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Seeing what the hell is going on inside of us is useful for many aspects of modern medicine. But how to do this without cutting and cutting barriers such as flesh and bone to observe intact living tissue, such as our brains, is a difficult thing to do.
Thick, incoherent structures such as bone will scatter light unpredictably, making it difficult to understand what’s going on behind them. And the deeper you wish to see, the more diffused light obscures the fine and fragile biological structure.
There are many options for researchers who wish to see living tissue doing their thing, using clever optical tricks to turn scattered photons moving at certain frequencies into an image. But risking tissue damage or operating only at shallow depths, they all have drawbacks.
A team of scientists has now found a way to create a clear image from the diffuse infrared light emitted by a laser, even after it has passed through a thick layer of bone.
“Our microscope allows us to investigate subtle internal structures deep in living tissues 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 previously succeeded in capturing images of neurons under a mouse’s skull, most attempts to obtain crystalline images from bony-enveloped animal heads require cutting openings through the skull.
Three-photon microscopy uses longer wavelengths and a special gel to help see beyond the bone, however this method can only penetrate so deep and combines the frequencies of light in a way that risks damaging delicate biological molecules .
By combining imaging techniques with the power of computational adaptive optics previously used to correct optical distortion in terrestrial astronomy, Yoon and colleagues were able to create the first high-resolution images of mouse neural networks from behind its skull. intact.
Before and after image processing using aberration correction algorithm. (Yoon et al, Nature Communications, 2020)
They call their new imaging technology laser scanning reflection matrix microscopy (LS-RMM). It is based on conventional laser scanning confocal microscopy, except that it detects the scattering of light not only at the depth to be imaged, but also achieves a complete input-output response of the light-medium interaction – its reflection matrix.
When light (in this case, from a laser) passes through an object, some photons travel directly, while others are deflected. Bone, with its complex internal structure, is particularly good at scattering light.
The farther the light has to travel, the more those ballistic photons scatter out of the image. Most microscopy techniques rely on those light waves that shoot straight up to build a clear, bright image. LS-RRM uses a special matrix to get the most out of any aberrant light rays.
After recording the reflection matrix, the team used adaptive optics programming to pinpoint which light particles define and which dark ones. Together 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 the mouse neural networks from the data.
“The identification of wavefront aberrations relies on the inherent contrast of the reflectance of the targets,” the team explained in their paper. “As such, it requires no fluorescent labeling and high excitation power.”
Viewing biological structures in their natural life context has the potential to reveal more about their roles and functions, as well as allow for easier identification of problems.
“This will help us a lot in early detection of the disease and accelerate neuroscientific research,” said Yoon and Lee.
LS-RMM is limited by computing power, as it requires intensive and time-consuming computations to process complicated aberrations from small detailed areas. But the team suggests that their aberration correction algorithm could be applied to other imaging techniques as well to allow them to resolve even deeper images.
We can’t wait to see what this new technology will reveal hidden within us.
This research was published in Nature Communications.
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