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A novel two-stage technique to fabricate silicon nanoparticles is reported. At the first stage, silicon nanowire arrays are formed by metal-assisted chemical etching. At the second stage, the nanoparticles are produced by pulsed laser ablation of the silicon nanowire targets in water and ethanol. The fabricated particles have relatively small mean size in the range of 24 – 45 nm depending on the used buffer liquid. The ablation threshold of the silicon nanowire arrays is 2 – 11 times smaller than that for crystalline silicon targets. Owing to the achieved parameters, the proposed technique is more efficient in comparison with traditional approaches of mechanical milling of silicon nanowires and laser ablation of crystalline silicon. Raman spectroscopy study revealed crystalline structure of the fabricated silicon nanoparticles. The properties of the produced nanoparticles indicate their high potential in biophotonics.

Simple Summary Fluorescence imaging is an efficient tool in monitoring photodynamic therapy procedures allowing us to track accumulation and photobleaching of a photosensitizer (PS). Chlorin-based PSs feature high absorption in the red and blue bands of visible spectrum. Due to spectral dispersion of light penetration depth in biotissues, fluorescence signals registered upon excitation by red or blue light are formed in different measurement volumes. We present analytical and numerical models of dual-wavelength fluorescence imaging for evaluation of PS localization depth in the cases of topical administration and intravenous injection. The results of analytical and numerical simulations are in good agreement with the phantom experiments, and are translated to the in vivo imaging, which allows to interpret experimental observations in animal trials, human volunteers, and clinical studies. The proposed approach allows us to noninvasively estimate typical accumulation depths of PS localization which are consistent with the morphologically expected values. Abstract Fluorescence imaging modalities are currently a routine tool for the assessment of marker distribution within biological tissues, including monitoring of fluorescent photosensitizers (PSs) in photodynamic therapy (PDT). Conventional fluorescence imaging techniques provide en-face two-dimensional images, while depth-resolved techniques require complicated tomographic modalities. In this paper, we report on a cost-effective approach for the estimation of fluorophore localization depth based on dual-wavelength probing. Owing to significant difference in optical properties of superficial biotissues for red and blue ranges of optical spectra, simultaneous detection of fluorescence excited at different wavelengths provides complementary information from different measurement volumes. Here, we report analytical and numerical models of the dual-wavelength fluorescence imaging of PS-containing biotissues considering topical and intravenous PS administration, and demonstrate the feasibility of this approach for evaluation of the PS localization depth based on the fluorescence signal ratio. The results of analytical and numerical simulations, as well as phantom experiments, were translated to the in vivo imaging to interpret experimental observations in animal experiments, human volunteers, and clinical studies. The proposed approach allowed us to estimate typical accumulation depths of PS localization which are consistent with the morphologically expected values for both topical PS administration and intravenous injection.

Cerebrovascular imaging of rodents is one of the trending applications of optoacoustics aimed at studying brain activity and pathology. Imaging of deep brain structures is often hindered by sub-optimal arrangement of the light delivery and acoustic detection systems. In our work we revisit the physics behind opto-acoustic signal generation and perform theoretical evaluation of optimal laser wavelengths with an aim of enabling whole brain cerebrovascular optoacoustic angiography in small rodents. A comprehensive model based on diffusion approximation was developed to simulate optoacoustic signal generation using optical and acoustic parameters closely mimicking a typical murine brain and surrounding tissues. The model revealed three characteristic wavelength ranges in the visible and near-infrared spectra optimally suited for imaging cerebral vasculature of different size and depth. The theoretical conclusions are confirmed by numerical simulations while in vivo imaging experiments further validated the capacity for accurately resolving brain vasculature at depths ranging between 0.7 and 7 mm.

Development of a number of diseases is accompanied by changes in the blood vessels’ structure and the investigation of tissue vascular pattern remains one of the most essential problems in experimental and clinical medicine. Hybrid methods of optoacoustic (OA) imaging enable label-free optical-contrast angiography at optical penetration depths with ultrasonic resolution. We used OA to study vascular network of experimental tumor during growth and after treatment as well as to study the dynamics of blood content of human skin during functional tests. Optoacoustic angiography was performed using raster-scan system in reflection mode with 532 nm laser source and wideband PVDF detector. The sensitivity of the system allowed to visualize 50 µm blood vessels at up to 2.1 mm depth. Minimally detected diameter of blood vessel located at the surface of a soft tissue was 15 µm. Imaging of colon tumor models CT26 and HT-29 revealed peculiarities of vascular system development. Irradiation-induced increase of small tumor vessels segments number and parallel decrease in the number of large hemoglobin-containing structures were demonstrated. The fraction of blood-filled vessels of the human skin was assessed during cuff occlusion and temporarily filling with blood became clearly visible on OA images. To study the effects of local mechanical compression on human skin vasculature we varied external pressure and revealed the gradual drop in OA signal from blood vessels. We demonstrated the possibilities of raster-scan angiography for in vivo analysis of vessels structure, for monitoring of neoangiogenesis and for dynamical investigation of blood content under external actions.

The effect of the formation of deep minima in frequency characteristics of photon density waves (PDWs) during their propagation in scattering media with different optical characteristics has been studied by statistical Monte Carlo modeling. The simulation was performed for the Henyey–Greenstein scattering phase function with the anisotropy factor value varying in the range of 0–0.93. The dependence of the position and magnitude of the minimum in the frequency response of PDWs on the combination of the parameters of the scattering medium and the distance to the radiation source is demonstrated.

The frequency characteristics of spherical photon density waves excited in media with different degrees of scattering anisotropy are studied. Statistical modeling of the frequency and phase responses of the spatial irradiance of the light field emitted by a point-sized isotropic source were performed employing the Monte Carlo technique. The scattering anisotropy of the medium was determined by the Henyey–Greenstein phase function with different values of the mean scattering cosine. It is shown that the scattering anisotropy factor determines the frequency range, in which the effect of the photon path length distribution on the magnitude of the photon density wave dispersion is maximal. In media with quasi-isotropic scattering, dispersion effects are manifested at lower frequencies as compared to those for anisotropic media. The simulation results are compared with the analytical solution for the asymptotic regime of the light field in an isotropically scattering medium.

We report on a novel approach to monitor photodynamic therapy procedure based on the simultaneous fluorescence and optoacoustic imaging with the use of a liposome nanoconstructs contain benzoporphyrin derivatives and the fluorescent IRDye800 dye. We demonstrate the results of a preliminary in vivo study with combined fluorescence and optoacoustic custom-made setups on a NUDE mouse with human glioblastoma U-87.

Modern trends in optical bioimaging require novel nanoproducts combining high image contrast with efficient treatment capabilities. Silicon nanoparticles are a wide class of nanoobjects with tunable optical properties, which has potential as contrasting agents for fluorescence imaging and optical coherence tomography. In this paper we report on developing a novel technique for fabricating silicon nanoparticles by means of picosecond laser ablation of porous silicon films and silicon nanowire arrays in water and ethanol. Structural and optical properties of these particles were studied using scanning electron and atomic force microscopy, Raman scattering, spectrophotometry, fluorescence, and optical coherence tomography measurements. The essential features of the fabricated silicon nanoparticles are sizes smaller than 100 nm and crystalline phase presence. Effective fluorescence and light scattering of the laser-ablated silicon nanoparticles in the visible and near infrared ranges opens new prospects of their employment as contrasting agents in biophotonics, which was confirmed by pilot experiments on optical imaging.

A novel approach to monitor photosensitizer accumulation and photobleaching in the course of photodynamic therapy (PDT) with the use of nanoconstructs based on the simultaneous fluorescence (FL) and optoacoustic (OA) imaging is implemented. A liposome nanoconstructs employed in this studies contain benzoporphyrin derivatives (BPD) which serve as a photosensitizer and secondly, as a fluorophore, and the fluorescent IRDye800 dye acting as an additional contrasting agent due to its high quantum yield. FL provides visualization of BPD and IRDye800 distribution, while OA principle allows for BPD-absorption based imaging of tumor and its vascular environment. We demonstrate the results of a preliminary in vivo study with combined FL and OA custom-made setups on a NUDE mouse with human glioblastoma U- 87. The results of this studies show a hemorrhage in the tumor area on the OA images obtained @532 nm after PDT that is not visually detected, but confirmed with the following histological verification. Fast nanoconstructs accumulation (< 10 min) was observed using FL imaging with the concentration in tumor only 10% higher than in surrounding tissues. We believe that the ratio of nanoconstructs accumulation in tumor can be significantly increased using target approach.

Modern optical imaging techniques demonstrate significant potential for high resolution in vivo angiography. Optoacoustic angiography benefits from higher imaging depth as compared to pure optical modalities. However, strong attenuation of optoacoustic signal with depth provides serious challenges for adequate 3D vessel net mapping, and proper compensation for fluence distribution within biotissues is required. We report on the novel approach allowing to estimate effective in-depth fluence profiles for optoacoustic systems. Calculations are based on Monte Carlo simulation of light transport and account for complex illumination geometry and acoustic detection parameters. The developed fluence compensation algorithm was tested in in vivo angiography of human palm and allowed to overcome significant in-depth attenuation of probing radiation and enhance the contrast of lower dermis plexus while preserving high resolution of upper plexus imaging.

Cerebrovascular imaging of rodents is one of the trending applications of optoacoustics aimed at studying brain activity and pathology. Imaging of deep brain structures is often hindered by sub-optimal arrangement of the light delivery and acoustic detection systems. In our work we revisit the physics behind opto-acoustic signal generation for theoretical evaluation of optimal laser wavelengths to perform cerebrovascular optoacoustic angiography of rodents beyond the penetration barriers imposed by light diffusion in highly scattering and absorbing brain tissues. A comprehensive model based on diffusion approximation was developed to simulate optoacoustic signal generation using optical and acoustic parameters closely mimicking a typical murine brain. The model revealed three characteristic wavelength ranges in the visible and near-infrared spectra optimally suited for imaging cerebral vasculature of different size and depth. The theoretical conclusions are confirmed by numerical simulations while in vivo imaging experiments further validated the ability to accurately resolve brain vasculature at depths ranging between 0.7 and 7 mm.

We report on developing a technique for fabricating silicon nanoparticles by laser ablation of porous silicon and silicon nanowires in liquids that have potential for image contrasting in fluorescence imaging and optical coherence tomography.

The parameters of an echo signal from the underwater lidar are studied for the case of modulation of a probing pulse by a high frequency signal with a frequency linearly varying with time. The analysis is based on the statistical Monte Carlo simulations of the frequency and phase responses of a signal propagating along the emitter-water-reflector-water-receiver path and an analytical representation of the signal as a pulse described by a Gaussian function with intrapulse modulation. Delays and pulse shape changes caused by temporal dispersion of the photon-density waves are estimated. It is shown that the temporal dispersion effect reduces the efficiency of the matched processing of a complex signal in the receiving system.

In this study we present a complex approach to photodynamic therapy (PDT) with chlorin based photosensitizers including Monte Carlo based planning and prediction of optical diagnostics results, intra-procedure dual-wavelength fluorescence monitoring allowing to evaluate PS accumulation and photobleaching, and monitoring of tissue response with optical coherence tomography (OCT). The approach was employed to compare the effects of different PDT regimens in normal and tumor tissues and the results of non-invasive optical diagnostics were matched with results of histologic examination, including hematoxylin-eosin and Mallory staining. The considered doses are in the range 50-150 J/cm2 for normal tissues and 150-275 J/cm2 for tumor tissues, single wavelength (405 and 660 nm) and dual-wavelength regimes are studied.

Dual-wavelength photodynamic therapy is a photodynamic therapy (PDT) modality combining therapeutic effects of irradiation at two wavelengths of different region of visible range. In this paper we report on comparative analysis of single- and dual-wavelength PDT regimes based on multimodal optical monitoring of tissue response with histologic verification. Morphological and functional tissue responses to PDT procedure with chlorin-based photosensitizer (PS) were studied at the normal skin of a rabbit ear inner surface. Multimodal optical monitoring was performed by OCT and dual-wavelength fluorescence technique. The studied doses vary from 50 to 150 J/cm2 delivered separately at 405 or 660 nm, or at both wavelengths together in the equal dose.

A dual-wavelength 532/1064 nm optoacoustic (OA) imaging system allows 3D visualizations of arteriovenous anastomoses (AVAs) with an acoustic spatial resolution (50 µm) at depths of up to 2 mm in vivo in rabbit ears. Both structural and spectral information from the OA data are employed to analyze the anatomical locations of the blood vessels and to distinguish between veins and arteries in the zone of their confluence. The OA monitoring of a rabbit ear under temperature-induced (43 °C/15 °C) shunting demonstrated the potential of the technique for the monitoring of functional arteriovenous anastomosis.

Optical coherence tomography (OCT) is a modern technique for imaging of internal structures of biotissue of up to several millimeters in depth with a resolution of several micrometers. However, various external conditions can distort the diagnostic capabilities of an OCT image. Mechanical compression and temperature regime are the two conditions which mostly affect the diagnostic OCT images obtained with a contact probe. It is shown here that the application of compression to human skin induces a decrease in contrast of the stratum corneum-epidermis junction and an increase in contrast of the epidermis-dermis junction. With regard to these junctions, a preliminary change of biotissue temperature induces additional changes in the contrast, with opposing effects in case of heating and cooling.

The goal of this study is a comparative analysis of the efficiency of the PDT protocols for CT26 tumor model treatment in Balb/c mice employing red and blue light with both topical and intravenous administration of chlorin-based photosensitizers (PSs). The considered protocols include the doses of 250 J/cm2 delivered at 660 nm, 200 J/cm2 delivered at 405 nm, and 250 J/cm2 delivered at both wavelengths with equal energy density contribution. Dual-wavelength fluorescence imaging was employed to estimate both photobleaching efficiency, typical photobleaching rates and the procedure impact depth, while optical coherence tomography with angiography modality (OCT-A) was employed to monitor the tumor vasculature response for up to 7 days after the procedure with subsequent histology inspection. Red light or dual-wavelength PDT regimes with intravenous PS injection were demonstrated to provide the most pronounced tumor response among all the considered cases. On the contrary, blue light regimes were demonstrated to be most efficient among topical application and irradiation only regimes. Tumor size dynamics for different groups is in good agreement with the tumor response predictions based on OCT-A taken in 24h after exposure and the results of histology analysis performed in 7 days after the exposure.

Chronic rhinitis (CR) is among the most frequent inflammatory diseases of ear-nose-throat (ENT) covering up to 30% of the population. Different forms of CR require different treatment tactics, which indicates the need for an efficient tool for differential diagnostics of CR. Optical coherence tomography (OCT) is a promising tool for fast non-invasive evaluation of nasal mucosa, which, however, requires further interpretation of the obtained diagnostic image. In this paper, we provide a comparative analysis of several machine learning approaches that aim at automated differential diagnostics of CR based on diagnostic OCT images of 78 patients aged between 28 and 74 ages. Gradient boosting decision trees (GBT) approach reveals the best classification accuracy (98% and 94% for binary and diagnostic classification, respectively). It shows that proposed approaches have potential for automated classification of CR OCT images.

The spatial-angular and temporal characteristics of the radiance of the light field emitted by a nonstationary point isotropic source in sea water are studied. Using the Monte Carlo method, we calculated the pulse transfer functions and frequency responses of the angular radiance distributions at various distances from the source. Particular integral characteristics of the angular radiance distributions are estimated. It is shown that with an increase in the delay time, measured from the time of arrival of ballistic photons, the angular radiance distribution asymptotically tends to be isotropic. The frequency and phase responses of the alternating radiance component from a source modulated by power at a high frequency are studied. It is shown that with an increase in the modulation frequency, the angular distribution of the alternating radiance component is concentrated close to the direction to the source.

We developed a compact, hand-held hyperspectral imaging system for 2D neural network-based visualization of skin chromophores and blood oxygenation. State-of-the-art micro-optic multichannel matrix sensor combined with the tunable Fabry-Perot micro interferometer enables a portable diagnostic device sensitive to the changes of the oxygen saturation as well as the variations of blood volume fraction of human skin. Generalized object-oriented Monte Carlo model is used extensively for the training of an artificial neural network utilized for the hyperspectral image processing. In addition, the results are verified and validated via actual experiments with tissue phantoms and human skin in vivo. The proposed approach enables a tool combining both the speed of an artificial neural network processing and the accuracy and flexibility of advanced Monte Carlo modeling. Finally, the results of the feasibility studies and the experimental tests on biotissue phantoms and healthy volunteers are presented.

This editorial provides an introductory overview for the Special Section on Topical Problems of Biophotonics.

We introduce a portable hand-held hyperspectral imaging system for the functional diagnostics of skin and vascular system. Hyperspectral image analysis aided by artificial neural networks (ANN) allows to reconstruct major physiological parameters of human skin nearly in real-time. The developed device provides spatial distribution of blood volume fraction, oxygenation and melanin content within skin. Special attention has been paid on the system validation and calibration using specially developed skin mimicking phantoms with confirmed optical properties. The device was built on the basis of unique hyperspectral snapshot camera utilizing a micro Fabry-Perot filter providing real spectral response in each pixel (no interpolation is used in image formation). A broadband illumination unit combined with the camera is based on the fiber-optic illuminator providing uniform distribution of light intensity and utilizes halogen lamp. The specially developed ANN algorithm was used to perform the inverse problem solution for quantitative assessment of major parameters of skin based on the measured hyperspectral images. A set of diffuse reflectance spectra of human skin imitated by the Monte Carlo method developed in-house has been used extensively for the training of ANN. The volume fraction of blood, oxygen saturation, melanin content and thickness of the epidermal layer were used variable parameters in the utilized seven-layer Monte Carlo-based skin model. The total training set contained 45,198 spectra in the range of 505–800 nm simulated with a step of 5 nm. The developed imaging system has been successfully used to perform the occlusion test measurements with healthy volunteers.

Characteristics of different underwater imaging systems are compared based on the results of Monte Carlo simulations of light transport in the sea water. The consideration includes systems with continuous-wave illumination, modulated illumination, pulsed systems with time gating detection, and hybrid systems with probing pulse modulated at high frequency. To generalize the study, the ratio of SNRs of different systems when imaging a sinusoidal test pattern is analyzed. Pulsed systems are demonstrated to provide higher SNR as compared to continuous-wave systems for typical imaging distances varying in the range 35-60 m, while systems with modulated illumination provide a SNR comparable to that for continuous-wave systems. Hybrid systems provide SNRs comparable to that in pulsed systems benefiting, however, from higher contrast transfer coefficient.

The fluorescence imaging device for localizing a tumor in a patient's body and monitoring photobleaching of a photosensitizer (PS) in course of photodynamic therapy was constructed. The system includes two LED sources at 405 and 660 nm for excitation of chlorine-based PSs. The ratio of fluorescence signals upon excitation at these wavelengths was demonstrated to provide evaluation of PS penetration depth in biotissues after topical administration. The study included Monte Carlo simulations that are in a good agreement with phantom experiment.

The paper reviews our recent experience in multiscale biomedical optoacoustic imaging using wideband ultrasonic detectors based on polyvinylidene fluoride films. The experimental setups for optoacoustic microscopy and tomography are presented, numerical algorithms for versatile characterization of tissue vasculature are discussed.

We propose a hybrid approach to image enhancement in acoustic resolution photoacoustic microscopy. The developed technique is based on compensation for nonuniform spatial sensitivity of the optoacoustic (OA) system in both optical and acoustic domains. Spatial distribution of optical fluence is derived from full three-dimensional Monte Carlo simulations accounting for conical geometry of tissue laser illumination at the wavelength of 532 nm. Approximate nonuniform spatial response of acoustic detector with numerical aperture of 0.6 is derived from the two-dimensional k-Wave modeling. Application of the developed technique allows to improve the spatial resolution and to balance in-depth signal-level distribution in OA images of phantom and in-vivo objects.

Backscatter signal formation in underwater lidar systems is studied and temporal and frequency characteristics are analyzed using the Monte Carlo technique. Both frequency and phase responses of the backscattered signal demonstrate similar dependencies, showing stronger frequency dependence in the high-frequency range. The beats of the frequency response due to dephasing of corresponding spectral harmonics are shown in the high-frequency range. Results of Monte Carlo simulations of the backscattered signal are in good agreement with the approximate analytical expression derived in the small-angle approximation; however, frequency responses calculated by the Monte Carlo technique and by small-angle approximation demonstrate a difference in the high-frequency range due to interference effects, while the phase response demonstrated good agreement in the entire frequency range.

The ratio of fluorescence signals upon excitation of chlorine-based photosensitizers at peaks of 402 and 662 nm provides evaluation of photosensitizer penetration depth in biotissues. Monte Carlo simulations are in good agreement with phantom experiment.

The results of optoacoustic calibration-free measurements of effective optical attenuation of whole blood in vitro at 532-1069 nm wavelengths are presented. The potential of multiscale optoacoustic in vivo measurements of blood oxygen saturation is discussed.

Optical transfer functions of underwater imaging systems employing narrow pulses or sinusoidally modulated beams for image formation are studied. A modified Monte Carlo technique allowing for direct statistical modeling of these functions accounting for temporal dispersion is proposed and implemented. The optical transfer functions are calculated for various modulation frequencies of the illumination beam and for the case of pulsed illumination. The employment of high-frequency sinusoidal or pulsed modulation with consistent processing of the received signal is shown to significantly increase the contrast sensitivity of underwater imaging systems as compared with systems with stationary illumination.

Modern gynecologic practice requires noninvasive diagnostics techniques capable of detecting morphological and functional alterations in tissues of female reproductive organs. Optical coherence tomography (OCT) is a promising tool for providing imaging of biotissues with high resolution at depths up to 2 mm. Design of the customized probes provides wide opportunities for OCT use in gynecology. This paper contains a retrospective insight into the history of OCT employment in gynecology, an overview of the existing gynecologic OCT probes, including those for combination with other diagnostic modalities, and state-of-the-art application of OCT for diagnostics of tumor and nontumor pathologies of female genitalia. Perspectives of OCT both in diagnostics and treatment planning and monitoring in gynecology are overviewed.

Optical coherence tomography (OCT) is currently actively introduced into clinical practice. Besides diagnostics, it can be efficiently employed for treatment monitoring allowing for timely correction of the treatment procedure. In monitoring of photodynamic therapy (PDT) traditionally employed fluorescence imaging (FI) can benefit from complementary use of OCT. Additional diagnostic efficiency can be derived from numerical processing of optical diagnostics data providing more information compared to visual evaluation. In this paper we report on application of OCT together with numerical processing for clinical diagnostic in gynecology and otolaryngology, for monitoring of PDT in otolaryngology and on OCT and FI applications in clinical and aesthetic dermatology. Image numerical processing and quantification provides increase in diagnostic accuracy. Keywords: optical coherence tomography, fluorescence imaging, photod

A new approach to optical measuring blood oxygen saturation was developed and implemented. This technique is based on an original three-stage algorithm for reconstructing the relative concentration of biological chromophores (hemoglobin, water, lipids) from the measured spectra of diffusely scattered light at different distances from the probing radiation source. The numerical experiments and approbation of the proposed technique on a biological phantom have shown the high reconstruction accuracy and the possibility of correct calculation of hemoglobin oxygenation in the presence of additive noise and calibration errors. The obtained results of animal studies have agreed with the previously published results of other research groups and demonstrated the possibility to apply the developed technique to monitor oxygen saturation in tumor tissue.

The present paper is a retrospective review of the development of the approach to numerical modeling of radiation propagation in biological tissues, based on the use of finite difference methods for the solution of the radiative transfer equation (RTE) and its application to the problems of biomedical diagnostics. The advantage of finite difference methods is the possibility to obtain the solution of the direct problem of radiation propagation in turbid media, when the exact analytical solution is impossible. In turn, the possibility to solve the RTE opens wide perspectives for the solution of inverse problem and reconstruction of structural and functional characteristics of objects from the detected scattered radiation. We present a review of the finite difference methods applied to the solution of angiography problems and investigation of blood using optical biomedical diagnostic technologies.

Diffuse optical spectroscopy (DOS) and its modification employing structured illumination are widely used in monitoring biotissue oxygenation. In such measurements it is important to know the probing volume for definite source-detector configuration; however, it cannot be measured directly. Monte Carlo simulations allow to trace the probing depth of each individual photon contributing to the signal, which provides a numerical solution for this problem. In this study we investigate distributions of photons over maximal depth reached in turbid media (probing depth) with optical parameters typical for cutaneous tissues at the wavelength of 600 nm. Different configurations of probing illumination are considered, such as collimated point source, one-dimension sinusoidal and rectangular patterns. For collimated point source and zero source-detector separation the number of collected photons monotonously decreases with the probing depth while a pronounced maximum in the distribution is manifested with the increase of source-detector separation. The position of this maximum shifts to higher depths with the decrease of µ a . For one-direction sinusoidal and rectangular illumination patterns it is shown that when the photons are collected near the center of a bright stripe, the peak of the distribution remains close to the surface. When the photons are collected near the center of a dark stripe the peak shifts towards higher depths with the decrease in spatial duty cycle and spatial frequency of the illumination pattern. Employment of rectangular illumination pattern seems more efficient for DOS applications due to wider abilities for controlling probing depth.

The main goal of the study was a vasculature targeted PDT. A new approach named M-mode-like OCT (MML OCT) was applied to monitor early response to PDT. Due to the chosen filtering parameters (96 Hz filter threshold), this approach visualizes only vessels with flowing blood. Without flowing blood even filled vessels are not visualized because flow-less blood causes speckle variations with significantly lower frequencies (

Two pronounced absorption peaks in blue and red ranges of the chlorin-based photosensitizer (PS) absorption spectrum provide additional benefits in photodynamic therapy (PDT) performance. Differing optical properties of biological tissues in these ranges allow for both dual-wavelength diagnostics and PDT performance. We provide a comparative analysis of different PDT regimes performed with blue and red lights and their combination, with doses varying from 50 to 150 J/cm2. The study was performed on the intact skin of a rabbit ear inner surface, with the use of chlorin e6 as a PS. PDT procedure protocol included monitoring of the treated site with fluorescence imaging technique to evaluate PS accumulation and photobleaching, as well as with optical coherence tomography (OCT) to register morphological and functional responses of the tissue. Optical diagnostic observations were compared with the results of histopathology examination. We demonstrated that PDT procedures with the considered regimes induce weaker organism reaction manifested by edema in normal tissue as compared to irradiation-only exposures with the same light doses. The light doses delivered with red light induce weaker tissue reaction as compared to the same doses delivered with blue light only or with a combination of red and blue lights in equal parts. Results of in-vivo OCT monitoring of tissue reaction are in agreement with the results of histopathology study.

Increase of the efficiency of photodynamic therapy (PDT) requires the development of advanced protocols employing both novel photosensitizer (PS) carriers and aids for online monitoring. Nanoconstructs may be comprised of a photosensitizer, chemotherapy drugs, or inhibitors of molecular pathways that support cancer growth. In this paper, we analyze the efficiency of a bimodal approach involving fluorescence and optoacoustic imaging in monitoring drug distribution and photobleaching. The study evaluates typical sensitivities of these techniques to the presence of the two key moieties of a nanoconstruct: benzoporphyrin derivatives (BPD) serving as a PS, and IRDye800 acting as a contrast agent. Both imaging modalities employ dual-wavelength probing at the wavelengths corresponding to absorption peaks of BPD and IRDye800, which enables their separate detection. In an experiment on a tissue-mimicking phantom with inclusions containing separate BPD and IRDye800 solutions, fluorescence imaging demonstrated higher contrast as compared to optoacoustic imaging for both components, though strong light scattering in the surrounding media restricted accurate localization of the markers. It was also sensitive to photobleaching, which is a measure of PDT efficiency. Optoacoustic imaging demonstrated sufficient sensitivity to both components, though less than that of fluorescence imaging, however, it enabled depth-resolved detection of an absorber and estimation of its relative content. Employment of the bimodal approach in monitoring of PS photobleaching adds to its potential in intraprocedural PDT monitoring.

The structure of a light field in sea water excited by a unidirectional point-sized pulsed source is studied by Monte Carlo technique. The pulse shape registered at the distances up to 120 m from the source on the beam axis and in its axial region is calculated with a time resolution of 1 ps. It is shown that with the increase of the distance from the source the pulse splits into two parts formed by components of various scattering orders. Frequency and phase responses of the beam are calculated by means of the fast Fourier transform. It is also shown that for higher frequencies, the attenuation of harmonic components of the field is larger. In the range of parameters corresponding to pulse splitting on the beam axis, the attenuation of harmonic components in particular spectral ranges exceeds the attenuation predicted by Bouguer law. In this case, the transverse distribution of the amplitudes of these harmonics is minimal on the beam axis.