One step closer to early disease diagnosis
A high-resolution adaptive optical image that can eliminate biological tissue-induced image distortion developed
findings published in nature communications

▲ Research Team

Advancing early disease diagnosis requires a high-resolution adaptive optical imaging that can capture individual biological tissue. However, multiple light scattering and distorted images pose a risk of sharply lowering such resolution when targeting cells deep inside. As a result, imaging techniques currently available only allows us to observe cells on the surface properly. 

The research team led by Prof. Wonshik Choi, Vice Chief of the Center for IBS Molecular Spectroscopy and Dynamics, from Korea University developed collective accumulation of single-scattering (CASS) microscopy in order to effectively reduce multiple light scattering and take images of an object deep inside tissue. The Center (Chief: KU Prof. Minhaeng Cho) is affiliated with the Institute of Basic Science (President: Doochul Kim) under the Korean Ministry of Science and ICT. In this research, the research team developed a new method to correct not only multiple light scattering, but also specimen-induced aberrations. The method called the closed-loop accumulation of single scattering (CLASS) imaging performed a closed-loop optimization of signal waves in order to find the aberrations of single scattering, and as a result, a resolution twice the level from existing CASS microscope was acquired.

The specimen-induced aberrations create different depths of light by propagating angles of single scattering waves, thus distorting images and lowering brightness of the images. The same goes for objects behind thick glass. In fact, biological cells show far greater aberrations. For high-resolution imaging, such aberrations are hard to correct as aberrations of waves incident to and reflected from an object occur separately.

In order to eliminate aberrations, the research team adjusted the incidence angle of light and acquired light images reflected from the biological tissues. After acquiring a time-resolved reflection matrix, the angle-dependent aberration correction was performed in order to optimize the total intensity of the momentum. Furthermore, a phase-conjugation reflection matrix was acquired to consider the reversal process and an angle-dependent aberration correction was also performed. After rounds of iteration, angle-dependent aberrations for the forward and phase-conjugation processes were independently identified.

The research team achieved a spatial resolution of 600 nm up to an imaging for a resolution target under a 700 μm-thick tissue layer. For example, working with the research teams led by Ki Hean Kim from Pohang University of Science and Technology (POSTECH) and by Myoung Joon Kim from Asan Medical Center, they performed a high-resolution imaging of the fine multicellular filaments of fungal cells in rabbit cornea. CLASS imaging promises diverse bio applications, as it can be adapted to other widely used imaging technologies such as confocal microscopy and two-photon microscopy, and can also be embedded in endoscopes.

Prof. Choi, the corresponding author of the research, said, “This research is significant as it resolved the issue of distorted images by biological tissues that we should address in order to use optimal microscope in early disease diagnosis.”

 
The research findings were published in Nature Communications (IF 12.124) on December 18.

[ Figure Description ]

Figure 1: For the forward process (a), the time-resolved reflection matrix was acquired (b) for each incident angle. A Phase map was developed (c) for each angle that maximized the total intensity of reconstructed image, and then the phase correction was applied to reconstruct the image (d). For the phase-conjugation process (e), in which the phase correction is applied to the reversal process, the phase-conjugated reflection matrix (f) and the phase map (g) were acquired. The reconstructed image, after applying for the phase correction, is displayed in (h). After findings of iterations, maps for the illumination and imaging paths were acquired as illustrated in (i) and (j). The map was decomposed to 50 Zernike polynomials. The reconstructed image after correcting the aberrations was acquired (l) which confirmed the undistorted structure of the samples.

Figure 2: This is the image of a rabbit’s cornea (a) infected by A. fumigatus using CLASS microscopy. The fungus has a thin and long structure (b), and it was not clearly imaged due to due to the aberrations of the cornea (c). Using CLASS microscopy, data of aberrations were acquired (e) and a clear image of the fungi was confirmed after the correction of the aberrations (d).