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Metamaterial-Enhanced Imaging Technique Could Reduce Acquisition Time

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ST. PETERSBURG, Russia and LEIDEN, Netherlands, June 20, 2017 — A hybrid metasurface structure, composed of a 2D metamaterial surface and a high permittivity dielectric substrate, has been shown to enhance the performance of an ultra-high field MRI scanner. The ultrathin structure could potentially be used to reduce image acquisition time or, alternatively, to facilitate higher resolution images.

Metamaterial-enhanced MRI technique, ITMO and Leiden University Medical Center.
Metasurface structure and application. Courtesy of ITMO University.

Due to its intrinsically low signal-to-noise ratio (SNR), an MRI scan takes longer to acquire than a computed tomography or ultrasound scan. Use of large metamaterial structures would require the MRI coil array to be placed some distance away from the body, resulting in a loss of sensitivity and cancelling out much of the metamaterial’s performance-enhancing value.

Taking a novel approach to reducing image acquisition time, researchers from ITMO University and Leiden University Medical Center designed a thin, flexible metasurface that could be fully integrated into a multi-element receive array. Their compact metasurface can be placed between the patient and the close-fitting receive coil array used in clinical MRI scans.

Metamaterial-enhanced MRI technique, ITMO and Leiden University Medical Center.
A patient in MRI scan modified by metasurface. Courtesy of ITMO University.

Researchers formed the metasurface using thin conductor strips coupled to a flexible high permittivity pad. The metasurface can fit into a commercial 32-channel receive array.

Use of the metasurface was demonstrated in a human brain MRI and localized MR spectroscopy at 7 Tesla, where the focus was on using the metasurface to produce a local increase in the SNR in the occipital cortex.

The metasurface structure, when placed between the patient and the receive coil arrays, enhanced the SNR in the region of interest.

“We placed such a metasurface under the patient's head, [and] after that the local sensitivity increased by 50 percent. 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,” said Leiden University researcher Rita Schmidt. 

Metamaterial-enhanced MRI technique, ITMO and Leiden University Medical Center.

MRI image made with and without metasurface. Courtesy of ITMO University.

“This ratio limits the MRI sensitivity and duration of the procedure,” said ITM researcher Alexey Slobozhanyuk. “Conventionally, if now an examination takes twenty minutes, it may only need ten in the future. If today hospitals serve 10 patients a day, they will be able to serve 20 with our development.” 

The researchers believe the metasurface could also be used to increase the image resolution.

“The size of voxels, or 3D pixels, is also limited by the signal-to-noise ratio. Instead of accelerating the procedure, we can adopt an alternative approach and acquire more detailed images," said Leiden University professor Andrew Webb.

According to the research team, until now no one has shown integration of metamaterials into close-fitting receive arrays because their dimensions were much too large. The novel ultrathin design of the metasurface could help solve this issue.

“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 metasurface is appropriately coupled,” said Schmidt.

The research was published in Scientific Reports (doi: 10.1038/s41598-017-01932-9).
Jun 2017
Research & TechnologyeducationEuropeimagingopticsmedicalmedicinematerialsmetamaterials

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