Compensation of sample-induced optical aberrations is crucial for visualizing microscopic structures deep within biological tissues. Strong multiple scattering, however, restricts the ability to detect and repair tissue-induced errors.
Therefore, to obtain a high-resolution deep-tissue image, removing the multiple-scattered waves and increasing the ratio of the single-scattered waves is essential. Scientists, led by Associate Director CHOI Wonshik of the Center for Molecular Spectroscopy and Dynamics within the Institute for Basic Science, 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 image the brain.
The new microscope can achieve “see through” the intact skull and is capable of high-resolution 3D imaging 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 light.
Using the microscope, they could observe the neural network of live fish without incisional surgery. However, it was difficult to obtain a neural network image of mice’s brain as a mouse’s skull is thicker than that of fish.
The study team was able to quantitatively analyze how light and matter interact, which allowed them to develop their earlier microscope further. This recent study reported the successful development of a super-depth, three-dimensional time-resolved holographic microscope that allows the observation of tissues to a greater depth than ever before.
Scientists, specifically, developed a method to preferentially select single-scattered waves by taking advantage of the fact that they have similar reflection waveforms even when light is input from various angles.
To discover the resonance mode that optimizes constructive interference (interference that happens when waves of the same phase overlap), a complicated algorithm and numerical operation examining the eigenmode of a medium (a distinct wave that distributes light energy into a medium) are used. This allowed the new microscope to selectively filter out unwanted signals while focusing more than 80 times as much light energy on the brain fibers as previously. This made it possible to increase the ratio of single-scattered waves to multiple-scattered waves by several orders of magnitude.
Scientists next tested the technology by observing the mouse brain. Even at a depth where employing current technology was previously impossible, the wavefront distortion could be corrected using the microscope. The new microscope successfully imaged the neuronal network of the mouse brain beneath the skull in high resolution. All of this was accomplished in the visible wavelength without taking the mouse’s skull out and without using a fluorescent marker.
Professor KIM Moonseok and Dr. JO Yonghyeon, who have developed the foundation of the holographic microscope, said, “When we first observed the optical resonance of complex media, our work received great attention from academia. From basic principles to practical application of observing the neural network beneath the mouse skull, we have opened a new way for brain neuroimaging convergent technology by combining the efforts of talented people in physics, life, and brain science.”
Associate Director CHOI Wonshik said, “For a long time, our Center has developed super-depth bioimaging technology that applies physical principles. It is expected that our present finding will greatly contribute to the development of biomedical interdisciplinary research, including neuroscience and the industry of precision metrology.”
- Yonghyeon Jo, Ye-Ryoung Lee, Jin Hee Hong, Dong-Young Kim, Junhwan Kwon, Myunghwan Choi, Moonseok Kim, Wonshik Choi. Through-skull brain imaging in vivo at visible wavelengths via dimensionality reduction adaptive-optical microscopy. Science Advances, 2022; 8 (30) DOI: 10.1126/sciadv.abo4366