Computational conjugate adaptive optics microscopy for longitudinal through-skull imaging of cortical myelin
Yongwoo Kwon, Jin Hee Hong, Sungsam Kang, Hojun Lee, Yonghyeon Jo, Ki Hean Kim, Seokchan Yoon, Wonshik Choi
IF 15.7
Nature Communications
Myelination processes are closely related to higher brain functions such as learning and memory. While their longitudinal observation has been crucial to understanding myelin-related physiology and various brain disorders, skull opening or thinning has been required to secure clear optical access. Here we present a high-speed reflection matrix microscope using a light source with a wavelength of 1.3 μm to reduce tissue scattering and aberration. Furthermore, we develop a computational conjugate adaptive optics algorithm designed for the recorded reflection matrix to optimally compensate for the skull aberrations. These developments allow us to realize label-free longitudinal imaging of cortical myelin through an intact mouse skull. The myelination processes of the same mice were observed from 3 to 10 postnatal weeks to the depth of cortical layer 4 with a spatial resolution of 0.79 μm. Our system will expedite the investigations on the role of myelination in learning, memory, and brain disorders.
Tracing multiple scattering trajectories for deep optical imaging in scattering media
Sungsam Kang, Yongwoo Kwon, Ho‐Jun Lee, Se‐Ho Kim, Jin Hee Hong, Seokchan Yoon, Wonshik Choi
IF 15.7
Nature Communications
Multiple light scattering hampers imaging objects in complex scattering media. Approaches used in real practices mainly aim to filter out multiple scattering obscuring the ballistic waves that travel straight through the scattering medium. Here, we propose a method that makes the deterministic use of multiple scattering for microscopic imaging of an object embedded deep within scattering media. The proposed method finds a stack of multiple complex phase plates that generate similar light trajectories as the original scattering medium. By implementing the inverse scattering using the identified phase plates, our method rectifies multiple scattering and amplifies ballistic waves by almost 600 times. This leads to a significant increase in imaging depth-more than three times the scattering mean free path-as well as the correction of image distortions. Our study marks an important milestone in solving the long-standing high-order inverse scattering problems.
Deep-tissue optical imaging suffers from the reduction of resolving power due to tissue-induced optical aberrations and multiple scattering noise. Reflection matrix approaches recording the maps of backscattered waves for all the possible orthogonal input channels have provided formidable solutions for removing severe aberrations and recovering the ideal diffraction-limited spatial resolution without relying on fluorescence labeling and guide stars. However, measuring the full input-output response of the tissue specimen is time-consuming, making the real-time image acquisition difficult. Here, we present the use of a time-reversal matrix, instead of the reflection matrix, for fast high-resolution volumetric imaging of a mouse brain. The time-reversal matrix reduces two-way problem to one-way problem, which effectively relieves the requirement for the coverage of input channels. Using a newly developed aberration correction algorithm designed for the time-reversal matrix, we demonstrated the correction of complex aberrations using as small as 2% of the complete basis while maintaining the image reconstruction fidelity comparable to the fully sampled reflection matrix. Due to nearly 100-fold reduction in the matrix recording time, we could achieve real-time aberration-correction imaging for a field of view of 40 × 40 µm<sup>2</sup> (176 × 176 pixels) at a frame rate of 80 Hz. Furthermore, we demonstrated high-throughput volumetric adaptive optical imaging of a mouse brain by recording a volume of 128 × 128 × 125 µm<sup>3</sup> (568 × 568 × 125 voxels) in 3.58 s, correcting tissue aberrations at each and every 1 µm depth section, and visualizing myelinated axons with a lateral resolution of 0.45 µm and an axial resolution of 2 µm.
A mouse skull is a barrier for high-resolution optical imaging because its thick and inhomogeneous internal structures induce complex aberrations varying drastically from position to position. Invasive procedures creating either thinned-skull or open-skull windows are often required for the microscopic imaging of brain tissues underneath. Here, we propose a label-free imaging modality termed laser scanning reflection-matrix microscopy for recording the amplitude and phase maps of reflected waves at non-confocal points as well as confocal points. The proposed method enables us to find and computationally correct up to 10,000 angular modes of aberrations varying at every 10 × 10 µm<sup>2</sup> patch in the sample plane. We realized reflectance imaging of myelinated axons in vivo underneath an intact mouse skull, with an ideal diffraction-limited spatial resolution of 450 nm. Furthermore, we demonstrated through-skull two-photon fluorescence imaging of neuronal dendrites and their spines by physically correcting the aberrations identified from the reflection matrix.
Computational conjugate adaptive optics microscopy for longitudinal through-skull imaging of cortical myelin
Yongwoo Kwon, Jin Hee Hong, Sungsam Kang, Hojun Lee, Yonghyeon Jo, Ki Hean Kim, Seokchan Yoon, Wonshik Choi
IF 15.7
Nature Communications
Myelination processes are closely related to higher brain functions such as learning and memory. While their longitudinal observation has been crucial to understanding myelin-related physiology and various brain disorders, skull opening or thinning has been required to secure clear optical access. Here we present a high-speed reflection matrix microscope using a light source with a wavelength of 1.3 μm to reduce tissue scattering and aberration. Furthermore, we develop a computational conjugate adaptive optics algorithm designed for the recorded reflection matrix to optimally compensate for the skull aberrations. These developments allow us to realize label-free longitudinal imaging of cortical myelin through an intact mouse skull. The myelination processes of the same mice were observed from 3 to 10 postnatal weeks to the depth of cortical layer 4 with a spatial resolution of 0.79 μm. Our system will expedite the investigations on the role of myelination in learning, memory, and brain disorders.
Tracing multiple scattering trajectories for deep optical imaging in scattering media
Sungsam Kang, Yongwoo Kwon, Ho‐Jun Lee, Se‐Ho Kim, Jin Hee Hong, Seokchan Yoon, Wonshik Choi
IF 15.7
Nature Communications
Multiple light scattering hampers imaging objects in complex scattering media. Approaches used in real practices mainly aim to filter out multiple scattering obscuring the ballistic waves that travel straight through the scattering medium. Here, we propose a method that makes the deterministic use of multiple scattering for microscopic imaging of an object embedded deep within scattering media. The proposed method finds a stack of multiple complex phase plates that generate similar light trajectories as the original scattering medium. By implementing the inverse scattering using the identified phase plates, our method rectifies multiple scattering and amplifies ballistic waves by almost 600 times. This leads to a significant increase in imaging depth-more than three times the scattering mean free path-as well as the correction of image distortions. Our study marks an important milestone in solving the long-standing high-order inverse scattering problems.
Deep-tissue optical imaging suffers from the reduction of resolving power due to tissue-induced optical aberrations and multiple scattering noise. Reflection matrix approaches recording the maps of backscattered waves for all the possible orthogonal input channels have provided formidable solutions for removing severe aberrations and recovering the ideal diffraction-limited spatial resolution without relying on fluorescence labeling and guide stars. However, measuring the full input-output response of the tissue specimen is time-consuming, making the real-time image acquisition difficult. Here, we present the use of a time-reversal matrix, instead of the reflection matrix, for fast high-resolution volumetric imaging of a mouse brain. The time-reversal matrix reduces two-way problem to one-way problem, which effectively relieves the requirement for the coverage of input channels. Using a newly developed aberration correction algorithm designed for the time-reversal matrix, we demonstrated the correction of complex aberrations using as small as 2% of the complete basis while maintaining the image reconstruction fidelity comparable to the fully sampled reflection matrix. Due to nearly 100-fold reduction in the matrix recording time, we could achieve real-time aberration-correction imaging for a field of view of 40 × 40 µm<sup>2</sup> (176 × 176 pixels) at a frame rate of 80 Hz. Furthermore, we demonstrated high-throughput volumetric adaptive optical imaging of a mouse brain by recording a volume of 128 × 128 × 125 µm<sup>3</sup> (568 × 568 × 125 voxels) in 3.58 s, correcting tissue aberrations at each and every 1 µm depth section, and visualizing myelinated axons with a lateral resolution of 0.45 µm and an axial resolution of 2 µm.
A mouse skull is a barrier for high-resolution optical imaging because its thick and inhomogeneous internal structures induce complex aberrations varying drastically from position to position. Invasive procedures creating either thinned-skull or open-skull windows are often required for the microscopic imaging of brain tissues underneath. Here, we propose a label-free imaging modality termed laser scanning reflection-matrix microscopy for recording the amplitude and phase maps of reflected waves at non-confocal points as well as confocal points. The proposed method enables us to find and computationally correct up to 10,000 angular modes of aberrations varying at every 10 × 10 µm<sup>2</sup> patch in the sample plane. We realized reflectance imaging of myelinated axons in vivo underneath an intact mouse skull, with an ideal diffraction-limited spatial resolution of 450 nm. Furthermore, we demonstrated through-skull two-photon fluorescence imaging of neuronal dendrites and their spines by physically correcting the aberrations identified from the reflection matrix.
High-resolution optical microscopy has transformed biological imaging, yet its resolution and contrast deteriorate with depth due to multiple light scattering. Conventional correction strategies typically approximate the medium as one or a few discrete layers. While effective in the presence of dominant scattering layers, these approaches break down in thick, volumetric tissues, where accurate modeling would require an impractically large number of layers. To address this challenge, we introduce an inverse-scattering framework that represents the entire volume as a superposition of angular deflectors, each corresponding to scattering at a specific angle. This angular formulation is particularly well suited to biological tissues, where narrow angular spread due to the dominant forward scattering allow most multiple scattering to be captured with relatively few components. Within this framework, we solve the inverse problem by progressively incorporating contributions from small to large deflection angles. Applied to simulations and in vivo reflection-mode imaging through intact mouse skull, our method reconstructs up to 121 angular components, converting ~80% of multiply scattered light into signal. This enables non-invasive visualization of osteocytes in the skull that remain inaccessible to existing layer-based methods. These results establish the scattering-angle basis as a deterministic framework for imaging through complex media, paving the way for high-resolution microscopy deep inside living tissues.
Implementation of reflection matrix microscopy: an algorithm perspective
Sungsam Kang, Seokchan Yoon, Wonshik Choi
IF 8.4
Journal of Physics Photonics
Abstract Over the past decade, reflection matrix microscopy (RMM) and advanced image reconstruction algorithms have emerged to address the fundamental imaging depth limitations of optical microscopy in thick biological tissues and complex media. In this study, we introduce significant advancements in reflection matrix processing algorithms, including logical indexing, power iterations, and low-frequency blocking. These enhance the processing speed of aperture synthesis, 3D image reconstruction, and aberration correction by orders of magnitude. Detailed algorithm implementations, along with experimental data, are provided to facilitate the widespread adoption of RMM in various deep-tissue imaging applications.
Device Design Guidelines to Boost Up AC Performance of CFET (Complementary Field-Effect-Transistor)-Based Inverter
Jaehyuk Lim, Donghwan Han, Juho Sung, Seokchan Yoon, Sanghyun Kang, Gwon Kim, Hyoung Won Baac, Changhwan Shin
IF 2.9
IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems
Complementary field-effect transistors (CFETs) have emerged as promising candidates for next-generation semiconductor devices. CFETs feature a structure with an nMOS (or pMOS) transistor at the bottom and a transistor of the opposite type at the top. CFETs can be classified into Fin-CFETs or GAA-CFETs based on their channel structure. In this study, we compare and analyze these two devices to determine which structure is more favorable for device scaling and which device exhibits better performance per unit area. For a reliable analysis, the threshold voltage was adjusted to be the same for all devices. Initially, to compare the DC performance, the on-state drive currents in both linear mode and saturation mode operations were extracted and compared from the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\mathrm { DS}}$ </tex-math></inline-formula>-versus-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm { GS}}$ </tex-math></inline-formula> input-transfer characteristics. Subsequently, complementary metal-oxide-semiconductor inverters were constructed to compare their AC performance. Six parameters were extracted and compared: high-to-low propagation delay (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{pLH}$ </tex-math></inline-formula>), falling time (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{f}$ </tex-math></inline-formula>), low-to-high propagation delay (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{pLH}$ </tex-math></inline-formula>), rising time (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{r}$ </tex-math></inline-formula>), overshoot voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{ov}$ </tex-math></inline-formula>), and undershoot voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{und}$ </tex-math></inline-formula>). Based on the results, we suggest which CFET structure is more suitable for device scaling.
