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Seeing what is going on inside of us is useful for many aspects of modern medicine. But how to do this without slicing and dicing through barriers like flesh and bones to observe intact living tissue, like our brains, is a tricky thing to do.
Thick, inconsistent structures like bone scatter light in unpredictable ways, making it difficult to understand what is going on behind them. And the deeper you want to see, the more the scattered light obscures the fine and fragile biological structure.
There are plenty of options for researchers keen to watch living tissue do their job, using clever optical tricks to transform scattered photons traveling at certain frequencies into an image. But by risking tissue damage or only operating at shallow depths, they all have drawbacks.
A team of scientists have now found a way to create a clear image from the scattered infrared light emitted by a laser, even after passing through a thick layer of bone.
“Our microscope allows us to study fine internal structures deep within living tissue that cannot be resolved by any other means,” said physicists Seokchan Yoon and Hojun Lee of Korea University.
While a technique called three-photon microscopy has been successful in capturing images of neurons under a mouse skull before, most attempts to obtain crystal-clear images from the heads of bony-enveloped animals require cutting openings. through the skull.
Three-photon microscopy uses longer wavelengths and a special gel to help see beyond the bone, but this method can only penetrate so deeply and combines the light frequencies in a way that risks dying. ‘damage delicate biological molecules.
By combining imaging techniques with the power of computational adaptive optics previously used to correct optical distortion in ground-based astronomy, Yoon and his colleagues were able to create the first-ever high-resolution images of mouse neural networks behind his intact skull. .
Image processing before and after by aberration correction algorithm. (Yoon et al, Nature communications, 2020)
They call their new imaging technology laser reflection matrix microscopy (LS-RMM). It is based on conventional laser scanning confocal microscopy, except that it detects light scattering not only at the depth at which the image is photographed, but also obtains a full I / O response from the interaction. light-medium – its reflection matrix.
When light (in this case, from a laser) passes through an object, some photons pass directly through, while others are deflected. Bone, with its complex internal structure, is particularly effective in diffusing light.
The farther the light has to travel, the more these ballistic photons are scattered outside the image. Most microscopy techniques rely on these straight light waves to create a clear, bright image. LS-RRM uses a special matrix to make the most of all aberrant light rays.
After recording the reflection matrix, the team used adaptive optics programming to sort out which particles of light define and which obscure. With a spatial light modulator to help correct other physical aberrations that occur at such small imaging scales, they were able to generate an image of mouse neural networks from the data.
“The identification of wavefront aberrations is based on the intrinsic reflectance contrast of the targets,” the team explained in their paper. “As such, it does not require fluorescent labeling and high excitation power.”
Visualizing biological structures in their natural living context has the potential to reveal more about their roles and functions and to allow easier detection of problems.
“This will help us greatly in the early diagnosis of the disease and will speed up research in neuroscience,” said Yoon and Lee.
The LS-RMM is limited in computing power, as it requires intense and time-consuming calculations to process complex aberrations from small, detailed areas. But the team suggests that their aberration correction algorithm could also be applied to other imaging techniques to allow them to resolve deeper images as well.
We can’t wait to see what this new technology will reveal hidden within us.
This research was published in Nature’s communications.
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