Compensation for sample-induced optical aberrations is crucial for visualizing microscopic structures deep within biological tissues. However, strong multiple scattering restricts the ability to detect and repair tissue-induced errors.
Therefore, to obtain a high-resolution deep tissue image, it is essential to eliminate multi-scatter waves and increase the proportion of single-scatter waves. The scientists, led by Associate Director CHOI Wonshik of the Center for Molecular Spectroscopy and Dynamics at the Institute of Basic Sciences, Professor KIM Moonseok of the Catholic University of Korea, and Professor CHOI Myunghwan of Seoul National University, developed a new type of holographic microscope to see through the skull and imagine the brain.
The new microscope can “see through” the intact skull and is capable of obtaining high-resolution 3D images of the neural network within a living mouse brain without removing the skull.
In 2019, scientists from IBS– for the first time – developed the high-speed time-resolved holographic microscope that can eliminate multiple scattering. At the same time, it measures the amplitude and phase of the light.
Using the microscope, they were able to observe the neural network of living fish without incisional surgery. However, it was difficult to image the neural network of the brains of mice, since a mouse’s skull is thicker than a fish’s.
The study team was able to quantitatively analyze how light and matter interact, allowing them to further develop their earlier microscope. This recent study reported the successful development of a super-depth three-dimensional time-resolved holographic microscope that enables observation of tissue deeper than ever before.
Specifically, the scientists developed a method to preferentially select single-scattering waves by taking advantage of the fact that they have similar reflection waveforms, even when light is received from various angles.
To discover the resonance mode that optimizes constructive interference (interference that occurs when waves of the same phase overlap), a complicated algorithm and numerical operation are used that examine the eigenmode of a medium (a different wave that distributes energy light in a medium). This allowed the new microscope to selectively filter out unwanted signals while focusing more than 80 times more light energy on brain fibers than before. This made it possible to increase the ratio of single-scatter waves to multi-scatter waves by several orders of magnitude.
The scientists then tested the technology by looking at the mouse brain. Even at a depth where it was previously impossible to use current technology, wavefront distortion could be corrected under the microscope. The new microscope obtained images of the neural network of the mouse brain below the skull in high resolution. All of this was accomplished at the visible wavelength without removing the mouse skull and without using a fluorescent marker.
Professor KIM Moonseok and Dr. JO Yonghyeon, who developed the basis of the holographic microscope, said: “When we first observed the optical resonance of complex media, our work received a great deal of attention from the academic world. From the basic principles to the practical application of observing the neural network under the mouse skull, we have blazed a new trail for convergent brain neuroimaging technology by combining the efforts of talented people in physics, life, and brain Sciences.”
Associate Director CHOI Wonshik said: “For a long time, our Center has developed deep bioimaging technology that applies physical principles. Our current finding is expected to greatly contribute to the development of interdisciplinary biomedical research, including neuroscience and the precision metrology industry.”
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