Optical magnetic field sensors provide alternative for MRI systems

September 24, 2018 // By Rich Pell
Researchers at the University of Arizona, Tucson, have developed a light-based technique for measuring very weak magnetic fields, such as those produced from neurons firing in the brain and heart.

Fabricated using optical fibers and a newly developed polymer-nanoparticle composite that is sensitive to magnetic fields, the sensors can detect the brain's magnetic field, which is 100 million times weaker than the magnetic field of earth. The inexpensive and compact magnetic sensors, say the researchers, could offer an alternative to the large and costly magnetic resonance imaging (MRI) systems currently used to map brain activity by avoiding the expensive cooling or electromagnetic shielding required by MRI machines.

"A portable, low-cost brain imaging system that can operate at room temperature in unshielded environments," says researcher member Babak Amirsolaimani, "would allow real-time brain activity mapping after potential concussions on the sports field and in conflict zones where the effect of explosives on the brain can be catastrophic."

In addition to brain activity, the researchers showed that the new sensor can detect the weak magnetic pattern of a human heartbeat - demonstrating the technology's potential as a simple replacement for electrocardiography, or ECG, tests commonly performed to detect heart problems - and has the capability to detect magnetic fluctuations that change every microsecond from an area as small as 100 square microns.

“The all-optical design of the sensor means it could be fabricated inexpensively on a silicon photonics chip," says Amirsolaimani, "making it possible to produce a system that is almost as small as the sensor's 10-micron-diameter optical fiber. Multiple sensors could then be used together to provide high spatial resolution brain mapping."

The new sensors, say the researchers, could help scientists better understand the activity of the brain and diseases of the brain such as dementia and Alzheimer's. In addition, they may also be useful for measuring the magnetic fields used to predict volcanic eruptions and earthquakes, identify oil and minerals for excavation, and detect military submarines.

The sensors work by taking advantage of the fact that a magnetic field causes the polarization of light to rotate, with the degree of rotation

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