Red blood cell (RBC) aggregation as well as their deformation significantly affects blood microrheology. These processes depend on various factors, one of which is concentration of the nitric oxide, one of the main signaling molecule in the bloodstream. The purpose of this study was to investigate the effect of nitric oxide on the microrheological properties of red blood cells (RBCs) in RBC samples of various media after the addition of nitric oxide donor sodium nitroprusside in vitro. Microrheological properties were measured using laser aggregometer and ektacytometer based on diffuse light scattering and diffraction of laser light on a suspension of RBCs, respectively. The study found that heparin-stabilized blood showed increased RBC aggregation and deformation with sodium nitroprusside concentrations of 100, and 200μM, while EDTA-stabilized blood showed slightly decreased aggregation and unchanged deformation. With washed RBCs in dextran solution, the addition of sodium nitroprusside (in the concentrations of 100, and 200μM) resulted in decreased aggregation and increased deformation. These findings aid in our understanding of nitric oxide’s effect on RBC microrheological properties.

A refined analytical model of spatially resolved diffuse reflectance with small source-detector separations (SDSs) for the in vivo skin studies is proposed. Compared to the conventional model developed by Farrell et al., it accounts for the limited acceptance angle of the detector fiber. The refined model is validated in the wide range of optical parameters by Monte Carlo simulations of skin diffuse reflectance at SDSs of units of mm. Cases of uniform dermis and two-layered epidermis-dermis structures are studied. Higher accuracy of the refined model compared to the conventional one is demonstrated in the separate, constraint-free reconstruction of absorption and reduced scattering spectra of uniform dermis from the Monte Carlo simulated data. In the case of epidermis-dermis geometry, the recovered values of reduced scattering in dermis are overestimated and the recovered values of absorption are underestimated for both analytical models. Presumably, in the presence of a thin mismatched topical layer, only the effective attenuation coefficient of the bottom layer can be accurately recovered using a diffusion theory-based analytical model while separate reconstruction of absorption and reduced scattering fails due to the inapplicability of the method of images. These findings require implementation of more sophisticated models of light transfer in inhomogeneous media in the recovery algorithms.

Monte Carlo simulation techniques have become the quintessence and a pivotal nexus of inquiry in the realm of simulating photon movement within biological fabrics. Through the stochastic sampling of tissue archetypes delineated by explicit optical characteristics, Monte Carlo simulations possess the theoretical capacity to render unparalleled accuracy in the depiction of exceedingly intricate phenomena. Nonetheless, the quintessential challenge associated with Monte Carlo simulation methodologies resides in their extended computational duration, which significantly impedes the refinement of their precision. Consequently, this discourse is specifically dedicated to exploring innovations in strategies and technologies aimed at expediting Monte Carlo simulations. It delves into the foundational concepts of various acceleration tactics, evaluates these strategies concerning their speed, accuracy, and practicality, and amalgamates a comprehensive overview and critique of acceleration methodologies for Monte Carlo simulations. Ultimately, the discourse envisages prospective trajectories for the employment of Monte Carlo techniques within the domain of tissue optics.

Red blood cells (RBCs) are the most abundant human blood cells. RBC aggregation and deformation strongly determine blood viscosity which impacts hemorheology and microcirculation. In turn, RBC properties depend on different endogenous and exogenous factors. One such factor is nitric oxide (NO), which is mainly produced by endothelial cells (EC) from L-arginine amino acid in the circulatory system. Since the mechanisms of the RBC-endothelium interplay are not clear up to date and considering its possible clinical importance, the aims of this study are to investigate in vitro: (1) The effect of L-arginine induced NO on RBC aggregation and adhesion to endothelium; (2) the NO effect on RBC aggregation and deformation induced by L-arginine and sodium nitroprusside without the presence of endothelium in the samples. The RBC aggregation and adhesion to a monolayer of EC were studied using optical tweezers (OT). The RBC deformability and aggregation without endothelium in the samples were studied using the flow chamber method and Myrenne aggregometer. We confirmed that NO increases deformability and decreases aggregation of RBCs. We showed that the soluble guanylate cyclase pathway appears to be the only NO signaling pathway involved. In the samples with the endothelium, the “bell-shaped” dependence of RBC aggregation force on L-arginine concentration was observed, which improves our knowledge about the process of NO production by endothelium. Additionally, data related to L-arginine accumulation by endothelium were obtained: Necessity of the presence of extracellular L-arginine stated by other authors was put under question. In our study, NO decreased the RBC-endothelium adhesion, however, the tendency appeared to be weak and was not confirmed in another set of experiments. To our knowledge, this is the first attempt to measure the forces of RBC adhesion to endothelium monolayer with OT.

Using a photosensitizer (PS), light, and oxygen, photodynamic therapy creates cytotoxic reactive oxygen species, such as singlet oxygen (1O2), that kill cancer cells. Many cancer cell lines have up to 300 times more folic acid receptors than healthy cells. Therefore, folic acid is often used to improve selectivity of PSs. Photobleaching poses a disadvantage for PSs. In this paper, we have studied the photoinduced changes of meso-substituted cationic pyridyl porphyrins in the presence of folic acid using fluorescence and absorption spectroscopy. In this work, it was demonstrated that L-histidine, which is a 1O2 quencher, and D-mannitol, which is a hydroxyl radical quencher, can reduce photobleaching of cationic porphyrins and their interaction products with FA. This implies both singlet oxygen and hydroxyl radicals are involved in photobleaching. Additionally, our study revealed certain important features of the photobleaching of cationic porphyrins in the presence of folic acid.

White matter, a densely packed collection of myelinated axons, plays an essential part in neural networks. With high spatial resolution and deep penetration, multi-photon microscopy (MPM) is promising for white matter imaging in animal models in vivo. The third harmonic generation (THG) signal can be generated from white matter, but the bottom part of the white matter layer generates weak THG due to its high scattering. Here, we demonstrate an in vivo labeling and imaging technology, capable of visualizing the white matter layer in the mouse brain, combining fluorescence labeling with MitoTracker Red and three-photon fluorescence (3PF) microscopy excited at the 1700 nm window. 3PF signals are several times higher than THG signals, resulting in deeper imaging of the white matter layer with the former. Our results indicate that 3PF microscopy is a promising technology for white matter imaging in the deep brain in vivo.

In-vivo flow cytometry is a noninvasive real-time diagnostic technique that facilitates continuous monitoring of cells without perturbing their natural biological environment, which renders it a valuable tool for both scientific research and clinical applications. However, the conventional approach for improving classification accuracy often involves labeling cells with fluorescence, which can lead to potential phototoxicity. This study proposes a label-free in-vivo flow cytometry technique, called dynamic YOLOv4 (D-YOLOv4), which improves classification accuracy by integrating absorption intensity fluctuation modulation (AIFM) into YOLOv4 to demodulate the temporal features of moving red blood cells (RBCs) and platelets. Using zebrafish as an experimental model, the D-YOLOv4 method achieved average precisions (APs) of 0.90 for RBCs and 0.64 for thrombocytes (similar to platelets in mammals), resulting in an overall AP of 0.77. These scores notably surpass those attained by alternative network models, thereby demonstrating that the combination of physical models with neural networks provides an innovative approach toward developing label-free in-vivo flow cytometry, which holds promise for diverse in-vivo cell classification applications.

There is a certain failure rate in traditional glaucoma surgery because of the lack of depth information in microscope images. In this work, we present a digital microscope-integrated optical coherence tomography (MIOCT) system and several custom-made OCT-compatible instruments for glaucoma surgery. Sixteen ophthalmologists were asked to perform trabeculectomy and canaloplasty on live porcine eyes using the system and instruments. After surgery, a subjective feedback survey about the user experience was taken. The experiment results showed that our system can help surgeons easily locate important tissue structures during surgery. The custom-made instruments also solved the shadowing problem in OCT imaging. Surgeons preferred to use the system in their future practice.