Biomedical optics express最新文献

Detecting subtle alterations in cardiac pulse transmission through the cerebral microvascular network could provide a new avenue for characterising cerebral microvascular health and aid in the research and diagnosis of related neurological pathologies. We used laser speckle contrast imaging to quantify the pulse waveform in cerebral microvasculature in awake and anaesthetised mice. Pulse amplitude was attenuated more efficiently in awake mice, with venular pulsatility index 63% lower than arterial, compared to a 9% and 30% reduction under isoflurane and ketamine-xylazine, respectively. Arterial-to-venous delay was similar when awake and under isoflurane (5.3±1.6 and 5.4±1 ms) but longer under ketamine-xylazine (10.3±1.7 ms).

Laser ablation offers the potential for precisely removing pathological tissue without damaging surrounding healthy structures. Among the existing laser types, deep ultraviolet ultrashort pulsed lasers offer the highest axial precision and reduced collateral damage, yet their application for ablating soft tissues apart from the cornea remains underexplored. Here, ablation of ex vivo lamb liver using laser pulses at 206 nm wavelength and 250 fs pulse duration is investigated. Laser parameters that enable clean, controlled tissue removal are identified by systematically varying the laser pulse energy, spot size, and pulse repetition rate, and the ablated tissues are analysed using histological analysis and surface profilometry. With optimised settings, tissue removal with axial precision down to 10 microns is demonstrated. Ablation threshold fluence of 38.7 ± 2.1 mJ·cm^-2 is determined for lamb liver tissue, and fluence windows yielding precise ablation with no observable collateral damage are defined for different laser spot sizes. The ablation responses of tissues with different physical properties are also investigated. These results advance understanding of laser-tissue interaction in the deep ultraviolet ultrashort pulse regime and demonstrate the potential of the proposed tissue removal method for high-precision surgical applications.

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).

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.

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.