Copenhagen scientist develops optical magnetometer to spot flaws in MRI scans...

07 May 2024

...while WUSL’s “optical barcodes” offer new applications in biomedical diagnostics.

Hvidovre Hospital, Copenhagen, Denmark, has developed what it is calling “the world’s first prototype of a sensor capable of detecting errors in MRI scans” using laser light and gas. The new sensor, created by a researcher at the University of Copenhagen and the hospital, can do what is considered impossible for current electrical sensors – promising MRI scans that are better, cheaper and faster.

The strong magnetic fields inside MRI scanners have fluctuations that create errors and disturbances in scans. Consequently, these expensive machines (operating costs are typically hundreds of euros per hour) must be calibrated regularly to reduce errors.

There are also certain special scanning methods, which cannot be achieved in current practice. Among them, spiral sequencing, which could reduce scanning time, for example, when diagnosing blood clots, sclerosis and tumors. Spiral sequencing would also be an attractive tool in MRI research, which could provide researchers with information about brain diseases. But due to the highly unstable magnetic field, performing such scans is not currently an option.

A new invention hopes to eliminate this problem. A researcher from the Niels Bohr Institute and Danish Research Centre for Magnetic Resonance (DRCMR) has developed a sensor that uses laser light moving in optical cables and a small glass container filled with gas.

“First we demonstrated that it was theoretically possible, and now we have proven that it can be done in practice,” said Hans Stærkind, a postdoc at the Niels Bohr Institute and DRCMR at Hvidovre Hospital. Stærkind is the main architect behind the sensor and device that comes with it.

He continued, “In fact, we now have a prototype that can basically make the measurements needed without disturbing the MRI scanner. It needs to be developed more and fine-tuned, but has the potential to make MRI scans cheaper, better and faster – although not necessarily all three at once.”

“An MRI scanner can already produce incredible images if one takes their time. But with the help of my sensor, it is imaginable to use the same amount of time to produce even better imagery – or spend less time and still get the same quality as today. A third scenario could be to build a cheaper scanner that, despite a few errors, could still deliver decent image quality with the help of my sensor,” said Stærkind.

How it works

The prototype works using a device that sends laser light through fiber optic cables and into four sensors located in the scanner. Within the sensors, the light passes through a small glass container containing cesium gas, which absorbs the light at the optimal light frequencies.

“When the laser has just the right frequency while passing through the gas, there is a resonance between the waves of light and electrons in the cesium atoms. But the frequency at which this happens changes when the gas is exposed to a magnetic field. In this way, we can measure the strength of the magnetic field by finding out what the right frequency is,” the researcher said.

As disturbances in an MRI scanner's ultra-powerful magnetic field occur, the prototype sensor maps exactly where they are occurring and by what strength the field has changed. In the near future, this could mean that disturbed and faulty images could be corrected and subsequently made more accurate and useful.

The prototype is currently housed at DRCMR at Hvidovre Hospital in Copenhagen, which is also where the idea was conceived. “The original idea came from my supervisor here at DRCMR, Esben Petersen, who is unfortunately no longer with us. He saw huge potential in developing a sensor based on lasers and gas that would be able to measure the magnetic fields without disturbing them,” said Stærkind.

“Once the prototype has been refined into a 2.0 version and its qualities documented with data from actual scans here at the hospital, we will see where this goes. It certainly has the potential to improve MRI scans in a unique way that can benefit doctors and, not least, patients.”

‘Optical barcodes’ expand range of high-resolution sensing

Washington University in St. Louis has announced the development of what it calls “optical barcodes”, which it says will expand the current range of high-resolution sensing. Development team Lan Yang and Jie Liao say their optical barcodes for multimode sensing have potential applications in biomedical diagnostics, environmental monitoring, chemical sensing.

The same geometric quirk that lets visitors murmur messages around the circular dome of the whispering gallery at St. Paul’s Cathedral in London or across St. Louis Union Station’s whispering arch also enables the construction of high-resolution optical sensors. Whispering-gallery-mode (WGM) resonators have been used for decades to detect chemical signatures, DNA strands and even single molecules.

In the same way that the architecture of a whispering gallery bends and focuses sound waves, WGM microresonators confine and concentrate light in a tiny circular path. This enables WGM resonators to detect and quantify physical and biochemical characteristics, making them ideal for high-resolution sensing applications in fields such as biomedical diagnostics and environmental monitoring. However, the broad use of WGM resonators has been limited by their narrow dynamic range as well as their limited resolution and accuracy.

‘Transformative approach’

In a recent study, published in IEEE Xplore, Lan Yang, the Edwin H. & Florence G. Skinner Professor, and Jie Liao, a postdoctoral research associate, both in the Preston M. Green Department of Electrical & Systems Engineering in the McKelvey School of Engineering at Washington University in St. Louis, demonstrate a transformative approach to overcome these limitations: optical WGM barcodes for multimode sensing.Liao and Yang’s technique allows simultaneous monitoring of multiple resonant modes within a single WGM resonator, considering distinctive responses from each mode, vastly expanding the range of measurements achievable.

WGM sensing uses a specific wavelength of light that can circulate around the perimeter of the microresonator millions of times. When the sensor encounters a molecule, the resonant frequency of the circulating light shifts. Researchers can then measure that shift to detect and identify the presence of specific molecules.

“Multimode sensing allows us to pick up multiple resonance changes in wavelength, rather than just one,” Liao explained. “With multiple modes, we can expand optical WGM sensing to a greater range of wavelengths, achieve greater resolution and accuracy, and ultimately sense more particles.”

Liao and Yang found the theoretical limit of WGM detection and used it to estimate the sensing capabilities of a multimode system. They compared conventional single-mode with multimode sensing and determined that while single-mode sensing is limited to very narrow range – about 20 pm, constrained by the laser hardware – the range for multimode sensing is potentially limitless using the same setup.

“More resonance means more information,” Liao said. “We derived a theoretically infinite range, though we’re practically limited by the sensing apparatus. In this study, the experimental limit we found was about 350 times larger with the new method than the conventional method for WGM sensing.”

Commercial applications of multimode WGM sensing could include biomedical, chemical and environmental uses, Yang said. In biomedical applications, for instance, researchers could detect subtle changes in molecular interactions with unprecedented sensitivity to improve disease diagnosis and drug discovery.In environmental monitoring, with the capability to detect minute changes in environmental parameters such as temperature and pressure, multimode sensing could enable early warning systems for natural disasters or facilitate monitoring pollution levels in air and water.