New “Intelligent” Metamaterial Significantly Improving MRIs While Cutting Costs

Researchers from Boston University have recently created a new metamaterial that has shown promise in making the magnetic resonance imaging (MRI) process faster, safer, and more accessible to patients. This material costs under $10 to create and could potentially revolutionize MRI imaging. A paper published on October 30 in Advanced Materials detailed the BU team’s work with this technology.

In addition to being costly and exposing patients to radiation, the MRI process can be extremely time-consuming, often taking nearly an hour for a single scan. For this reason, researchers have been experimenting with ways to cut down the time required for each MRI without reducing the image quality.

To address this, Xin Zhang, a BU College of Engineering professor of mechanical engineering and a Photonics Center professor, and a research team including Stephan Anderson, a Boston Medical Center radiologist and BU School of Medicine professor of radiology, and Xiaoguang Zhao, an MED assistant research professor of radiology, have been experimenting with metamaterials.

“An MRI’s magnetic field is many thousands of times stronger than the Earth’s magnetic field,” explained Zhao. “A precisely orchestrated series of higher-energy radio waves are sent into the human body, and the tissues emit lower-energy radio waves that are received by the MRI to produce an image.”

MRI quality depends on the signal-to-noise ratio (SNR), with a higher SNR indicating better image quality. Increasing the magnetic field is the most direct way to enhance the SNR, however, this increases the cost and complexity of the imaging process. In addition, this increased magnetic field increases the risk the patient assumes, with increased heat from this radiation potentially affecting implanted medical devices.

A Metamaterial Solution

Zhang and colleagues have created a novel magnetic metamaterial that is placed over the region of interest to bolster the energy emitted by the patient’s body and increase SNR. This magnetic metamaterial consists of simple copper wiring and plastic and was discussed in a March 2019 publication of Nature’s Communications Physics.

Alongside Anderson, Zhao, and other team members, Zhang has now enhanced the metamaterial to become “intelligent” in the sense that it selectively boosts low-energy emissions from the patient’s body. This material turns itself off during the millisecond bursts of energy from the radiation machine.

This intelligent metamaterial increases the SNR 10-fold, which significantly amplifies image quality and reduces scan time. This opens up an improved, cost-efficient way to obtain MRI images, as per Zhang.

“Shortening MRI examinations is paramount to maximizing the capacity,” said Anderson. “Not to mention revenue, as well as the overall patient experience of this powerful imaging technology.”

“The intelligent metamaterial consists of an array of metallic helical resonators closely packed with [a passive sensor],” added Zhao. “When the high-energy radio waves are coming in, the metamaterial detects the high energy level and ‘turns off’ the resonance automatically. With low-energy radio excitation, the metamaterial [turns on] the resonance and enhances the magnetic component of the radio wave.”

That short time frame where the material turns off allows physicians to use the metamaterial to enhance the energy sent back to the MRI machine. This feature also reduces the patient’s exposure to radiation, enhancing the safety of this imaging technique.

“We can now build smart materials that can interact with radio waves intelligently, enhancing the wanted signal while letting the unwanted signal go,” said Zhang.

Zhang and colleagues estimate that the metamaterial will cost less than $10 to create. Although the prototype is a flat, thick layer, the team plans to create a flexible, thin sheet that is better suited for clinical use.