MIT researchers develop MRI sensor to detect light deep in the brain

Researchers from MIT have developed a specialized MRI sensor capable of detecting light deep within tissues, including the brain, MIT News said.

The sensor has significant potential for mapping light emitted by optical fibers implanted in the brain, such as those used in optogenetic experiments to stimulate neurons. With further development, it could be utilized to monitor patients undergoing light-based therapies for cancer.

The ability to image light in deep tissues has long been a challenge due to light absorption and scattering. However, the MIT team said it overcame this obstacle by designing a sensor that converts light into a magnetic signal detectable by magnetic resonance imaging (MRI).

"We can image the distribution of light in tissue, and that's important because people who use light to stimulate tissue or to measure from tissue often don't quite know where the light is going, where they're stimulating, or where the light is coming from. Our tool can be used to address those unknowns," said the senior author of the study, Alan Jasanoff, an MIT professor of biological engineering, brain and cognitive sciences, and nuclear science and engineering.

The study, published in Nature Biomedical Engineering, was led by Jacob Simon, a recent Ph.D. graduate, and Miriam Schwalm, a postdoctoral researcher at MIT. The research team also included Johannes Morstein and Dirk Trauner from New York University. 

The researchers created a magnetic sensor that responds to light locally, overcoming the limitations of optical imaging, the MIT news report said. With this, researchers encapsulated magnetic particles in liposomes, which are nanoparticles made from light-sensitive lipids. When exposed to specific wavelengths of light, these liposomes become permeable to water, allowing the magnetic particles inside to interact with water and generate a signal detectable by MRI. The researchers named these particles liposomal nanoparticle reporters (LisNR).

According to the report, the LisNR particles can switch between permeable and impermeable states depending on the light they are exposed to. In the study, the researchers demonstrated the particles' response to ultraviolet light and blue light, and they also showed the particles' ability to respond to other light wavelengths. To test the sensors, researchers injected the particles into the brains of rats, specifically targeting the striatum, a region involved in movement planning and reward response. They successfully mapped the distribution of light emitted by an optical fiber implanted nearby, similar to fibers used for optogenetic stimulation.

“We don’t expect that everybody doing optogenetics will use this for every experiment — it’s more something that you would do once in a while, to see whether a paradigm that you’re using is really producing the profile of light that you think it should be,” Jasanoff said. 

In addition to optogenetic applications, the sensor has the potential to monitor patients undergoing light-based therapies for cancer, such as photodynamic therapy. The MIT team is now working on developing similar probes that can detect light emitted by luciferases, a family of glowing proteins commonly used in biological experiments. This advancement could allow imaging of luciferases in deeper tissues, surpassing the limitations of current techniques restricted to superficial tissue or lab-grown cells, the report states.

Jasanoff also envisions expanding the sensor's capabilities beyond light detection, according to the report. He aims to design MRI probes that can detect stimuli other than light, such as neurochemicals or other molecules present in the brain.

The research was funded by the National Institutes of Health, the G. Harold and Leila Y. Mathers Foundation, the Friends of the McGovern Fellowship, the MIT Neurobiological Engineering Training Program, and a Marie Curie Individual Fellowship from the European Commission, MIT News reports.