Jin-Hee Hong | Searcharxiv

arXiv2024

Multiphoton super-resolution imaging via virtual structured illumination

Imaging in thick biological tissues is often degraded by sample-induced aberrations, which reduce image quality and resolution, particularly in super-resolution techniques. While hardware-based adaptive optics, which correct aberrations using wavefront shaping devices, provide an effective solution, their complexity and cost limit accessibility. Computational methods offer simpler alternatives but struggle with complex aberrations due to the incoherent nature of fluorescence. Here, we present a deep-tissue super-resolution imaging framework that addresses these challenges with minimal hardware modification. By replacing the photodetector in a standard laser-scanning microscope with a camera, we measure an incoherent response matrix (IRM). A dual deconvolution algorithm is developed to decompose the IRM into excitation and emission optical transfer functions and the object spectrum. The proposed method simultaneously corrects excitation and emission point-spread functions (PSFs), achieving a resolution of λ/4, comparable to structured illumination microscopy. Unlike existing computational methods that rely on vector decomposition of a single convoluted PSF, our matrix-based approach enhances image reconstruction, particularly for high spatial frequency components, enabling super-resolution even in the presence of complex aberrations. We validated this framework with two-photon super-resolution imaging, achieving a lateral resolution of 130 nanometers at a depth of 180 micrometers in thick mouse brain tissue.

physics.optics↗

arXiv2022

Acousto-optic volumetric gating for reflection-mode deep optical imaging within a scattering medium

The imaging depth of deep-tissue optical microscopy is governed by the performance of the gating operation that suppresses the multiply scattered waves obscuring the ballistic waves. Although various gating operations based on confocal, time-resolved/coherence-gated, and polarization-selective detections have proven to be effective, each has its own limitation; certain types of multiply scattered waves can bypass the gating. Here, we propose a method, volumetric gating, that introduces ultrasound focus to confocal reflectance imaging to suppress the multiply scattered waves traveling outside the ultrasonic focal volume. The volumetric gating axially rejects the multiply scattered wave traveling to a depth shallower than the object plane while suppressing the deeper penetrating portion that travels across the object plane outside the transversal extent of the ultrasonic focus of 30${\times}$90$ μm^2$. These joint gating actions along the axial and lateral directions attenuate the multiply scattered waves by a factor of 1/1000 or smaller, thereby extending the imaging depth to 12.1 times the scattering mean free path while maintaining the diffraction-limited resolution of 1.5 $μ$m. We demonstrated an increase in the imaging depth and contrast for internal tissue imaging of mouse colon and small intestine through their outer walls. We further developed theoretical and experimental frameworks to characterize the axial distribution of light trajectories inside scattering media. The volumetric gating will serve as an important addition to deep-tissue imaging modalities and a useful tool for studying wave propagation in scattering media.

physics.optics↗