Magnets colour MRI scans

Microscopic magnets injected into the body might one day allow physicians to view magnetic resonance imaging (MRI) scans in colour.

According to researchers at the US National Institute of Standards and Technology (NIST) and National Institutes of Health (NIH), the micromagnets also could act as 'smart tags', to identify particular cells.

Unlike the chemical solutions now used as image-enhancing contrast agents in MRI, the NIST/NIH micromagnets have a precisely tunable feature - their physical shape - which allows them to return specific radiofrequency (RF) signals to the computers used in MRI equipment.The computer would then convert these signals into specific colours.

The magnets could also be coated so that they would attach themselves to different cell types, such as cancerous cells, allowing those cells to be highlighted on a MRI scan.

'Current MRI technology is primarily black and white; this is like a coloured tag for MRI,' said 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 said 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 micrometres in diameter, separated by a small open gap in between.

As water in a sample flows between the discs, protons acting like spinning bar magnets within the water’s hydrogen atoms generate the RF signals that are then picked up by the MRI machine.

To tailor a set of magnets for a specific purpose, the NIST researchers can make the magnetic field of the discs stronger, which then increases the speed of the spinning protons and changes the frequency of the RF signal that is emitted.

This customisation of the magnets can be achieved by making them from different materials,  tweaking their geometry by widening the gap between the discs, or changing the discs’ thickness or diameter.

NIH has filed a provisional patent application on the micromagnets.