for use in certain medical applications. Only very low concentrations of the magnets would be needed in the body to enhance MRI images.

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. It is these signals that are used to create the images. This ‘open sandwich’ design allows the movement of diffusion of water through the micromagnet, producing a signal that could be a thousand times stronger than that produced by a similarly sized, but stationary volume of water. The diffusion effectively increases local MRI sensitivity, which in a future clinical setting could lead to practical benefits such as faster imaging, images that are richer in information, or reduced dose requirements for these contrast agents.

Researchers create a customised 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. The micromagnets can also 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.

While much excitement surrounds the development of these micromagnets, extensive further engineering and testing, including clinical studies is needed before they can be used in people undergoing MRI exams.