Researchers demonstrate nanoscale MRI technique

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A team from the University of Illinois at Urbana-Champaign and Northwestern University has devised a nuclear magnetic resonance imaging (MRI) technique that delivers a roughly 10nm spatial resolution.

This is said to represent a significant advance in MRI sensitivity as modern MRI techniques commonly used in medical imaging yield spatial resolutions on the millimetre length scale, with the highest-resolution experimental instruments giving spatial resolution of a few micrometers.

‘This is a very promising experimental result,’ said U. of I. physicist Raffi Budakian, who led the research. ‘Our approach brings MRI one step closer in its eventual progress toward atomic-scale imaging.’

MRI is used widely in clinical practice to distinguish pathologic tissue from normal tissue. It is non-invasive and harmless to the patient, using strong magnetic fields and non-ionising electromagnetic fields in the radio frequency range, unlike CT scans and traditional X-rays, which use more harmful ionising radiation.

MRI uses static and time-dependent magnetic fields to detect the collective response of large ensembles of nuclear spins from molecules localised within millimetre-scale volumes in the body. Increasing the detection resolution from the millimetre to nanometre range would be a significant technological advance.

According to a statement, the new technique introduces two unique components to overcome obstacles to applying classic pulsed magnetic resonance techniques in nanoscale systems. First, a novel protocol for spin manipulation applies periodic radio-frequency magnetic field pulses to encode temporal correlations in the statistical polarisation of nuclear spins in the sample. Second, a nanoscale metal constriction focuses current, generating intense magnetic field-pulses.

In their proof-of-principal demonstration, the team used an ultrasensitive magnetic resonance sensor based on a silicon nanowire oscillator to reconstruct a two-dimensional projection image of the proton density in a polystyrene sample at nanoscale spatial resolution.

‘We expect this new technique to become a paradigm for nanoscale magnetic-resonance imaging and spectroscopy into the future,’ said Budakian. ‘It is compatible with and can be incorporated into existing conventional MRI technologies.’

The team’s paper, Nanoscale Fourier-Transform Magnetic Resonance Imaging, is published in Physical Review X.