Biomedical optics express最新文献

Pulsed IR light can be perceived as visible through a non-linear two-photon (2P) absorption process. Similar to visible light, the Stiles-Crawford effect of the first kind (SCE-I) predicts that the perceived brightness in 2P vision depends on the location of the incoming beam in the pupil. This study compared the SC effect intensity for both visible and IR light. The average (±1 SD) characteristic directionality parameter obtained from 11 participants was 0.080 ± 0.049 mm^-2 for the IR light and 0.059 ± 0.016 mm^-2 for the visible light. The mean difference was 0.021 ± 0.039 mm^-2 (95% CI: [-0.005, 0.047]) with a p-value of 0.11, suggesting similar photoreceptor directionality responses to both conventional one-photon and 2P excitation.

Nonlinear femtosecond (fs) laser ablation enables highly localized energy deposition for cell microsurgery. Conventional systems operate at either low (∼1 kHz, amplified µJ pulse energy) or high (∼80 MHz, unamplified low nJ) repetition rates, but intermediate rates with amplified pulse energy offer a promising balance of ablation speed and thermal control. We custom-built a low-cost, 32 MHz femtosecond fiber laser system with gain-managed nonlinear amplification, boosting pulse energy from 5 to 90 nJ while compressing pulse duration to 46 fs. In this intermediate-repetition-rate regime, the use of sub-50-fs pulses enhances ablation efficiency by strengthening multiphoton absorption and lowering the effective ablation threshold, while also leveraging multi-pulse incubation effects that promote cumulative energy deposition at reduced per-pulse energies. Compared to 200-500 fs pulses typically used for ablation, shorter durations double ablation efficiency in silicon and yield a ∼10× increase in cell membrane damage. In 3D tumor models, this approach enables targeted subsurface ablation up to 400 µm depth with 6 nJ pulse energy. These results inform the design of next-generation femtosecond laser systems for microsurgery.

Second-harmonic generation (SHG) microscopy enabled label-free, high-resolution visualization of ocular collagen structures in mouse, rabbit, and human pterygium tissues. Quantitative analyses using fast Fourier transform (FFT), gray-level co-occurrence matrix (GLCM), and polarization-resolved SHG revealed regional variations in collagen alignment, texture anisotropy, and optical polarization dependence. The results demonstrate that SHG imaging can sensitively capture microstructural organization and pathological remodeling within corneal and conjunctival tissues. This study highlights the potential of SHG microscopy as a powerful noninvasive technique for quantitative assessment of collagen integrity and early detection of structural abnormalities in ocular diseases.

In multiline-illumination Raman microscopy, background signals from the out-of-focus planes limit the throughput of cell imaging. Here, we improved the throughput of cell imaging by reducing background signals originating from the sample buffer solution and immersion medium of the objective lens. The background from water was suppressed by restricting the thickness of the sample buffer layer. In addition, the background signal in the CH stretching region was suppressed by replacing H₂O with D₂O as the immersion medium. These approaches successfully decreased background signals by 75%, enabling the same signal-to-noise ratio with a 2.2-fold shorter exposure time in cell imaging. Finally, we demonstrated high-throughput Raman imaging by visualizing bead uptake in living macrophages, successfully capturing 80 cells per frame within 3 min.

Fluorescence microscopy is an important imaging technique for biological research and applications. However, owing to various constraints in its engineering implementation and image acquisition, the acquired images often suffer from substantial noise. Although many denoising methods have been proposed, their applicability is limited by the distinct properties of fluorescence microscopy images. In particular, in real-world applications, it is often challenging and sometimes infeasible to acquire a large number of paired noisy-clean images for supervised training, and it is impractical to parameterize and estimate all types of real-world noise distributions. We propose ED-Diff, a zero-shot denoising algorithm based on diffusion priors. ED-Diff integrates the optimization solution of inverse problems with the diffusion sampling process and introduces a noisy image transformation module (NiTM) with an encoder-decoder structure to handle real-world noise scenarios. Extensive experiments on multiple real-world datasets validated the effectiveness of NiTM, demonstrating that ED-Diff exhibits competitive and robust performance.

Topically applied drug products are used to treat various dermatological conditions, enabling local and targeted delivery of active pharmaceutical ingredients. To ensure appropriate topical drug efficacy and delivery, it is necessary to understand the pharmacokinetics of topical drug uptake. Stimulated Raman scattering (SRS) microscopy, a chemically specific imaging modality, is well-suited to quantitatively measure the spatiotemporal kinetics of topical drug permeation in skin. However, SRS imaging depth in skin is often limited due to skin heterogeneity and scattering effects, distorting the laser focus and reducing the SRS signal. Adaptive optics (AO) can help overcome and correct depth limitations by adjusting wavefront shape and improving laser focus with a programmable optical element, such as a deformable membrane mirror. Previous work has demonstrated the use of AO in optimizing coherent anti-Stokes Raman scattering (CARS) signal in tissue imaging. In this study, we evaluated the ability of AO to improve the SRS signal in tissue imaging using a deformable membrane mirror as the AO element, which utilized a simulated annealing algorithm to search for mirror shapes producing optimal SRS signal at different tissue imaging depths. AO SRS images had an 11% increase in SRS signal intensity and >350% increase in image contrast between high and low signal regions compared to non-AO SRS images in nude mouse ear skin at the same depth. Mirror shapes optimized at greater imaging depths produced increased SRS intensity and contrast for a range of imaging depths (up to 290 μm in chicken muscle). Using AO SRS, we performed time-lapse imaging of ruxolitinib uptake in ex vivo human skin, demonstrating that AO SRS can be used to quantitatively measure topical drug pharmacokinetics in deeper skin structures (>100 μm).

The attenuation coefficient of biological tissue could serve as an indicator of structural and functional changes related to the onset or progression of disease. Optical coherence tomography (OCT) provides cross-sectional images of tissue up to a depth of a few millimeters, based on the local backscatter properties. Monte Carlo (MC) simulations are ideally suited to investigate and improve OCT attenuation coefficient extraction in confounding cases of (low-order) multiple scattering and inclusions such as blood vessels. However, current MC methods are time-consuming due to the OCT detection configuration rejecting many of the backscattered photons. In this work, we present two MC OCT detection models, a conventional photon detection model and a hybrid particle-wave detection model based on spherical waves from a photon's last scatter position, and compare their simulation efficiency by comparing the SNR of the resulting depth profiles for equal conditions and number of simulated photons. We find a three orders of magnitude increase in the simulation efficiency for the hybrid particle-wave model compared to the conventional photon detection model. Both models show excellent agreement with single-scatter theory for weakly scattering samples. Additionally, we use the hybrid particle-wave model to simulate experimentally measured samples with 0.1 mm^-1 ≤µ _s  ≤ ~4.5 mm^-1. The resulting simulated depth profiles show excellent agreement with the experimental depth profiles, even in those cases where the single-scatter theory model fails to describe the experimental depth profiles accurately.

Our previous studies demonstrated that a prototype photoacoustic (PA) and ultrasound (US) imaging catheter can differentiate intestinal inflammation and fibrosis. However, its compatibility with clinical endoscopic procedures has not been validated. Here, we present a translational PA-US dual-modality imaging catheter with a reduced diameter to fit the biopsy channel of standard adult colonoscopes and therapeutic upper endoscopes (∼3.7 mm). The catheter integrates an angle-tipped optical fiber (600-µm core) for PA illumination and a miniaturized 48-element ultrasound array operating at a center frequency of ∼9 MHz for signal reception. These components are enclosed in a hydrostatic balloon (12 mm diameter, 15 mm length when fully inflated) to ensure acoustic coupling with the intestinal lumen. The system was upgraded from our previous setup by incorporating a more portable optical parametric oscillator (OPO) laser and a Verasonics imaging platform. The imaging catheter was positioned at the disease locations in a pig model of esophageal fibrosis induced by argon plasma coagulation (APC). Multi-wavelength PA imaging and US imaging were performed to resolve the tissue components. The results demonstrate the catheter's ability to assess inflammation and fibrosis in the gastrointestinal tract during a standard clinical endoscopy procedure.

Kidney transplantation remains the preferred treatment for patients with end-stage kidney disease. However, the ongoing shortage of donor organs continues to limit the availability of transplant treatments. Existing evaluation methods, such as the kidney donor profile index (KDPI) and pre-transplant donor biopsy (PTDB), have various limitations, including low discriminative power, invasiveness, and sampling errors, which reduce their effectiveness in organ quality assessment and contribute to the risk of unnecessary organ discard. In this study, we explored the dynamic optical coherence tomography (DOCT) as a label-free, non-invasive approach to monitor the viability of ex vivo mouse kidneys during static cold storage over 48 hours. The dynamic metrics logarithmic intensity variance (LIV), early OCT correlation decay speed (OCDS _e ), and late OCT correlation decay speed (OCDS _l ) were extracted from OCT signal fluctuations to quantify temporal and spatial tissue activity and deterioration. Our results demonstrate that DOCT provides complementary information relevant to tissue viability, in addition to the morphological assessment offered by conventional OCT imaging, showing potential to improve pre-transplant organ evaluation and clinic decision-making.

The transport of intensity equation (TIE) is a powerful phase imaging technique. However, its formulation fails to account for the off-axial transfer function due to the paraxial approximation. To address the resulting image degradation, we analyze TIE phase retrieval using the contrast transfer function (CTF) framework. The attenuation of high-frequency components, leading to the loss of fine structural details, is assessed and restored through Wiener deconvolution. Simulations and experiment results demonstrate significant enhancements in sharpness, contrast, and structural clarity. We showcase enhanced phase imaging of cheek cells, revealing finer subcellular details and achieving diffraction-limited performance, contributing to advances in super-resolution phase imaging.