Physicists inch toward atomic-scale MRI

Researchers are improving the first nanoscale MRI technique developed at MIT in 2009 in the hopes of imaging such biological samples as viruses at extremely high resolution.

This illustration of the experimental setup shows the two unique components of the novel MRI technique that produced nanoscale resolution. University of Illinois

A team of physicists at the University of Illinois at Urbana-Champaign and Northwestern University is working on a novel MRI technique that has achieved nanoscale resolution -- meaning scientists could soon view biological samples such as influenza viruses very clearly.

The experimental result brings MRI one step closer to atomic-scale imaging, says lead researcher Raffi Budakian of the University of Illinois, who reports his findings in the journal Physical Review X. "Imagine a 3D image slice-by-slice of an influenza virus and then looking at all the chemical components with nanometer-scale resolution. That's our dream. It provides a toolset for biology that doesn't yet exist."

Magnetic resonance imaging has been around since the '70s and is a widely-used diagnostic tool for a wide range of diseases and disorders. It offers a 3D glimpse of living tissue that is both noninvasive and safe -- it uses strong magnetic field and non-ionizing electromagnetic fields in the radio frequency range instead of the more harmful ionizing radiation in CT scans and traditional X-rays. Better yet, it is far richer than X-ray, which just looks at how light scatters, but doesn't distinguish density -- such as water from fat or hydrogen from carbon. MRI does, providing a view of, say, healthy versus cancerous tissue.

But its great limitation has been scale; until nanoscale-level MRI was first achieved at MIT in 2009, the technique couldn't image anything below several cubic micrometers.

Now, Budakian's team has been able to take that achievement a step further with a few key improvements to the technique -- overcoming obstacles to applying conventional MRI techniques to nanoscale systems -- and he says his approach can be incorporated into existing MRI tech.

To demonstrate the advance, the team used an ultrasensitive magnetic resonance sensor based on a silicon nanowire oscillator to reconstruct a 2D projection image of the proton density of a polystyrene sample at nanoscale.

Budakian says one of the next hurdles is how to handle nanometer-scale biological samples at the temperature they need to be using this MRI technique: "It's a low-temperature environment; we have to cool things down to cryogenic temperatures. And there is a way to prep biological materials to survive that, but it's by no means trivial and is something we'll have to think about moving forward. It's by no means guaranteed that the image will be at all relevant to what's going on inside someone's body."

He adds that, while the speed of future advances depends to a large degree on funding, he hopes to demonstrate spatial resolutions between one and three nanometers in the next few years.

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