Biomedical optics express最新文献

The Sagnac interferometer offers distinct advantages in vibrational wave detection. In this study, an air-coupled transducer and a compact fiber-optic Sagnac interferometer were developed for non-contact elasticity characterization in biological tissues. Given the challenge of limited light collection by a compact fiber optic Sagnac interferometer in biological tissues, this study aims to explore the potential of using a compact Sagnac interferometer to measure vibrational waves in biological tissues. The speeds of the generated vibrational surface waves in tissue-mimic phantoms were measured. Measurement errors caused by cross-correlation wave tracking were analyzed, and the performance of the integrated system was characterized. The results demonstrated the effectiveness of the integrated system and the cross-correlation algorithm in tracing the speed of vibrational surface waves in tissue-mimicking phantoms. They suggested potential applications for the non-invasive, contactless characterization of the mechanical properties in soft biological tissues.

Optical coherence tomography (OCT) is an interferometric technique for micron-level imaging in biological and non-biological contexts. As a non-invasive, non-ionizing, and video-rate imaging modality, OCT is widely used in biomedical and clinical applications, especially ophthalmology, where it functions in many roles, including tissue mapping, disease diagnosis, and intrasurgical visualization. In recent years, the rapid growth of medical robotics has led to new applications for OCT, primarily for 3D free-space scanning, volumetric perception, and novel optical designs for specialized medical applications. This review paper surveys these recent developments at the intersection of OCT and robotics and organizes them by degree of integration and application, with a focus on biomedical and clinical topics. We conclude with perspectives on how these recent innovations may lead to further advances in imaging and medical technology.

In vivo access to molecular information of retinal tissue is considered to play a critical role in enabling early diagnosis of ophthalmic and neurodegenerative diseases. The current gold standard of retina imaging, optical coherence tomography and angiography provides only the retinal morphology and blood perfusion, missing the full spectrum of molecular information. Raman spectroscopy addresses this gap while keeping the investigation non-invasive and label-free. Although previous studies have demonstrated the huge diagnostic potential of combining both modalities for in vivo biological tissue measurement, some have either employed unsafe optical power levels for in vivo retinal measurements or presented results that were negative or contradictory. In this study, we have developed an eye-safe multimodal in vivo label-free imaging system and demonstrate the potential of this device by investigating the retina of a living albino rat. The acquired Raman spectra showed relevant Raman bands in comparison with the previous ex vivo studies. Using this multimodal imaging system for non-invasive retina measurements of transgenic rodents holds the potential to advance the understanding of the pathophysiology of both ophthalmic and neurodegenerative diseases.

Immunofluorescence (IF) is a crucial technique in histopathology, enabling the visualization of multiple antibody distributions within single tissue specimens. However, autofluorescence (AF), which originates from endogenous molecules in formalin-fixed paraffin-embedded (FFPE) tissue, poses a persistent challenge by interfering with the fluorescence signal of interest in IF analysis. While photo-irradiative bleaching has emerged as a protocol to suppress the AF signal, there have been minimal quantitative investigations into this method across various experimental conditions. In this study, we investigated the efficacy of a bleaching-based method for reducing AF in FFPE human tissues. This research analyzed AF intensity as a function of exposure time, deparaffinization, emission range, and tissue types. Furthermore, by employing fluorescence lifetime imaging microscopy, we isolated the IF signal from AF to facilitate accurate quantification. This study provides valuable insights into AF reduction methodology to improve the reliability of IF-based histopathological analyses and advance our understanding of tissue biology and pathology.

Phacoemulsification with intraocular lens (IOL) implantation is a widely used effective treatment for cataracts. However, the surgical outcome relies heavily on precise operations with marked eye location and orientation, which ideally require a high-precision navigation system for complete guidance of surgical procedure. However, both research and current commercial surgical microscopes still face substantial challenges in handling various complex clinical scenarios. Here we propose a neural network-powered surgical microscopic system that can benefit from big data to address the unmet clinical need. In this system, we designed an end-to-end navigation network for real-time positioning and alignment of IOL and then built a computer-assisted surgical microscope with a complete imaging and display platform integrating the control software and algorithms for surgical planning and navigation. The network used an attention-based encoder-decoder architecture with an edge padding mechanism and an MLP layer for eye center localization, and combined siamese network, correlation filter, and spatial transformation network to track eye rotation. Using computer-aided annotation, we collected and labeled 100 clinical surgery videos from 100 patients, and proposed a data augmentation method to enhance the diversity of training. We further evaluated the navigation performance of the microscopic system on a human eye model.

This paper presents a non-contact and cost-effective method to assess venous hemodynamics along the lower limbs using photoplethysmography imaging (PPGI). Seventeen healthy volunteers performed the venous muscle pump test, inducing venous blood volume changes in their lower legs, which were recorded using a webcam. PPGI signals were extracted from three regions along the lower leg. Key parameters derived from a physiological model were evaluated and analyzed statistically: perfusion amplitude, ejection time constant, and peripheral venous flow index. The method demonstrated robust estimation of physiologically explainable parameters, and the potential to improve venous function diagnostics with high spatial resolution.

Methods for seeing inside volumetric images are increasingly important with the rapid advancements in 3D and 4D (3D + time) biomedical imaging techniques. Here, we report a novel volume clipping method and its open-source implementation which enables unprecedented 4D visualization and analysis of embryonic mouse heart development with data from optical coherence tomography (OCT). Clipping a volume to extract information inside has long been a vital approach in biomedical image analysis; however, it is challenging to make a dynamic non-planar cutaway view that is simultaneously smooth, adjustable, efficient to compute, easy to control, and interactive in real time. We addressed this challenge by applying the thin plate spline (TPS) to create a new way of volume clipping, called the clipping spline. Specifically, the clipping spline produces a cutaway view by generating a binary mask based on the unique TPS surface that intersects with a set of 3D control points while having minimal curvature. We implemented this method in an open-source platform where the clipping spline can be interactively controlled for real-time, adjustable, and dynamic cutaway views into a volume. We also developed an algorithm that automatically connects and interpolates different sets of control points over time, providing 4D volume clipping. In addition to characterizing the clipping spline, we demonstrate its application by revealing a series of never-before-seen dynamics and processes of embryonic mouse heart development based on OCT data. We also show a TPS-based method for tracking the embryonic myocardium with control points over two timescales (heartbeat and development). Our results indicate that the clipping spline promises to be broadly used in volumetric biomedical image visualization and analysis, especially by the OCT community.

Cells and other microscopic phase objects can be visualized in the living retina, non-invasively, using non-confocal light detection schemes in adaptive optics scanning light ophthalmoscopes (AOSLOs). There is not yet widespread agreement regarding the origin of image contrast, nor the best way to render multichannel images. Here, we present data to support the interpretation that variations in the intensity of non-confocal images approximate a direct linear mapping of the prismatic deflection of the scanned beam. We advance a simple geometric framework in which local 2D image gradients are used to estimate the spherocylindrical refractive power for each element of the tissue. This framework combines all available information from the non-confocal image channels simultaneously, reducing noise and directional bias. We show that image derivatives can be computed with a scalable, separable gradient operator that minimizes directional errors; this further mitigates noise and directional bias as compared with previous filtering approaches. Strategies to render the output of split-detector gradient operations have been recently described for the visualization of immune cells, blood flow, and photoreceptors; our framework encompasses these methods as rendering astigmatic refractive power. In addition to astigmatic power, we advocate the use of the mean spherical equivalent power, which appears to minimize artifacts even for highly directional micro-structures such as immune cell processes. We highlight examples of positive, negative, and astigmatic power that match expectations according to the known refractive indices and geometries of the relevant structures (for example, a blood vessel filled with plasma acts as a negatively powered cylindrical lens). The examples highlight the benefits of the proposed scheme for the visualization of diverse phase objects including rod and cone inner segments, immune cells near the inner limiting membrane, flowing blood cells, the intravascular cell-free layer, and anatomical details of the vessel wall.

Femtosecond laser pulses are employed in the preparation of implant cavities during dental implant surgeries in the field of digital dentistry, specifically focusing on optimizing laser pulse parameters to enhance precision and control thermal injury. In this study, ex vivo experiments were conducted on sheep tibiae, where thermocouple sensors monitored the temperature variations during ablation. This approach aims to optimize the laser pulse parameters and control the temperature, ensuring smoother cavity margins and better preservation of the bone microarchitecture. Scanning electron microscopy (SEM) confirmed significant improvements in the quality of the implant cavities prepared using the femtosecond laser pulses.

Dementia affects a large proportion of the world's population. Approaches that allow for early disease detection and non-invasive monitoring of disease progression are desperately needed. Current approaches are centred on costly imaging technologies such as positron emission tomography and magnetic resonance imaging. We propose an alternative approach to assess neurodegeneration based on diffuse correlation spectroscopy (DCS), a remote and optical sensing technique. We employ this approach to assess neurodegeneration in mouse brains from healthy animals and those with prion disease. We find a statistically significant difference in the optical speckle decorrelation times between prion-diseased and healthy animals. We directly calibrated our DCS technique using hydrogel samples of varying Young's modulus, indicating that we can optically measure changes in the brain tissue stiffness in the order of 60 Pa (corresponding to a 1 s change in speckle decorrelation time). DCS holds promise for contact-free assessment of tissue stiffness alteration due to neurodegeneration, with a similar sensitivity to contact-based (e.g. nanoindentation) approaches.