Proceedings Volume 12147

Tissue Optics and Photonics II

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Proceedings Volume 12147

Tissue Optics and Photonics II

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Volume Details

Date Published: 19 May 2022
Contents: 10 Sessions, 25 Papers, 17 Presentations
Conference: SPIE Photonics Europe 2022
Volume Number: 12147

Table of Contents

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Table of Contents

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  • Front Matter: Volume 12147
  • Skin Optics, Microcirculation, and Flowmetry
  • Light Propagation in Tissues, Modelling, and Optical Phantoms I
  • Light Propagation in Tissues, Modelling, and Optical Phantoms II
  • Speckle-based Techniques, Optical Coherence Tomography, and Tissue Elastography I
  • Speckle-based Techniques, Optical Coherence Tomography, and Tissue Elastography II
  • Vibrational Spectroscopy, Drug delivery, Photodynamic Therapies
  • Polarization Techniques and Microscopy
  • Multimodal Approaches
  • Poster Session
Front Matter: Volume 12147
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Front Matter: Volume 12147
This PDF file contains the front matter associated with SPIE Proceedings Volume 12147, including the Title Page, Copyright information, Table of Contents and Conference Committee list.
Skin Optics, Microcirculation, and Flowmetry
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Feasibility of videocapillaroscopy for characterization of microvascular patterns in skin lesions
Anastasia V. Guryleva, Alexander S. Machikhin, Demid D. Khokhlov, et al.
Identification of specific vascular patterns in skin formations is important for non-invasive differential diagnosis of benign and malignant tissues. Accurate blood vessel mapping and quantitative analysis of the vessels morphology may increase the diagnostic efficiency significantly in comparison to conventional dermatoscopy methods. In this paper, we propose videocapillaroscopy technique for non-invasive visualization of microvascular architecture right in the nevi area. It includes acquisition of skin lesion images by exoscope-based imaging system and their digital processing including non-uniformity correction, local and global stabilization, detection and quantification of vessels, comparison of the obtained vessel maps with the reference data. We have demonstrated the efficiency of microvascular network visualization in various melanocytic skin formations. Proposed technique may complement conventional dermatoscopy for diagnosing skin lesions and become especially effective in the early stages of diseases.
Skin oxygen saturation measurement using a non-contact optical device: optical phantoms development and metrological characterization
Julien Azzi, Philippe Arnoux, Hanène Mansour, et al.
In the current study, we perform the metrological characterization of the device called IPAM which is a non-contact optical device for the measurement of skin (cutaneous) oxygen saturation rate (ScO2) in the framework of critical limb ischemia. IPAM reflectance measurement is sensitive to the differential absorption spectra of oxy- and deoxyhemoglobin. Spectrophotometry was chosen as the gold standard method to measure the oxygen saturation rate of hemoglobin solutions: results validate the fact that the IPAM device is sensitive to the modification of hemoglobin oxygen saturation rate but also that it is able of measuring the same orders of magnitude of variations as the gold standard method. The metrological characterization on seven healthy volunteers showed that the IPAM device measurement precision is 0.83. Intra-individual variability was measured as significant for four out of the seven healthy volunteers. Inter-individual variability was proven to be statistically significant and ambient light showed no impact on the ScO2 measurements performed by the IPAM device. Such results will have to be taken into account in order to correctly interpret clinical data that will be acquired during a future clinical study: only variation of measurements greater than 0.83 will be interpreted as significant, measurements may be performed in any lighting environment (natural or artificial light, low or high-lighting environments) and data can be interpreted (e.g. as “normal” or “low” oxygen saturation rate) only in comparison with a reference skin zone from the same patient.
Light Propagation in Tissues, Modelling, and Optical Phantoms I
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Optical properties of Spectralon assessed by replication of literature data in Monte Carlo simulations
Diffuse reflectance spectroscopy is a popular technique for characterization of optically scattering materials and structures, including biological tissues and organs. In order to compensate for spectral properties of the incident light and/or detection setup, such measurements regularly involve a suitable reference sample, most often made from material with high reflectance throughout the included spectral region, aka. white standards (WS). It is therefore quite surprising that the absorption and reduced scattering coefficient for Spectralon, a very popular WS material for visible and NIR region (by Labsphere, North Sutton, NH), can not be found in literature. In the only report that we could find, they were estimated only for wavelengths above 600 nm. Moreover, the analysis was based on measurements performed on rather small samples and analytical predictions derived within the diffuse approximation of light transport, which raised some concerns about its accuracy. We have therefore performed dedicated Monte Carlo simulations of the relevant optical measurements on Spectralon samples reported in literature, i.e., the total reflectance as a function of the sample thickness and angular dependence of the diffuse reflectance at different wavelengths in visible and NIR. By varying the input properties until the model predictions matched the experimental data as well as possible, we could estimate the optical properties of Spectralon between 400 and 1100 nm. For the wavelength of 555 nm, e.g., our results indicate an absorption coefficient of 0.7 . 10–4 mm–1 and reduced scattering coefficient of 32 mm–1.
Comparative study of optical properties estimation on liquid optical phantoms using spatially-resolved diffuse reflectance spectroscopy and double integrating spheres methods
Whether for diagnosis, therapy or surgery, the estimation of optical properties (OP) of biological tissues is now of interest in the medical context. Indeed, optical methods are increasingly used in modern medicine, and these require knowledge of the behavior of light within the tissue. The presentation contribution aims to validate the estimation process of absorption and scattering coefficients values obtained using spatially-resolved diffuse reflectance (SR-DR) spectroscopy by comparing the obtained results with those of the reference double integrating spheres (DIS) technique. A set of nine optical phantoms based on methylene blue and intralipids allowing to tune absorption and scattering properties was prepared, from which diffuse reflectance spectra and integrating spheres measurements were acquired respectively. Work presented here reports both estimations approaches developed and highlights the relative spreads of optical properties between DR, DIS and theoretical values (i.e. according scatterer and absorber concentrations introduced in phantoms). This validation on optical bench will allow to later estimate the OP from in-vivo DR spectra acquired on skin samples, to assist the surgeon in non-invasively diagnosing the health status of a tissue around a skin carcinoma
Monte Carlo simulations to study light propagation through the skin of different phototypes
The propagation of light through biological tissues depends on its optical properties. These properties vary between individuals, tissues, and location; however, they are not considered to establish light dosimetry for therapies in clinical practice. In this context, this work aimed to use Monte Carlo (MC) simulations to evaluate how different skin phototypes influence light propagation and, consequently, the penetration depth. We use the Monte Carlo Extreme (MCX) implementation to simulate the photon trajectory. The skin model was composed of the following layers: living epidermis, papillary dermis, upper blood network dermis, reticular dermis, deep blood network, and subcutaneous fat. The skin layers’ optical properties were obtained directly from the literature, except for the absorption coefficient of the living epidermis, which was calculated based on the Petrov1 equation. This equation uses the wavelength, melanin and water concentrations, eumelanin/pheomelanin ratio, and other parameters to determine the absorption coefficient as a function of the melanin concentration. The melanin concentration value was varied from 0% to 50% to cover all six phototypes predicted on the Fitzpatrick scale. We also evaluated the effects at four different wavelengths: 410 nm, 630 nm, 780 nm, 850 nm. Our simulation results indicate that as the melanin concentration increases, the penetration depth decreases due to a higher absorption coefficient at the more superficial layers. This effect is more evident for lower wavelengths because biological components absorb more energy. They also show us that individual parameters can affect light propagation and need to be adjusted correctly. Thus, the development of individualized dosimetry can lead to a higher success rate for phototherapy. We also emphasize that skin phototype is not a parameter reported in most clinical studies papers, despite this being an important parameter that might influence clinical results, as this work shows. Thus, it is necessary to start paying attention to this characteristic and include it in phototherapy publications.
Quantification of the bulk optical properties of pear tissues for simulation of laser transmittance through intact pear
Insight in the transmission of laser light through intact fruit is important to understand and optimize the signals acquired with laser-based spectroscopy methods such as gas in scattering media absorption spectroscopy (GASMAS), which is based on tunable diode laser absorption spectroscopy (TDLAS). To this end, we quantified the bulk optical properties (BOP) of the different tissue layers (epidermis, outer cortex, inner cortex, and core) of Conference pear (Pyrus communis) samples using double integrating spheres measurements. A clear chlorophyll-a absorption feature was observed in the bulk absorption coefficient (μa) at 690 nm for the epidermis samples. At 761 nm, the bulk scattering coefficient (μs) decreased from the epidermis (256 ± 30.4 cm-1) towards the core (149 ± 12 cm-1) region where the difference between the cortex tissues and core was found to be negligible. The observed anisotropy factor (g) of the epidermis was lower than those of the other tissue layers (0.81 ± 0.026 vs. 0.94 ± 0.01). Next, Monte Carlo voxelized media (MCVM) simulations were performed based on these BOP values. As expected according to the Lambert-Beer law, the transmittance through the pear tissues increased exponentially for linearly decreasing layer thickness. Finally, these simulations were compared to transmittance measurements on pears using a GASMAS O2 sensor (operating at 761 nm), where the sample thickness was reduced by sequentially slicing the pear from the epidermis towards the center. It was found that the simulated transmittance based on the measured BOP followed the same trend as a function of the fruit thickness as the measured GASMAS transmittance. Therefore, these simulations can contribute to the optimization of the measurement configuration for O2 monitoring in intact pear fruit with GASMAS.
Evaluation of penetration depth of near-infrared irradiation generated by tunable ultra-short pulsed laser in ex vivo samples of mouse head
Optogenetic research has opened up the possibility to control neurons that will help detect and treat neurological diseases in the early stage. Treatment of dysfunctions requires exposure to a partial neural network accessible through the absorption of opsins or phytochromes expressed in the brain matter. The use of II-NIR USP lasers makes it possible to non-linear activate and deactivate photoactuators in neuronal cells through the skull. The possible obstacles for noninvasive stimulation are the limits in light penetration depth, scattering and absorption by biological tissues. This research aimed to investigate light propagation and penetration depth in skin, skull and brain matter of mouse head. To evaluate the light transmittance in brain tissues, we developed an experimental setup with a tunable ultra-short pulsed laser source operating at the wavelength range of 1.1-1.2 μm. This spectrum range corresponds to the spectra of nonlinear absorption of opsins/phytochromes and matches the second biological window where laser irradiation can penetrate the skin and skull bone without damaging and overheating them. The experimental results demonstrate that under certain conditions, the ultra-short pulsed laser radiation can reach a penetration depth with required power that will be sufficient for non-linear activation of opsins/phytochromes in the brain of living animals. These results could support applications of II-NIR USP laser in non-invasive optogenetics, photobiomodulation of the brain functioning and even neurological disorders diagnostics.
Light Propagation in Tissues, Modelling, and Optical Phantoms II
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Immediate subsurface skin blood flow monitoring using diffuse correlation spectroscopy: finite element simulations
Vysakh Vasudevan, Sujatha N.
Diffuse correlation spectroscopy (DCS) is an evolving optical modality that provides a fast, non-invasive, portable alternative to costly medical diagnostics in quantifying the blood flow. DCS involves monitoring the temporal statistics of scattered light from the sample, upon illumination by a coherent source. The detected signal is related to RBC motion, and blood flow is derived combining a model for photon propagation through the target tissue with the experimental observations. Conventionally, blood flow index (BFI) is calculated for long source-detector separations (SDS), that quantifies the blood flow from deeper tissue layers. Reduced SDS is required in measuring perfusion for immediate tissue subsurface, which is important in monitoring related changes. Here, we investigate the application of short-range DCS for skin blood flow monitoring and demonstrate the capability in determining BFI from immediate subsurface. Bilayer skin tissue with embedded micro vessels was modelled using finite element methods (FEM). Time correlated light diffusion equation was solved for this tissue geometry, with a point source illumination and autocorrelation plots were generated. Our in-silico analysis illustrates the change in BFI for varying blood flow rate and capillary depth from the skin surface. The work performed here, after experimental validation, is expected to have the potential for non-invasive quantitative blood flow assessment and can aid in diagnosing related skin disorders.
Spatial frequency domain imaging with a bucket detector
Armin J. M. Lenz, Pere Clemente, Vicent Climent, et al.
We present a single-pixel spatial frequency domain imaging (SP-SFDI) system where a single DMD (digital micromirror device) is used to modulate simultaneously the sinusoidal pattern for the spatial frequency sampling and the spatial sampling patterns to achieve spatial resolution. The detection system is therefore simplified to the point where it is replaced by an integrating sphere (IS) with a photodiode as a bucket detector. The characterization capabilities of this system are verified by imaging the absorption and reduced scattering coefficient of an inhomogeneous turbid media slab and of several moles of the forearm.
Contrast sensitivity at different background brightness levels and objective scattering index changes in patients before and after cataract removal surgery
Z. Jansone-Langina, R. Truksa, M. Ozolins, et al.
Purpose: Neurosensory vision tests can be an additional test to define the progression of cataract. Contrast vision tests can be a useful method to determine if the surgery is needed and the tests help to understand patient complaints about daily life tasks like driving. Our aim was to estimate the contrast vision sensitivity at different background levels and compare light scattering in patients before and after cataract surgery. Methods: Our research investigated 82 patients (73 eyes) with cataract and 56 (112 eyes) control group patients. The contrast sensitivity was measured with alternative forced choice test design (AFC) before and two weeks after Femto laser cataract surgery. The objective scattering index (OSI) was measured with HD Analyzer (Version 2.7.0.0). Contrast vision measurements were performed under mesopic conditions at different background brightness levels: 60 cd/m2 ; 85 cd/m2 ; 100 cd/m2 , and spatial frequencies:4 cpd; 6 cpd; 12 cpd; 18 cpd. Results: At the background brightness level 60, 85 and 100 cd/m2 there was statistically significant difference in all the spatial frequencies results, between all the groups (p<0.0001). The average OSI before the cataract surgery was 3.75 ± 1.62 units and OSI had a negative correlation with visual acuity (r=0.80) Conclusion Cataract-induced light scattering significantly decreased contrast sensitivity at all spatial frequencies There were no statistically significant differences between the Weber constants at the different background lighting levels, between all the groups. At a lighting level of 60 cd/m2 , cataract surgery provided significant improvement at the average spatial frequencies.
Speckle-based Techniques, Optical Coherence Tomography, and Tissue Elastography I
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Optical screening method to observe the biological activities of lentil (Lens culinaris) seeds quantitatively under the exposure of polyethylene microplastics (PEMPs) using ultrahigh accurate biospeckle optical coherence tomography
Seed germination rate and seedling growth differ based on environmental factors requiring non-invasive and non-contact seed screening techniques in agriculture. Moreover, the widespread usage and mismanagement of plastics have led to significant environmental problems affecting seed germination and seedling growth. Recently the attention of seed scientists and other biologists has been paid to optical sensing technologies-based measurements to observe the quality of seeds owing to the non-destructive and non-invasive detection capabilities. Moreover, the vigor of seeds is directly affected the crop yield. Therefore, here we propose to employ Biospeckle Optical Coherence Tomography (bOCT) in investigating the effect of polyethylene microplastics (PEMPs) on lentil seed germination. bOCT is a non-contact, nondestructive in vivo monitoring technique to visualize the change of internal activity of a biological object. Lentil seeds were exposed to PEMPs for 24 h bioassay with 10, 50, and 100 mg/L concentrations. The average speckle contrast was calculated after 0, 6, 12, and 24 h of exposure and statistically significant differences in bOCT contrast for all the treatments were observed just after 6 h of exposure. Thus, the results of the present study revealed that the presence of PEMPs significantly reduced the internal activity at the initial stages that could be visualized only because of the use of bOCT, in the early stage prior to the germination. Furthermore, this might be utilized as a trustworthy seed screening tool in the seed industry, which could save the screening time significantly compared to traditional approaches while assessing environmental pollution.
Biospeckle Optical Coherence Tomography (bOCT) reveals variable effects of acid mine drainage (AMD) on monocot and dicot seed germination
Acid mine drainage (AMD) is generated during the mineral extraction process. AMD contaminates farmland and rivers, so it makes sense to study the effects of AMD on crops. Since the conventional methods for studying plant responses to environmental stress are damaging and time-consuming, we propose the Biospeckle OCT (bOCT) method to evaluate the response of plants to AMD in a rapid and non-invasive way. In this study, we selected rice plant and soybean as experimental subjects. The seeds were exposed to 40 and 80 ml/L of simulated AMD solution, and the seed condition was monitored by bOCT. OCT images of the seeds were obtained at a speed of 10 frames per second for a few tens of seconds. For each pixel of the OCT structural images, the contrast across the temporal axis was calculated to give bOCT images. Meanwhile, we measured the root shoot length of rice and soybean after growing in AMD as a comparison. It was found that bOCT images clearly distinguished the changes in biological activities of seeds due to 40 and 80 ml/L of AMD treatments from those of control within much shorter time, 48 hours and 72 hours for soybean and rice, respectively, compared to the conventional method that failed to show any changes within the same time. And The seedling growing status of soybean and rice after 7 and 10 days showed the same trend as the bOCT results, respectively. This suggests that the proposed bOCT method can reveal the different responses of soybean and rice to different concentrations of AMD at a very early stage. This technique may be able to provide a reference indicator for studying plant response to environmental stress, and it is efficient and non-invasive.
Speckle-based Techniques, Optical Coherence Tomography, and Tissue Elastography II
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Speckle noise reduction of modulated images generated by spatial frequency domain imaging technique based on interferometric approach
Nowadays, optical imaging techniques have been broadly and successfully applied for biological screening and pathogen identification. Spatial Frequency Domain Imaging (SFDI) is a recent non-invasive wide-field optical imaging technique utilized in many medical and clinical procedures such as photodynamic therapy, assessing burn severity, and monitoring wound healing progression. The SFDI technique provides a quantitative mapping of tissue absorption and scattering properties over a wide field of view based on tissue diffuse reflectance/transmittance dependency on the spatial frequency. In a typical SFDI system, broadband light is employed as the illuminating source, whereas in some applications, laser sources could also be used. However, the appearance of laser speckle may influence the captured images and this, in turn, affects the accuracy of the reconstructed optical parameters. Therefore, in the current study, an experimental configuration based on interference has been utilized to reduce the speckle noise contrast of the obtained spatially modulated images. To achieve that, a red laser source with a wavelength of λ = 650 nm is divided into two identical beams using a beam splitter. One beam illuminates a reflecting mirror (reference beam) and the other one illuminates the reflecting window of a spatial light modulator (SLM) (reflected beam). Sinusoidal patterns of different frequencies are displayed on the SLM; hence the reflected beam becomes spatially modulated. The two beams (reference and reflected modulated beams) are combined to pass through a diffuser that simulates a rough tissue and imaged by a CCD camera. The obtained results reveal that the speckle noise contrast has been reduced by an average ratio of 21.89% after applying the interferometric configuration.
Unwanted movement bias evaluation for multiple exposure speckle imaging of blood flow using the synthetic exposure approach
Multiple exposure speckle imaging (MESI) allows to map relative blood flows at the surface of biological tissues. MESI is an extension of laser speckle contrast imaging (LSCI). It relies on the computation of speckle contrast K for several exposure times T, allowing to discriminate the contribution of static scatters (bulk tissues) from that of moving scatterers (red blood cells). First, we have evaluated how a synthetic exposure acquisition scheme could strongly simplify the instrument for MESI, while remaining quantitative over a range of relevant flows. A microfluidic chip with controlled flows in channels with dimension representative of mice brain cerebral vasculature has been imaged using the classical modulated intensities approach and the synthetic exposure mode. This study allowed to propose guidelines in terms of readout dark noise and spatial response uniformity for the choice of a camera for MESI in the synthetic exposure mode. Second, we have evaluated how unwanted movements introduce bias in the speckle contrast calculation for a representative range of movement speeds. Mixed solutions of intralipid and glycerin in Brownian motion have been characterized to provide calibrated samples in terms of scatterers de-correlation times. High concentration of glycerin led to decorrelation times of several ms corresponding to actual values in small capillaries while low concentration of glycerin led to decorrelation times of 1ms or less corresponding to arterioles and arteries. The effects of the unwanted movement speed and direction have been measured for both lateral (x-y) and axial (z) movements. The bias introduced by unwanted movement in the (x-y) plane depends on the relative values of the time between frames and the scatterers decorrelation. In addition, for axial movements, parameters such as the numerical aperture (NA) and the magnification level (M) need to be considered due to their role in defining the depth of field.
Vibrational Spectroscopy, Drug delivery, Photodynamic Therapies
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Temperature sensing during remote cargo release using polymer capsules modified with gold nanoparticles and nanodiamonds
Accurate thermal monitoring is essential tool for photothermal therapy or for application light-responsive drug delivery platforms, because overheating of living cells is related with unwanted side effects in surrounding tissues. In this work, we investigated a multifunctional polymer capsule embedded with nitrogen vacancies (NV) centers as nanothermometers and gold (Au) nanoparticles (NPs) as heating agents to perform of laser-induced release of bioactive compounds from the carriers with a simultaneous temperature measurements inside living cells.
Influence of annealing temperature on the cytotoxicity upconversion nanoparticles on different cell lines
R. A. Verkhovskii, R. A. Anisimov, M. V. Lomova, et al.
Carriers based on upconversion nanoparticles (UCNPs) and cyanine dye are suitable for theranostic application in oncology, although care must be taken for selection of the surface coating material, UCNP surface charge, size, and dosage of the material. Investigation of influence of annealing temperature of particles on the upconversion luminescence properties and cytotoxic effect are relevant. The present work demonstrates the assessment of cytotoxicity UCNPs unannealed and annealed at 550 oC on different normal and cancer murine cell lines in vitro. The cell viability is scored for cytotoxic effects of UCNPs at dark conditions. UCNPs provide a dose-dependent and time-dependent cytotoxic effect on all studied cell lines which was most pronounced for the Raw264.7 cell line. It is probably caused by the high phagocytic activity of macrophages. The statistically significant differences in cell viability after 24, 48 and 72 h of incubation of cells with particles were observed just for the macrophage cell line. It is also worth noting that annealed particles are less toxic than unannealed ones.
Polarization Techniques and Microscopy
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Solid tumors nanomechanical fingerprints and collagen-based optical signatures
Cancer progression is known to be accompanied by changes in mechano-cellular phenotype that reflected by changes in both the structure and mechanical properties of the tumor microenvironment (TME). Solid tumors, such as breast tumors and sarcomas, stiffen as they grow in a host healthy tissue. Stiffening is caused by an increase in the structural components of the tumor, mainly collagen fibers, and in cancer and stromal cells content. Tumor stiffening can cause blood vessel inefficiency and hypo-perfusion, and as a result, it poses major physiological barriers to the systemic delivery of drugs. Consequently, there is an urgent need for the development of novel biomarkers, that characterize the mechanical state of a particular tumor so as to support the development of novel therapeutic strategies that target the TME. In this work, polarized microscopy on picrosirius red stained tumor sections and immunofluorescence was used in order to assess collagen-based optical signatures in correlation to tumor progression, while Atomic Force Microscopy (AFM) was applied for the nano-mechanical characterization of the samples. Also, approved anti-fibrotic and chemotherapy drugs, were re-purposed so as to target the tumor matrix and alleviate stiffness The results demonstrated that solid tumors presents unique collagen-based signatures that can be combined with nanomechanical fingerprints so as to develop novel biomarkers for cancer prognosis and treatment monitoring.
Multimodal Approaches
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Optical needle biopsy for multimodal detection of the malignant liver tumours
At the moment, percutaneous needle biopsy (PNB) remains the gold standard for diagnosing liver cancer. However, the relatively high probability of false-negative results can still be an issue with the method. The introduction of real-time feedback for the precise navigation of the biopsy tool is an up-and-coming technology to immensely reduce the mistakes in taking relevant tissue samples. This work presents the technical details of the developed optical biopsy system, which implements fluorescence lifetime and diffuse reflectance measurements. Also, we demonstrate the most recent results of measurements by the system equipped with a novel needle optical probe, compatible with the 17.5G biopsy needle standard. At the first stage, measurements were verified in the murine model with inoculated hepatocellular carcinoma (HCC). With that model, we demonstrate that the registered set of independent diagnostic parameters allows us to reliably distinguish the HCC tissue, liver tissue in the control and the metabolically changed liver tissues of animals with the developed HCC tumour. At the second stage, the optical biopsy system was tested during the routing procedure of the transcutaneous biopsy in humans with suspected cancerous processes in the liver. Our results demonstrate that the developed technique can reliably discriminate malignant tumours of different nature (primary HCC and adenocarcinoma metastasis) from liver tissues. We conclude that, being supported by machine learning approaches, the presented technique can significantly decrease the rate of false-negative results for transcutaneous biopsy.
The effects of radiotherapy on tumour microvasculature: insights from optical coherence angiography and dynamic contrast-enhanced MR imaging towards adaptive radiation medicine
Stereotactic body radiotherapy (SBRT) shows promise for increasing local tumour control for many of the most lethal cancer types including pancreatic ductal carcinoma (PDA), compared to conventional radiotherapy. Yet SBRT radiation fractionation schedules may still be improved as its mechanism of action remains largely unknown. It has been suggested that this accelerated hypofractionated treatment benefits from vascular damage (in particular of blood capillaries ~10-30μm in diameter). We therefore hypothesize that monitoring radiation-induced microvascular changes will (1) yield insights into SBRT’s radiobiological effects, and (2) enable predictions of long-term tumour response. We addressed this hypothesis pre-clinically in PDA human xenografts grown in immunocompromised mice in a dorsal skinfold window chamber model. We monitored both micro- (via optical coherence tomography angiography (OCTA)) and macro- (via dynamic contrast enhanced magnetic resonance imaging (DCE-MRI)) vascular responses to irradiation over time. We first studied responses to single fraction irradiation, and then to a full typical clinical SBRT regimen delivered via a small animal irradiator. Candidate predictive vascular biomarkers of radiobiological relevance were derived from 3D OCTA microvascular networks (micro-scale response) and correlated with the DCE-MRI functional metrics relating to the transport of an MRI contrast agent (macro-scale response). The longitudinal trajectories of both were measured before, during and following treatments. Herein we focus primarily on the DLF150 and λ metrics from OCTA which describe the microvascular heterogeneity and molecular transport efficiency. To assess the predictive power of the various metrics, their temporal trends were compared to the macroscopic tumour response (volume and viability). Efforts are ongoing to train neural networks for this time series analysis. The combined OCTA and DCE-MRI insights should yield a better understanding of tissue functional response to high doses of radiation employed in SBRT and help develop improved SBRT fractionation schedules (dose and time combinations) towards personalized and adaptive radiation therapy.
Poster Session
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Elimination of single-beam substitution error in diffuse reflectance measurements using an integrating sphere revisited
In measurements of diffuse reflectance spectra (DRS) using an integrating sphere (IS), a highly reflective "white standard" (WS) is used to compensate for spectral properties of the incident light and detection setup. The DRS of the investigated sample is then obtained as the ratio between the values obtained with the sample and the white standard, calculated at each included wavelength. However, because the substitution of the WS with the sample may alter light fluence inside the IS, measured DRS are prone to a systematic distortion called single-beam substitution error (SBSE). An earlier report from our group1 has demonstrated a method for rigorous elimination of the SBSE based on additional measurements performed at the IS reference port. In addition, a more practical solution was presented, involving analytical correction of the measured DRS based on advance characterization of the specific IS. However, we have recently observed that such analytical correction can sometimes deviate from the rigorous experimental elimination of SBSE, depending on reflectance spectrum of the sample. In present study, we attribute this discrepancy to the spectral variation of diffuse reflectance of the IS inner wall, which was disregarded in the original derivation of the analytical correction. We describe experimental characterization of this spectral dependence, which improves the accuracy of analytical removal of SBSE for any object, regardless of its spectral properties.
The application of the multimodal approach for studying optical properties of bile in obstructive jaundice
Ksenia Kandurova, Nadezhda Golubova, Vadim Prizemin, et al.
This article describes the results of experimental studies using optical methods for in vitro estimation of the composition of bile obtained from patients with different etiologies of obstructive jaundice. Experimental studies were carried out using spectrophotometry and Raman spectroscopy methods to study and compare optical properties of bile from patients with obstructive jaundice caused either by choledocholithiasis or malignant tumors. The results show that the selected methods are suitable for studying the composition and optical properties of bile and can provide additional diagnostic information. Averaged Raman spectra, as well as absorption spectra of bile, corresponding to different etiologies of jaundice origin were demonstrated.
Direct optical generation of singlet oxygen in the regulation of vascular tone
An approach to visualization of the vascular bed with the possibility of assessing changes in blood filling and identifying diagnostically significant periodic changes in the signal by analyzing speckle images is proposed. The effect of singlet oxygen by direct excitation of an oxygen molecule by 1267 nm laser radiation on changes in the vascular bed parameters was studied using this approach.
Increasing the optical transparency of skeletal muscles via irradiation with IR lasers
Ahmed H. Sheet, Omnia Hamdy, Mohamed Abdel Harith
Optical diagnostics and imaging techniques have been widely spread in various biomedical and clinical applications. Although these techniques have the advantages of being safe and functional, most of them still suffer from relatively low resolution. The optical scattering and absorption properties strongly affect light penetration in biological tissues. Tissue optical parameters depend on the laser’s wavelength and control light propagation through tissues. However, optical clearing techniques have been proposed to control tissue scattering via equalizing the refractive index through the tissue components using chemicals of high refractive index. Such a procedure can reduce scattering within tissue and increase its optical transparency. Nowadays, tissue optical clearing can be achieved using different scenarios; physical, chemical, photo-chemical/photothermal, and compression, depending on the physical properties of the studied tissue or organ. The IR lasers are utilized in many medical applications, such as photodynamic therapy and bio-stimulation. Additionally, low-intensity infrared lasers cause small heating, leading to tissue water evaporation and increasing optical transmittance. In the present study, tissue optical transmittance has been evaluated after exposure to different IR laser wavelengths. The collimated transmittance of bovine skeletal muscle samples has been monitored using a 650-nm incident laser. The samples have been irradiated with IR lasers at 785 and 980 nm for different periods (A total of 75 min divided into periods of 15 min). The results show that tissue transmittance increased by 27% and 36.7% after irradiation for 75 min with 785 and 980 nm, respectively. Additionally, the optical microscopic images of the 980-nm irradiated samples show higher resolution than native samples.
3D bladder models for fluorescence imaging on bimodal system
For a favorable treatment result, early diagnosis of pathological cancerous micro-areas with their subsequent removal is highly important and can be achieved by the development of new modeling techniques and conducting relevant experiments. Various models of the bladder can be developed and applied to provide a platform for studying, processing and improving the signals received from various video systems. Here, in order to study visualization properties at fluorescence endoscopy, 3D optical phantoms of urinary bladder have been developed. The phantoms simulated optical properties of the bladder wall, including localized areas that represent tumor tissues and contained PpIX photosensitizer at various concentrations for fluorescence "diagnostics". To perform bimodal fluorescence imaging, a two-channel video fluorescence system was used. First, intraoperative images of the bladder wall were obtained in a patient with bladder cancer. A video system was used to reveal and image pathological areas with increased fluorescence intensity. Fluorescence indices in tumor tissue were recorded and corresponded to different concentrations of PpIX photosensitizer. Then, a bimodal fluorescence imaging was performed on 3D phantoms. The obtained images and fluorescence intensity measurements showed the ability of the video fluorescence system to register bladder wall structures and accumulated in them photosensitizers in concentrations from 0.25 to 20 mg/kg. The developed models can serve as a useful instrument for test measurements for constructing multimodal mosaic panoramic images of the bladder surface. This will help to advance in solving problems of endoscopic image processing using bimodal imaging, which uses diagnostic (fluorescence) and color channels.