Meta MRI: Scan booster

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  • Published: Jun 1, 2017
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: Meta MRI: Scan booster

Meta is better

Metamaterial in MRI - near field magnetic and electric field distributions. Top: cutaway schematic showing setup. Middle: in vivo experiment. Bottom: Sketch of the hybrid metasurface

A meta material can boost the local sensitivity of magnetic resonance imaging (MRI), according to work by researchers from Leiden University Medical Center in the Netherlands and ITMO University Russia who have demonstrated the system with in vivo scanning of people for the first time. The meta surface comprises thin resonant strips arranged periodically. These are placed under the patient's head in the case of a head scan and generates much stronger signals from the scan of the brain. Writing in the journal Scientific Reports, the team explains that their meta surface setup can potentially reduce image acquisition time and so reduce the length of time the patient must remain still in the scanner. Conversely, the same system could be used to acquire higher resolution images for better disease diagnosis.

MRI is, of course, widely used in medicine and biomedical research offering information on structural and functional damage in neurological, cardiovascular, musculoskeletal conditions, and in cancer diagnostics. However, magnetic resonance has an intrinsically low signal-to-noise ratio than other phenomenon one might use to scan a person or their internal organs. MRI scans take much longer to acquire than computed tomography or ultrasound scans, but they do provide much greater and more subtle details and so there is a balance to be met in terms of the patience of patients and the benefits they will receive. Patients must remain motionless during the scan, in what is essentially a rather confined space and an MRI scan in a hospital might take up to an hour. The knock-on effect is that there is always a long queue for MRI, whereas throughput for faster scanning techniques can be much higher.

On the surface

"We placed the meta surface under the patient's head, after that the local sensitivity increased by 50%. This allowed us to obtain higher image and spectroscopic signals from the occipital cortex. Such devices could potentially reduce the duration of MRI studies and improve its comfort for subjects", says Leiden's Rita Schmidt. Alexey Slobozhanyuk, a research fellow in the Department of Nanophotonics and Metamaterials at ITMO explains that the meta surface gives them a boost to the signal to noise ratio and so avoids the need for repeated scans, which are then added together. "Conventionally, if now an examination takes twenty minutes, it may only need ten in the future," he explains. "If today hospitals serve ten patients a day, they will be able to serve twenty with our development."

Faster versus fitter

Conversely, the same system could be used to increase the resolution of the images obtained. "The size of voxels, the 3D pixels from an MRI scan, is also limited by the signal to noise ratio. So, instead of reducing acquisition times, the approach could be used to obtain much more detailed images, according to project leader Andrew Webb. Until now, the use of meta materials integrated with the close-fitting receive arrays has not been demonstrated. The new ultra-thin design of the meta surface solves the issues of how to fit the system into existing MRI scanner architecture.

"Our technology can be applied for producing metamaterial-inspired ultra-thin devices for many different types of MRI scans, but in each case, one should firstly carry out a series of computer simulations as we have done in this work. One needs to make sure that the meta surface is appropriately coupled", adds Schmidt.

Related Links

Sci Rep 2017, online: "Flexible and compact hybrid metasurfaces for enhanced ultra high field in vivo magnetic resonance imaging"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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