Biomedical optics express最新文献

Dual-modal ultrasound (US) and photoacoustic (PA) imaging with linear-array transducers offers clinically relevant imaging depths and flexible access to anatomical sites, while enhancing optical contrast. By integrating anatomical detail from US with the molecular specificity of PA, this approach provides complementary information that supports more accurate and comprehensive diagnostics than either modality alone. Despite its promise, high-quality video-rate dual-modal imaging remains hindered by two longstanding challenges. Conventional linear-array transducers, optimized for US by suppressing grating and side lobes, inherently limit the wide field of view (FOV) and broad fractional bandwidth necessary for effective PA detection. In contrast, concave arrays extend the FOV for PA but introduce substantial grating artifacts in US imaging, compromising structural fidelity. To overcome these constraints, we engineered a unified linear-concave transducer (ULC-T) that enables synchronized video-rate (100 Hz) plane-wave US and multispectral PA imaging on a standard 128-channel acquisition platform. The ULC-T integrates linear and concave segments into a unified array architecture. A spatial correction algorithm compensates for segmentation misalignments, reducing fabrication constraints, while a customized transmit-receive scheme enhances imaging performance. Validated across phantom, small animal, and human studies, the system demonstrates high imaging speed and deep tissue penetration, offering a practical solution to persistent dual-modal integration challenges and showing strong potential for clinical translation.

An accurate distinction between brain tumors and tumorless brain tissue is crucial for effective surgical resection. Polarization-sensitive optical imaging exploits birefringence differences, offering contrast between the optically anisotropic white matter of the tumorless brain and the optically isotropic brain tumor tissue. However, crossing brain fiber bundles within tumorless brain tissue may also erase such optical anisotropy. We use a polarized Monte Carlo algorithm to model backscattered wide-field Mueller matrix images of the optical phantoms of the brain's white matter. We compare the impact of fiber bundle crossing and the presence of an optically isotropic subsurface tumor across varying depths to mimic brain tissue removal during neurosurgery. The simulation results demonstrate that the depolarization dependence on depth may serve as a decisive parameter to distinguish the tumor and fiber bundles crossing zones, as the values of linear retardance drop in both zones, whereas the depolarization values become smaller in the tumor zone.

A major goal in the management of skin melanoma is to optimize early detection of the disease. The current gold standard method for diagnosing skin cancer relies on pathologists' interpretation of dermoscopy images and on histologic analysis, but this approach has low accuracy for melanoma detection and is time-consuming. Though advanced optical imaging technologies can increase the detection accuracy for non-melanoma skin cancer, they are still unreliable for melanoma detection and are associated with high costs for the equipment and training. In this study, a low-cost wide-field transmission microscope powered by Mueller matrix formalism and decomposition methods is developed to image collagen birefringence in normal human skin, melanoma, and common types of skin cancer (basal cell carcinoma or BCC and squamous cell carcinoma or SCC). The results show that two-dimensional images of retardance can highlight clusters of collagen fibers in tumorous skin. In addition, analyzing orientation as a function of retardance is useful to differentiate normal skin from tumorous skin, while analyzing orientation as a function of depolarization is useful in categorizing types of skin cancer.

Human vision is considered limited to the visible range (∼400-700 nm), yet studies have shown that near-infrared light can elicit visual perception through a nonlinear process known as two-photon vision. This occurs when two infrared photons are absorbed simultaneously by photopigments in the photoreceptors, generating a response equivalent to that of a single visible photon. While this phenomenon has been investigated for monochromatic stimuli, its potential for color perception remains unexplored. Here, we present the first functional prototype of a two-photon infrared RGB display and demonstrate that polychromatic color perception can be achieved by using infrared light alone. We have demonstrated that color mixing in this spectral range follows additive principles similar to those of visible light, enabling the perception of a wide gamut of hues, including white. These findings open new avenues for leveraging this alternative visual mechanism in practical applications requiring precise color control, such as immersive display technologies.

In the laser ablation and thermal therapy technologies, tissue-mimicking phantoms (TMPs) play a crucial role, enabling both the preclinical testing and equipment calibration, without the use of biological tissues. Special attention is paid to the simultaneous replication of optical, thermal, and mechanical properties of target tissues in a single TMP. Sodium alginate forms a promising material platform for the TMP development due to the tunability of its physical properties, biocompatibility, and exceptional thermal stability. Indeed, as a polysaccharide derived from brown seaweed, sodium alginate forms hydrogels (through the ionic cross-linking) with controllable mechanical and optical properties, and tailored texture and structural integrity. In this paper, the alginate-based TMP loaded by CuSO₄, as an absorptive component, and ovalbumin, as a scattering component that also models the thermal coagulation of proteins, is judiciously designed to capture the key optical, thermal, and mechanical properties of tissues. To make its applications in studies of the laser coagulation and ablation of hepatocellular carcinoma (HCC) of the liver possible, a case example of such a TMP is considered, which models the liver tissues at the 1064 nm wavelength. The experimental studies involving exposure of TMP to laser radiation demonstrate that it offers controlled coagulation thresholds and enables visualization of the heat-induced tissue damage through the reversible or irreversible phase transitions. Our findings uncover the potential of the developed TMP in laser thermotherapy technologies.

Quantitative methods of evaluating the state of skin are highly beneficial for both diagnosis and treatment monitoring. The development of such methods relies on understanding how changes in skin properties affect the quantitative response. Effective modelling is often a crucial step in building this understanding. This work introduces a multi-layered model for simulating the in vivo terahertz response of skin, demonstrating how variations in skin properties may alter the measured signal. Furthermore, we hypothesise that the observed attenuation in the terahertz signal during an in vivo measurement is primarily a result of skin deformation and flattening under compression by the imaging window. Finally, we fit our model to measured data and extract optimised values for a skin deformation parameter.

Adaptive optics (AO) enables cellular-resolution retinal imaging by correcting ocular aberrations, but its widespread clinical adoption remains limited by the narrow field of view (FOV) imposed by the isoplanatic patch of the eye. In this study, we present a deformable mirror (DM)-based sensorless AO time-domain full-field OCT (FFOCT) system that overcomes these limitations by leveraging the inherent robustness of FFOCT to ocular aberrations under spatially incoherent illumination. Using both phantom eye simulations and in vivo experiments, we demonstrate that correction of only three to five Zernike modes (defocus, astigmatism, and coma) is sufficient to significantly enhance SNR and resolve fine retinal structures. This includes reliable visualization of cone photoreceptors as close as 0.3^∘ from the foveal center and depth-resolved imaging of inner retinal features such as nerve fiber bundles, vessel walls, capillaries, internal limiting membrane, macrophage-like cells, and Gunn's dots, across a $5^{\circ }\times 5^{\circ }$ FOV at 500 Hz. By simplifying AO implementation while achieving wide-field cellular resolution, this approach addresses key limitations of current AO ophthalmoscopes and offers a promising pathway toward a wider clinical deployment of high-resolution retinal imaging.

Understanding the depth of penetration of near-infrared (NIR) light in biological tissue is critical for enhancing clinical applications of near-infrared spectroscopy (NIRS). The current knowledge of NIRS penetration depth primarily stems from mathematical models, numerical simulations, and phantom studies, with a notable knowledge gap derived from real animal models. By sequentially obstructing light from traversing in a porcine kidney tissue model, we derived the depth distribution of NIR light experimentally and better characterized its dependence on the distance between the light source and photodetector. We collected four replicates of data from six different source-detector distances (SDSs) and found that both the maximum and mean depths of penetration of NIRS increase with the SDS. Linear relationships can be derived between the SDS and the maximum depth, and the square root of the SDS and the mean depth.

Spatially-resolved reflectance (SRR) techniques are essential for in vivo noninvasive optical characterization of biological tissue. Under the common assumption of a single-layer volume to approximate human skin tissue, the long-standing issue of µ_a -µ_s ^' cross-talk warrants a thorough investigation and description of its potentially detrimental effects on the accuracy of measured absorption and reduced scatter. Using a two-layer model built from ex vivo measured porcine optical properties, we use analytical solutions to the radiative transfer equation to obtain calculated reflectance curves, which are fitted with a single-layer model to determine effective optical properties. We demonstrate systematic errors in fitted optical coefficients that display clear dependence on the optical properties of the two-layer medium and the inversion cost function. We provide a guide of the errors that a researcher may expect when performing in vivo optical characterization of biological tissue with SRR methods under the single-layer inverse model.

Existing optical phantoms often do not represent realistic optical and geometrical properties. This study aimed to fabricate a homogeneous silicone finger phantom that closely mimics the reflectance and transmittance characteristics of a human finger by precisely adjusting the absorption and reduced scattering coefficients in the visible wavelength range. The absorption and reduced scattering coefficients of a human finger were determined using a custom inverse model tailored for an integrating sphere system designed for cylindrical media illuminated along the barrel. To reproduce the retrieved optical properties in silicone, a reference database was created by characterizing the absorption spectra of 15 pigments dispersed in a silicone matrix. An automated fitting algorithm identified five suitable absorbing pigments, and their required concentrations were calculated to match the target absorption spectrum. The reduced scattering coefficient was independently controlled by varying the concentration of zirconium dioxide particles. An alginate mould was used to capture the finger geometry, ensuring anatomical accuracy of the phantom. The fabricated silicone finger phantom closely matched the human finger in both transmittance and reflectance, as well as in its anatomical shape. The ΔE ₂₀₀₀ value between the reflectance spectra of the human and silicone fingers was found to be 0.85. Under transmittance-mode illumination, light propagation within the silicone phantom agreed well with that of a human finger, both in visual appearance and in spatial light distribution. A method was developed to fabricate silicone finger phantoms with accurately matched optical and anatomical properties.