Measurement of tissue optical properties in the context of tissue optical clearing

Influence of optical clearing agents on the scattering properties of human nail bed and blood microrheological properties: In vivo and in vitro study

Optical clearing agents (OCAs) are substances that temporarily modify tissue's optical properties, enabling better imaging and light penetration. This study aimed to assess the impact of OCAs on the nail bed and blood using in vivo and in vitro optical methods. In the in vivo part, OCAs were applied to the nail bed, and optical coherence tomography and optical digital capillaroscopy were used to evaluate their effects on optical clearing and capillary blood flow, respectively. In the in vitro part, the collected blood samples were incubated with the OCA and blood aggregation properties were estimated using diffuse light scattering techniques. The results indicate that OCAs significantly influence the optical properties of the nail bed and blood microrheology. These findings suggest that OCAs hold promise for improving optical imaging and diagnostics, particularly for nail bed applications, and can modify blood microrheology.

Optical clearing of human skin: Molecular modeling and in vivo OCT study

The results of in vivo immersion optical clearing of human skin under the action of two different optical clearing agents (OCAs), such as an aqueous sucrose solution and a radiographic contrast agent Omnipaque™ 300 (iohexol), were obtained with the use of optical coherence tomography (OCT) method. The rate of reduction of light scattering coefficient, obtained through an averaged A-scan of the OCT image in the region of dermis within the depths from 350 to 700 μm, were determined to evaluate the efficiency of optical clearing (EOC). The correlations between the EOC and the energy of intermolecular interaction of OCAs with a fragment of collagen peptide have been established as a result of molecular modeling by quantum chemistry methods HF/STO3G/DFT/B3LYP/6-311G(d) of a number of OCAs (glycerol, iohexol, sucrose, ribose, fructose, glucose) with mimetic peptide of collagen (GPH)3 .

Custom Hyperspectral Imaging System Reveals Unique Spectral Signatures of Heart, Kidney, and Liver Tissues

The rapid advancement of diagnostic and therapeutic optical techniques for oncology demands a good understanding of the optical properties of biological tissues. This study explores the capabilities of hyperspectral (HS) cameras as a non-invasive and non-contact optical imaging system to distinguish and highlight spectral differences inbiological soft tissuesof three structures (kidney, heart, and liver) for use inendoscopic interventionoropen surgery. The study presents an optical system consisting of two individual setups, the transmission setup, and the reflection setup, both incorporating anHS camerawith apolychromatic light sourcewithin the range of 380 to 1050 nm to measure tissue's light transmission (Tr) and diffuse light reflectance (Rd), respectively. The optical system was calibrated with a customizedliquid optical phantom, then 30 samples from various organs were investigated fortissue characterizationby measuring both Tr and Rd at the visible and near infrared (VIS-NIR) band. We exploited the ANOVA test, subsequently by a Tukey's test on the created three independent clusters (kidney vs. heart: group I / kidney vs. liver: group II / heart vs. liver: group III) to identify the optimum wavelength for each tissue regarding their spectroscopic optical properties in the VIS-NIR spectrum. The optimum spectral span for the determined light Tr of the three groups was 640 ∼ 680 nm, and the ideal range was 720 ∼ 760 nm for the measured light Rd for mutual group I and group II. However, the group III range was different at a range of 520 ∼ 560 nm. Therefore, the investigation provides vital information concerning theoptimum spectral scalefor the computed light Tr and Rd of the investigatedbiological tissues(kidney, liver, and heart) to be employed in diagnostic andtherapeutic medical applications.

Multimodal optical clearing to minimize light attenuation in biological tissues

The biggest obstacle to optical imaging is light attenuation in biological tissues. Conventional clearing techniques, such as agent-based clearing, improve light penetration depth by reducing scattering, but they are hampered by drawbacks including toxicity, low efficiency, slowness, and superficial performance, which prevent them from resolving the attenuation problem on their own. Therefore, quick, safe, and effective procedures have been developed. One of them involves using standing ultrasonic waves to build light waveguides that function effectively in the tissue depth while minimizing scattering. Temporal optical clearing is another agent-free strategy that we introduced in our previous article. Whereas not deep, this technique minimizes both light absorption and scattering by pulse width variation in ultra-short pulse regime. Consequently, it can be a complementary method for ultrasonic optical clearing. In this work, we enhanced the light penetration depth in chicken breast tissue by 10 times (0.67-6.7 cm), setting a record in literature by integrating three clearing methods: agent-based, ultrasound-based, and temporal. Here, optical coherence tomography, Bear-Lambert, and fluorescence tests have been used to study the light penetration depth and optical clearing efficiency. Presented work is an essential step in development of diagnostic techniques for human body, from cells to organs.

Multimodal Diagnostics of Changes in Rat Lungs after Vaping

(1) Background: The use of electronic cigarettes has become widespread in recent years. The use of e-cigarettes leads to milder pathological conditions compared to traditional cigarette smoking. Nevertheless, e-liquid vaping can cause morphological changes in lung tissue, which affects and impairs gas exchange. This work studied the changes in morphological and optical properties of lung tissue under the action of an e-liquid aerosol. To do this, we implemented the "passive smoking" model and created the specified concentration of aerosol of the glycerol/propylene glycol mixture in the chamber with the animal. (2) Methods: In ex vivo studies, the lungs of Wistar rats are placed in the e-liquid for 1 h. For in vivo studies, Wistar rats were exposed to the e-liquid vapor in an aerosol administration chamber. After that, lung tissue samples were examined ex vivo using optical coherence tomography (OCT) and spectrometry with an integrating sphere. Absorption and reduced scattering coefficients were estimated for the control and experimental groups. Histological sections were made according to the standard protocol, followed by hematoxylin and eosin staining. (3) Results: Exposure to e-liquid in ex vivo and aerosol in in vivo studies was found to result in the optical clearing of lung tissue. Histological examination of the lung samples showed areas of emphysematous expansion of the alveoli, thickening of the alveolar septa, and the phenomenon of plasma permeation, which is less pronounced in in vivo studies than for the exposure of e-liquid ex vivo. E-liquid aerosol application allows for an increased resolution and improved imaging of lung tissues using OCT. Spectral studies showed significant differences between the control group and the ex vivo group in the spectral range of water absorption. It can be associated with dehydration of lung tissue owing to the hyperosmotic properties of glycerol and propylene glycol, which are the main components of e-liquids. (4) Conclusions: A decrease in the volume of air in lung tissue and higher packing of its structure under e-liquid vaping causes a better contrast of OCT images compared to intact lung tissue.

Quantitative polarization-sensitive super-resolution solid immersion microscopy reveals biological tissues' birefringence in the terahertz range

Terahertz (THz) technology offers a variety of applications in label-free medical diagnosis and therapy, majority of which rely on the effective medium theory that assumes biological tissues to be optically isotropic and homogeneous at the scale posed by the THz wavelengths. Meanwhile, most recent research discovered mesoscale ([Formula: see text]) heterogeneities of tissues; [Formula: see text] is a wavelength. This posed a problem of studying the related scattering and polarization effects of THz-wave-tissue interactions, while there is still a lack of appropriate tools and instruments for such studies. To address this challenge, in this paper, quantitative polarization-sensitive reflection-mode THz solid immersion (SI) microscope is developed, that comprises a silicon hemisphere-based SI lens, metal-wire-grid polarizer and analyzer, a continuous-wave 0.6 THz ([Formula: see text] µm) backward-wave oscillator (BWO), and a Golay detector. It makes possible the study of local polarization-dependent THz response of mesoscale tissue elements with the resolution as high as [Formula: see text]. It is applied to retrieve the refractive index distributions over the freshly-excised rat brain for the two orthogonal linear polarizations of the THz beam, aimed at uncovering the THz birefringence (structural optical anisotropy) of tissues. The most pronounced birefringence is observed for the Corpus callosum, formed by well-oriented and densely-packed axons bridging the cerebral hemispheres. The observed results are verified by the THz pulsed spectroscopy of the porcine brain, which confirms higher refractive index of the Corpus callosum when the THz beam is polarized along axons. Our findings highlight a potential of the quantitative polarization THz microscopy in biophotonics and medical imaging.

Spotlight on Luminescence Thermometry: Basics, Challenges, and Cutting-Edge Applications

Luminescence (nano)thermometry is a remote sensing technique that relies on the temperature dependency of the luminescence features (e.g., bandshape, peak energy or intensity, and excited state lifetimes and risetimes) of a phosphor to measure temperature. This technique provides precise thermal readouts with superior spatial resolution in short acquisition times. Although luminescence thermometry is just starting to become a more mature subject, it exhibits enormous potential in several areas, e.g., optoelectronics, photonics, micro- and nanofluidics, and nanomedicine. This work reviews the latest trends in the field, including the establishment of a comprehensive theoretical background and standardized practices. The reliability, repeatability, and reproducibility of the technique are also discussed, along with the use of multiparametric analysis and artificial-intelligence algorithms to enhance thermal readouts. In addition, examples are provided to underscore the challenges that luminescence thermometry faces, alongside the need for a continuous search and design of new materials, experimental techniques, and analysis procedures to improve the competitiveness, accessibility, and popularity of the technology.

Photobiomodulation in dental extraction therapy: Postsurgical pain reduction and wound healing

BACKGROUND

This scoping review and analysis were designed to assess the amount of time spent delivering photobiomodulation (PBM) light therapy after dental extraction to improve postoperative pain and wound healing.

TYPES OF STUDIES REVIEWED

The scoping review was performed according to the Cochrane Collaboration and Preferred Reporting Items for Systematic Reviews and Meta-Analyses criteria. Publications were specific for human randomized controlled clinical trials, PBM after dental extraction therapy, and related clinical outcomes. Online databases searched included PubMed, Embase, Scopus, and Web of Science. Analyses were conducted to analyze the prescribed intervals of time (seconds) per application of PBM.

RESULTS

Of the 632 studies initially identified, 22 studies fulfilled the inclusion criteria. Postoperative pain and PBM were reported in 20 articles for 24 treatment groups, with treatment times ranging from 17 through 900 seconds and wavelengths from 550 through 1,064 nm. Clinical wound healing outcomes were reported in 6 articles for 7 groups with treatment times ranging from 30 through 120 seconds and wavelengths from 660 through 808 nm. PBM therapy was not associated with adverse events.

CONCLUSIONS AND PRACTICAL IMPLICATIONS

There is future potential to integrate PBM after dental extraction therapy to improve postoperative pain and clinical wound healing. The amount of time spent delivering PBM will vary by wavelength and the type of device. Further investigation is needed to translate PBM therapy into human clinical care.

Relevance and utility of the in-vivo and ex-vivo optical properties of the skin reported in the literature: a review [Invited]

Imaging non-invasively into the human body is currently limited by cost (MRI and CT scan), image resolution (ultrasound), exposure to ionising radiation (CT scan and X-ray), and the requirement for exogenous contrast agents (CT scan and PET scan). Optical imaging has the potential to overcome all these issues but is currently limited by imaging depth due to the scattering and absorption properties of human tissue. Skin is the first barrier encountered by light when imaging non-invasively, and therefore a clear understanding of the way that light interacts with skin is required for progress on optical medical imaging to be made. Here we present a thorough review of the optical properties of human skin measured in-vivo and compare these to the previously collated ex-vivo measurements. Both in-vivo and ex-vivo published data show high inter- and intra-publication variability making definitive answers regarding optical properties at given wavelengths challenging. Overall, variability is highest for ex-vivo absorption measurements with differences of up to 77-fold compared with 9.6-fold for the in-vivo absorption case. The impact of this variation on optical penetration depth and transport mean free path is presented and potential causes of these inconsistencies are discussed. We propose a set of experimental controls and reporting requirements for future measurements. We conclude that a robust in-vivo dataset, measured across a broad spectrum of wavelengths, is required for the development of future technologies that significantly increase the depth of optical imaging.

Transparent tissue in solid state for solvent-free and antifade 3D imaging

Optical clearing with high-refractive-index (high-n) reagents is essential for 3D tissue imaging. However, the current liquid-based clearing condition and dye environment suffer from solvent evaporation and photobleaching, causing difficulties in maintaining the tissue optical and fluorescent features. Here, using the Gladstone-Dale equation [(n-1)/density=constant] as a design concept, we develop a solid (solvent-free) high-n acrylamide-based copolymer to embed mouse and human tissues for clearing and imaging. In the solid state, the fluorescent dye-labeled tissue matrices are filled and packed with the high-n copolymer, minimizing scattering in in-depth imaging and dye fading. This transparent, liquid-free condition provides a friendly tissue and cellular environment to facilitate high/super-resolution 3D imaging, preservation, transfer, and sharing among laboratories to investigate the morphologies of interest in experimental and clinical conditions.

Hyperspectral assessment of acne skin exposed to intense pulsed light (IPL) intense pulsed light in acne treatment

BACKGROUND

The mechanism of intense pulsed light action on the skin is based on selective photothermolysis. The light delivered to the tissue is scattered and absorbed by chromophores that absorb a beam of radiation of a specific length. The skin reflectance changes depending on the physiological state of the tissue, as shown by the hyperspectral camera. The aim of the study was to assess the hyperspectral reflectance of acne skin before and after intense pulsed light (IPL) therapy and to compare it with the reflectance of healthy skin.

MATERIALS AND METHODS

The study involved 27 volunteers with diagnosed moderate acne. The control group consisted of 20 people without acne lesions. All acne volunteers underwent a series of four treatments using IPL at weekly intervals. The volunteers with acne lesions were photographed before the series of treatments and a week after the 4th treatment.

RESULTS

Acne skin shows lower reflectance than healthy skin. Acne skin after IPL therapy is characterized by a higher reflectance compared to acne skin before the therapy and resembles the reflectance of the skin of the control group. A statistically significant difference was found between the acne skin before the treatments and the skin of the control group.

CONCLUSIONS

The effect of IPL therapy on acne skin is the increase of its reflectance by reducing the number of chromophores, which brings it closer to the reflectance value of healthy skin. Hyperspectral imaging allows for: the evaluation of the treated skin at each stage, a precise selection of the light wavelength depending on the problem, and therefore, for optimizing the number of irradiations and increasing the safety of the therapy.

Spatio-Temporal Dynamics of Diffusion-Associated Deformations of Biological Tissues and Polyacrylamide Gels Observed with Optical Coherence Elastography

In this work, we use the method of optical coherence elastography (OCE) to enable quantitative, spatially resolved visualization of diffusion-associated deformations in the areas of maximum concentration gradients during diffusion of hyperosmotic substances in cartilaginous tissue and polyacrylamide gels. At high concentration gradients, alternating sign, near-surface deformations in porous moisture-saturated materials are observed in the first minutes of diffusion. For cartilage, the kinetics of osmotic deformations visualized by OCE, as well as the optical transmittance variations caused by the diffusion, were comparatively analyzed for several substances that are often used as optical clearing agents, i.e., glycerol, polypropylene, PEG-400 and iohexol, for which the effective diffusion coefficients were found to be 7.4 ± 1.8, 5.0 ± 0.8, 4.4 ± 0.8 and 4.6 ± 0.9 × 10^-6 cm²/s, respectively. For the osmotically induced shrinkage amplitude, the influence of the organic alcohol concentration appears to be more significant than the influence of its molecular weight. The rate and amplitude of osmotically induced shrinkage and dilatation in polyacrylamide gels is found to clearly depend on the degree of their crosslinking. The obtained results show that observation of osmotic strains with the developed OCE technique can be applied for structural characterization of a wide range of porous materials, including biopolymers. In addition, it may be promising for revealing alterations in the diffusivity/permeability of biological tissues that are potentially associated with various diseases.

Concentration-dependent photothermal conversion efficiency of gold nanoparticles under near-infrared laser and broadband irradiation

The photothermal conversion efficiency of gold different nanoparticles (GNPs) in different concentrations (1.25-20 µg/mL) and at different irradiation intensities of near-infrared (NIR) broadband and NIR laser irradiation is evaluated. Results show that for a concentration of 20.0 µg/mL, 40 nm gold nanospheres, 25 × 47 nm gold nanorods (GNRs), and 10 × 41 nm GNRs show a 4-110% higher photothermal conversion efficiency under NIR broadband irradiation than under NIR laser irradiation. Broadband irradiation seems suitable to attain higher efficiencies for the nanoparticles whose absorption wavelength is different from the irradiation wavelength. Lower concentrations (1.25-5 µg/mL) of such nanoparticles show 2-3 times higher efficiency under NIR broadband irradiation. For GNRs of sizes 10 × 38 nm and 10 × 41 nm, the different concentrations show almost equal efficiencies for NIR laser and broadband irradiation. On increasing the irradiation power from 0.3 to 0.5 W, for 10 × 41 nm GNRs in the concentration range of 2.5-20.0 µg/mL, NIR laser irradiation results in 5-32% higher efficiencies, while NIR broadband irradiation leads to a 6-11% increase in efficiency. Under NIR laser irradiation, the photothermal conversion efficiency increases with an increase in optical power. The findings will facilitate the selection of nanoparticle concentrations, irradiation source, and irradiation power for a variety of plasmonic photothermal applications.

Dynamic change in optical properties of a nanoparticle embedded tumor phantom for plasmonic photothermal cancer therapeutics

In this study, the temporal dynamic changes in optical properties of gold nanorods (GNR) embedded tumor phantom, during photothermal interaction, are reported for plasmonic photothermal therapeutics. Tumor mimicking bilayer phantoms were prepared by using 1% agarose incorporated with 0.1% coffee powder, 0.3% intralipid solution as epidermis layer; 3% intralipid solution and 0.3% human hemoglobin (Hb) powder as dermis layer. On incorporating GNRs of concentrations 10, 20, and 40 μg/ml within the phantom, the absorption coefficients increases 4-8 times, while there is minimal change in the reduced scattering coefficients. Further the absorption coefficient increased by ~8% with the incorporation of GNRs of concentration 40 μg/ml, while no considerable dynamic change in the optical properties is observed for the phantom embedded with GNRs of concentrations 10, and 20 μg/ml. The discussed results are useful for the selection of GNRs dose for pre-treatment planning of plasmonic photothermal cancer therapeutics.

Visualizing the Nucleome Using the CRISPR–Cas9 System: From in vitro to in vivo

One of the latest methods in modern molecular biology is labeling genomic loci in living cells using fluorescently labeled Cas protein. The NIH Foundation has made the mapping of the 4D nucleome (the three-dimensional nucleome on a timescale) a priority in the studies aimed to improve our understanding of chromatin organization. Fluorescent methods based on CRISPR-Cas are a significant step forward in visualization of genomic loci in living cells. This approach can be used for studying epigenetics, cell cycle, cellular response to external stimuli, rearrangements during malignant cell transformation, such as chromosomal translocations or damage, as well as for genome editing. In this review, we focused on the application of CRISPR-Cas fluorescence technologies as components of multimodal imaging methods for in vivo mapping of chromosomal loci, in particular, attribution of fluorescence signal to morphological and anatomical structures in a living organism. The review discusses the approaches to the highly sensitive, high-precision labeling of CRISPR-Cas components, delivery of genetically engineered constructs into cells and tissues, and promising methods for molecular imaging.

Measurement of tissue optical properties in a wide spectral range: a review [Invited]

A distinctive feature of this review is a critical analysis of methods and results of measurements of the optical properties of tissues in a wide spectral range from deep UV to terahertz waves. Much attention is paid to measurements of the refractive index of biological tissues and liquids, the knowledge of which is necessary for the effective application of many methods of optical imaging and diagnostics. The optical parameters of healthy and pathological tissues are presented, and the reasons for their differences are discussed, which is important for the discrimination of pathologies and the demarcation of their boundaries. When considering the interaction of terahertz radiation with tissues, the concept of an effective medium is discussed, and relaxation models of the effective optical properties of tissues are presented. Attention is drawn to the manifestation of the scattering properties of tissues in the THz range and the problems of measuring the optical properties of tissues in this range are discussed. In conclusion, a method for the dynamic analysis of the optical properties of tissues under optical clearing using an application of immersion agents is presented. The main mechanisms and technologies of optical clearing, as well as examples of the successful application for differentiation of healthy and pathological tissues, are analyzed.

Mouse model of selective cryolipolysis

BACKGROUND

Cryolipolysis is a noninvasive method of destroying adipocytes using controlled cooling, thereby enabling localized and targeted fat reduction. Due to their greater vulnerability to cold injury, adipocytes are selectively targeted, while other cell types are spared.

OBJECTIVES

This study aims to develop a mouse model of cryolipolysis to offer a reliable and convenient alternative to human models, providing a methodology to validate clinical hypotheses in-depth with relative ease, low cost, and efficiency. This further facilitates comprehensive studies of the molecular mechanisms involved in cryolipolysis.

MATERIALS AND METHODS

Mice (C57BL/6J) were placed under general anesthesia and were treated using our custom, miniaturized cryolipolysis system. A thermoelectric cooling probe was applied to the inguinal (ING) area for either a cold exposure of -10°C, or for a room temperature exposure for 10 minutes. The thickness of the subcutaneous fat of the mice was quantified using an optical coherence tomography (OCT) imaging system before and after the treatment. Histological analyses were performed before and after cryolipolysis at multiple time points.

RESULTS

OCT analysis showed that mice that underwent cold cryolipolysis treatment induced a significantly greater reduction of subcutaneous fat thickness 1 month after treatment than the control mice. The mice that received cold treatment had no skin injuries. The selective damage of adipocytes stimulated cold panniculitis that was characterized histologically by infiltration of immune cells 2 and 3 days after treatment.

CONCLUSION

This study shows that cryolipolysis performed in mice yields reproducible and measurable subcutaneous fat reduction, consistent with previous studies conducted in humans and pigs. Future studies can utilize the model of selective cryolipolysis developed by our group to further elucidate the cellular and molecular mechanisms of fat cell loss and improve clinical outcomes in humans.

Activation of Wnt/β-Catenin Signaling Involves 660 nm Laser Radiation on Epithelium and Modulates Lipid Metabolism

Research has proven that light treatment, specifically red light radiation, can provide more clinical benefits to human health. Our investigation was firstly conducted to characterize the tissue morphology of mouse breast post 660 nm laser radiation with low power and long-term exposure. RNA sequencing results revealed that light exposure with a higher intervention dosage could cause a number of differentially expressed genes compared with a low intervention dosage. Gene ontology analysis, protein–protein interaction network analysis, and gene set enrichment analysis results suggested that 660 nm light exposure can activate more transcription-related pathways in HC11 breast epithelial cells, and these pathways may involve modulating critical gene expression. To consider the critical role of the Wnt/T-catenin pathway in light-induced modulation, we hypothesized that this pathway might play a major role in response to 660 nm light exposure. To validate our hypothesis, we conducted qRT-PCR, immunofluorescence staining, and Western blot assays, and relative results corroborated that laser radiation could promote expression levels of β-catenin and relative phosphorylation. Significant changes in metabolites and pathway analysis revealed that 660 nm laser could affect nucleotide metabolism by regulating purine metabolism. These findings suggest that the Wnt/β-catenin pathway may be the major sensor for 660 nm laser radiation, and it may be helpful to rescue drawbacks or side effects of 660 nm light exposure through relative interventional agents.

Optical clearing and testing of lung tissue using inhalation aerosols: prospects for monitoring the action of viral infections

Optical clearing of the lung tissue aims to make it more transparent to light by minimizing light scattering, thus allowing reconstruction of the three-dimensional structure of the tissue with a much better resolution. This is of great importance for monitoring of viral infection impact on the alveolar structure of the tissue and oxygen transport. Optical clearing agents (OCAs) can provide not only lesser light scattering of tissue components but also may influence the molecular transport function of the alveolar membrane. Air-filled lungs present significant challenges for optical imaging including optical coherence tomography (OCT), confocal and two-photon microscopy, and Raman spectroscopy, because of the large refractive-index mismatch between alveoli walls and the enclosed air-filled region. During OCT imaging, the light is strongly backscattered at each air–tissue interface, such that image reconstruction is typically limited to a single alveolus. At the same time, the filling of these cavities with an OCA, to which water (physiological solution) can also be attributed since its refractive index is much higher than that of air will lead to much better tissue optical transmittance. This review presents general principles and advances in the field of tissue optical clearing (TOC) technology, OCA delivery mechanisms in lung tissue, studies of the impact of microbial and viral infections on tissue response, and antimicrobial and antiviral photodynamic therapies using methylene blue (MB) and indocyanine green (ICG) dyes as photosensitizers.

Optical Properties and Fluence Distribution in Rabbit Head Tissues at Selected Laser Wavelengths

The accurate estimation of skin and skull optical properties over a wide wavelength range of laser radiation has great importance in optogenetics and other related applications. In the present work, using the Kubelka-Munk model, finite-element solution of the diffusion equation, inverse adding-doubling (IAD), and Monte-Carlo simulation, we estimated the refractive index, absorption and scattering coefficients, penetration depth, and the optical fluence distribution in rabbit head tissues ex vivo, after dividing the heads into three types of tissues with an average thickness of skin of 1.1 mm, skull of 1 mm, and brain of 3 mm. The total diffuse reflectance and transmittance were measured using a single integrating sphere optical setup for laser radiation of 532, 660, 785, and 980 nm. The calculated optical properties were then applied to the diffusion equation to compute the optical fluence rate distribution at the boundary of the samples using the finite element method. Monte-Carlo simulation was implemented for estimating the optical fluence distribution through a model containing the three tissue layers. The scattering coefficient decreased at longer wavelengths, leading to an increase in optical fluence inside the tissue samples, indicating a higher penetration depth, especially at 980 nm. In general, the obtained results show good agreement with relevant literature.

Immersion optical clearing of adipose tissue in rats: ex vivo and in vivo studies

Optical clearing (OC) of adipose tissue has not been studied enough, although it can be promising in medical applications, including surgery and cosmetology, for example, to visualize blood vessels or increase the permeability of tissues to laser beams. The main objective of this work is to develop technology for OC of abdominal adipose tissue in vivo using hyperosmotic optical clearing agents (OCAs). The maximum OC effect (77%) was observed for ex vivo rat adipose tissue samples exposed to OCA on fructose basis for 90 minutes. For in vivo studies, the maximum effect of OC (65%) was observed when using OCA based on diatrizoic acid and dimethylsulfoxide for 120 minutes. Histological analysis showed that in vivo application of OCAs may induce a limited local necrosis of fat cells. The efficiency of OC correlated with local tissue damage through cell necrosis due to accompanied cell lipolysis.

MR and fluorescence imaging of gadobutrol-induced optical clearing of red fluorescent protein signal in an in vivo cancer model

Multimodality registration of optical and MR images in the same tissue volume in vivo may be enabled by MR contrast agents with an optical clearing (OC) effect. The goals of this study were to (a) investigate the effects of clinical MR contrast agent gadobutrol (GB) and its combinations as a potential OC agent assisting in fluorescence intensity (FI) imaging in vivo and (b) evaluate MRI as a tool for imaging of topical or systemic application of GB for the purpose of OC. Subcutaneous tumor xenografts expressing red fluorescent marker protein were used as disease models. MRI was performed at 1 T 1 H MRI using T1 -weighted 3D gradient-echo (T1w-3D GRE) sequences to measure time-dependent MR signal intensity changes by region of interest analysis after image segmentation. Topical application of 1.0 M or 0.7 M GB-containing OC mixture with water and dimethyl sulfoxide showed similar 30-40% increases of tumor FI during the initial 15 min. Afterwards, the OC effect of GB on FI and tumor/background FI ratio showed a decrease over time in the case of 1.0 M GB, unlike the 0.7 M GB mixture, which resulted in a steady increase of FI and tumor/background ratio for 15-60 min. The use of T1w-3D GRE MR pulse sequences showed that concentrated 1.0 M GB resulted in MR signal loss of the skin due to high magnetic susceptibility and that signal loss coincided with the OC effect. Intravenous injection of 0.3 mmol GB/kg resulted in a rapid but transient 40% increase of FI of the tumors. Overall, 1 T MRI enabled tracking of GB-containing OC compositions on the skin surface and tumor tissue, supporting the observation of a time-dependent FI increase in vivo.

Optical Clearing Agents for Optical Imaging Through Cartilage Tympanoplasties: A Preclinical Feasibility Study

HYPOTHESIS

Optical clearing agents (OCAs) can render cartilage tympanoplasty grafts sufficiently transparent to permit visualization of middle ear structures in an operated ear using optical coherence tomography (OCT) imaging.

METHODS

Pieces of human tragal cartilage were treated with glycerol, a commonly used OCA. A reference reflector was imaged with OCT through the tympanoplasty as it cleared and the optical attenuation of the graft was measured. The reversibility of clearing and the dimensional changes associated with glycerol absorption were also measured. In a separate experiment, a human cadaveric temporal bone was prepared to simulate an ossiculoplasty surgery with cartilage replacement of the tympanic membrane. A partial ossicular replacement prosthesis (PORP) inserted in the ear was imaged with OCT through a 0.4mm cartilage graft optically cleared with glycerol.

MAIN OUTCOME MEASURE

The optical attenuation of 0.4mm cartilage grafts decreased at 2.3+/-1.1 dB/min following treatment with glycerol, reaching a total decrease in attenuation of 13.6+/-5.9 dB after 7 minutes. The optical and dimensional effects of glycerol absorption were reversable following saline washout. In the temporal bone preparation, treatment of a cartilage graft with glycerol resulted in a 13 dB increase in signal-to-noise ratio and a 13 dB increase in contrast for visualizing the PORP through the graft with OCT.

CONCLUSIONS

Optical clearing agents offer a potential pathway towards optical coherence tomography imaging of the middle ear in post-surgical ears with cartilage grafts.

Normalization of optical fluence distribution for three-dimensional functional optoacoustic tomography of the breast

SIGNIFICANCE

In three-dimensional (3D) functional optoacoustic tomography (OAT), wavelength-dependent optical attenuation and nonuniform incident optical fluence limit imaging depth and field of view and can hinder accurate estimation of functional quantities, such as the vascular blood oxygenation. These limitations hinder OAT of large objects, such as a human female breast.

AIM

We aim to develop a measurement-data-driven method for normalization of the optical fluence distribution and to investigate blood vasculature detectability and accuracy for estimating vascular blood oxygenation.

APPROACH

The proposed method is based on reasonable assumptions regarding breast anatomy and optical properties. The nonuniform incident optical fluence is estimated based on the illumination geometry in the OAT system, and the depth-dependent optical attenuation is approximated using Beer-Lambert law.

RESULTS

Numerical studies demonstrated that the proposed method significantly enhanced blood vessel detectability and improved estimation accuracy of the vascular blood oxygenation from multiwavelength OAT measurements, compared with direct application of spectral linear unmixing without optical fluence compensation. Experimental results showed that the proposed method revealed previously invisible structures in regions deeper than 15 mm and/or near the chest wall.

CONCLUSIONS

The proposed method provides a straightforward and computationally inexpensive approximation of wavelength-dependent effective optical attenuation and, thus, enables mitigation of the spectral coloring effect in functional 3D OAT imaging.

In Silico, Combined Plasmonic Photothermal and Photodynamic Therapy in Mice

Plasmonic photothermal and photodynamic therapy (PPTT and PDT, respectively) are two cancer treatments that have the potential to be combined in a synergistic scheme. The aim of this study is to optimize the PPTT treatment part, in order to account for the PDT lack of coverage in the hypoxic tumor volume and in cancer areas laying in deep sites. For the needs of this study, a mouse was modeled, subjected to PDT and its necrotic area was estimated by using the MATLAB software. The same procedure was repeated for PPTT, using COMSOL Multiphysics. PPTT treatment parameters, namely laser power and irradiation time, were optimized in order to achieve the optimum therapeutic effect of the combined scheme. The PDT alone resulted in 54.8% tumor necrosis, covering the upper cancer layers. When the PPTT was also applied, the total necrosis percentage raised up to 99.3%, while all of the surrounding studied organs (skin, heart, lungs and trachea, ribs, liver and spleen) were spared. The optimized values of the PPTT parameters were 550 mW of laser power and 70 s of irradiation time. Hence, the PPTT–PDT combination shows great potential in achieving high levels of tumor necrosis while sparing the healthy tissues.

Optical Coherence Elastography as a Tool for Studying Deformations in Biomaterials: Spatially-Resolved Osmotic Strain Dynamics in Cartilaginous Samples

This paper presents a recently developed variant of phase-resolved Optical Coherence Elastography (OCE) enabling non-contact visualization of transient local strains of various origins in biological tissues and other materials. In this work, we demonstrate the possibilities of this new technique for studying dynamics of osmotically-induced strains in cartilaginous tissue impregnated with optical clearing agents (OCA). For poroelastic water-containing biological tissues, application of non-isotonic OCAs, various contrast additives, as well as drug solutions administration, may excite transient spatially-inhomogeneous strain fields of high magnitude in the tissue bulk, initiating mechanical and structural alterations. The range of the strain reliably observed by OCE varied from ±10⁻³ to ±0.4 for diluted and pure glycerol, correspondingly. The OCE-technique used made it possible to reveal previously inaccessible details of the complex spatio-temporal evolution of alternating-sign osmotic strains at the initial stages of agent diffusion. Qualitatively different effects produced by particular hydrophilic OCAs, such as glycerol and iohexol, are discussed, as well as concentration-dependent differences. Overall, the work demonstrates the unique abilities of the new OCE-modality in providing a deeper insight in real-time kinetics of osmotically-induced strains relevant to a broad range of biomedical applications.

Optical clearing of tissues: Issues of antimicrobial phototherapy and drug delivery

This review presents principles and novelties in the field of tissue optical clearing (TOC) technology, as well as application for optical monitoring of drug delivery and effective antimicrobial phototherapy. TOC is based on altering the optical properties of tissue through the introduction of immersion optical cleaning agents (OCA), which impregnate the tissue of interest. We also analyze various methods and kinetics of delivery of photodynamic agents, nanoantibiotics and their mixtures with OCAs into the tissue depth in the context of antimicrobial and antifungal phototherapy. In vitro and in vivo studies of antimicrobial phototherapies, such as photodynamic, photothermal plasmonic and photocatalytic, are summarized, and the prospects of a new TOC technology for effective killing of pathogens are discussed.

Detection of lipid efflux from foam cell models using a label-free infrared method

Synchrotron-based microFTIR spectroscopy was used to study the process of lipid efflux in a foam cell model. The anti-atherosclerotic drug, atorvastatin, removed low-density lipoprotein from the foam cells in a dose, and time dependent manner.

Assessment of tissue-specific changes in structure and function induced by in vivo skin/skull optical clearing techniques

BACKGROUND OBJECTIVES

Newly developed in vivo skin and skull optical clearing techniques can greatly improve the optical imaging performance, showing great advantages and clinical prospects. However, there is a poor understanding of in vivo optical clearing-induced changes in the skin and skull.

MATERIALS AND METHODS

Here, we employed in vivo skin/skull optical clearing techniques to improve the optical coherence tomography (OCT) imaging quality. And we also used polarization-sensitive OCT to monitor the dynamic changes in the polarization characteristics of the skin and skull during in vivo optical clearing processes. Two-photon imaging was used to evaluate changes in tissue barrier function and structure. Additionally, Raman spectra were employed for assessing the changes of each component in the skin and skull before and after optical clearing treatment.

RESULTS

The results indicated that the polarization states of the skin and skull were altered with the usages of optical clearing agents. And the barrier permeability and collagen fiber distribution of them became disordered. Furthermore, the Raman spectra of tissue demonstrated that the applications of in vivo tissue optical clearing methods could lead to the reduction of proteins, lipids, and inorganic salts in these two organs. Interestingly, after recovery treatment, the structure and function of the skin and skull could almost recover to the initial states.

CONCLUSION

In vivo tissue optical clearing can lead to changes in the structure and function of tissue, which was reversible to some extent. This study plays an important role in revealing the underlying mechanisms of tissue optical clearing techniques; moreover, it is conducive to the development and optimization of a novel in vivo tissue optical clearing approaches in future.

Light Technology for Efficient and Effective Photodynamic Therapy: A Critical Review

Photodynamic therapy (PDT) is a cancer treatment with strong potential over well-established standard therapies in certain cases. Non-ionising radiation, localisation, possible repeated treatments, and stimulation of immunological response are some of the main beneficial features of PDT. Despite the great potential, its application remains challenging. Limited light penetration depth, non-ideal photosensitisers, complex dosimetry, and complicated implementations in the clinic are some limiting factors hindering the extended use of PDT. To surpass actual technological paradigms, radically new sources, light-based devices, advanced photosensitisers, measurement devices, and innovative application strategies are under extensive investigation. The main aim of this review is to highlight the advantages/pitfalls, technical challenges and opportunities of PDT, with a focus on technologies for light activation of photosensitisers, such as light sources, delivery devices, and systems. In this vein, a broad overview of the current status of superficial, interstitial, and deep PDT modalities-and a critical review of light sources and their effects on the PDT process-are presented. Insight into the technical advancements and remaining challenges of optical sources and light devices is provided from a physical and bioengineering perspective.

Quo Vadis, Nanoparticle-Enabled In Vivo Fluorescence Imaging?

The exciting advancements that we are currently witnessing in terms of novel materials and synthesis approaches are leading to the development of colloidal nanoparticles (NPs) with increasingly greater tunable properties. We have now reached a point where it is possible to synthesize colloidal NPs with functionalities tailored to specific societal demands. The impact of this new wave of colloidal NPs has been especially important in the field of biomedicine. In that vein, luminescent NPs with improved brightness and near-infrared working capabilities have turned out to be optimal optical probes that are capable of fast and high-resolution in vivo imaging. However, luminescent NPs have thus far only reached a limited portion of their potential. Although we believe that the best is yet to come, the future might not be as bright as some of us think (and have hoped!). In particular, translation of NP-based fluorescence imaging from preclinical studies to clinics is not straightforward. In this Perspective, we provide a critical assessment and highlight promising research avenues based on the latest advances in the fields of luminescent NPs and imaging technologies. The disillusioned outlook we proffer herein might sound pessimistic at first, but we consider it necessary to avoid pursuing "pipe dreams" and redirect the efforts toward achievable-yet ambitious-goals.

Terahertz radiation and the skin: a review

SIGNIFICANCE

Terahertz (THz) radiation has demonstrated a great potential in biomedical applications over the past three decades, mainly due to its non-invasive and label-free nature. Among all biological specimens, skin tissue is an optimal sample for the application of THz-based methods because it allows for overcoming some intrinsic limitations of the technique, such as a small penetration depth (0.1 to 0.3 mm for the skin, on average).

AIM

We summarize the modern research results achieved when THz technology was applied to the skin, considering applications in both imaging/detection and treatment/modulation of the skin constituents.

APPROACH

We perform a review of literature and analyze the recent research achievements in THz applications for skin diagnosis and investigation.

RESULTS

The reviewed results demonstrate the possibilities of THz spectroscopy and imaging, both pulsed and continuous, for diagnosis of skin melanoma and non-melanoma cancer, dysplasia, scars, and diabetic condition, mainly based on the analysis of THz optical properties. The possibility of modulating cell activity and treatment of various diseases by THz-wave exposure is shown as well.

CONCLUSIONS

The rapid development of THz technologies and the obtained research results for skin tissue highlight the potential of THz waves as a research and therapeutic instrument. The perspectives on the use of THz radiation are related to both non-invasive diagnostics and stimulation and control of different processes in a living skin tissue for regeneration and cancer treatment.

Noninvasive Monitoring of Dynamical Processes in Bruised Human Skin Using Diffuse Reflectance Spectroscopy and Pulsed Photothermal Radiometry

We have augmented a recently introduced method for noninvasive analysis of skin structure and composition and applied it to monitoring of dynamical processes in traumatic bruises. The approach combines diffuse reflectance spectroscopy in visible spectral range and pulsed photothermal radiometry. Data from both techniques are analyzed simultaneously using a numerical model of light and heat transport in a four-layer model of human skin. Compared to the earlier presented approach, the newly introduced elements include two additional chromophores (β-carotene and bilirubin), individually adjusted thickness of the papillary dermal layer, and analysis of the bruised site using baseline values assessed from intact skin in its vicinity. Analyses of traumatic bruises in three volunteers over a period of 16 days clearly indicate a gradual, yet substantial increase of the dermal blood content and reduction of its oxygenation level in the first days after injury. This is followed by the emergence of bilirubin and relaxation of all model parameters towards the values characteristic for healthy skin approximately two weeks after the injury. The assessed parameter values and time dependences are consistent with existing literature. Thus, the presented methodology offers a viable approach for objective characterization of the bruise healing process.

Terahertz dielectric spectroscopy of human brain gliomas and intact tissues ex vivo: double-Debye and double-overdamped-oscillator models of dielectric response

Terahertz (THz) technology offers novel opportunities in the intraoperative neurodiagnosis. Recently, the significant progress was achieved in the study of brain gliomas and intact tissues, highlighting a potential for THz technology in the intraoperative delineation of tumor margins. However, a lack of physical models describing the THz dielectric permittivity of healthy and pathological brain tissues restrains the further progress in this field. In the present work, the ex vivo THz dielectric response of human brain tissues was analyzed using relaxation models of complex dielectric permittivity. Dielectric response of tissues was parametrized by a pair of the Debye relaxators and a pair of the overdamped-oscillators - namely, the double-Debye (DD) and double-overdamped-oscillator (DO) models. Both models accurately reproduce the experimental curves for the intact tissues and the WHO Grades I-IV gliomas. While the DD model is more common for THz biophotonics, the DO model is more physically rigorous, since it satisfies the sum rule. In this way, the DO model and the sum rule were, then, applied to estimate the content of water in intact tissues and gliomas ex vivo. The observed results agreed well with the earlier-reported data, justifying water as a main endogenous label of brain tumors in the THz range. The developed models can be used to describe completely the THz-wave - human brain tissues interactions in the frameworks of classical electrodynamics, being quite important for further research and developments in THz neurodiagnosis of tumors.

Pericapillary Edema Assessment by Means of the Nailfold Capillaroscopy and Laser Scanning Microscopy

Edema, i.e., fluid accumulation in the interstitial space, accompanies numerous pathological states of the human organism, including heart failure (HF), inflammatory response, and lymphedema. Nevertheless, techniques for quantitative assessment of the edema’s severity and dynamics are absent in clinical practice, and the analysis is mainly limited to physical examination. This fact stimulates the development of novel methods for fast and reliable diagnostics of fluid retention in tissues. In this work, we focused on the possibilities of two microscopic techniques, nailfold video capillaroscopy (NVC) and confocal laser scanning microscopy (CLSM), in the assessment of the short-term and long-term cutaneous edema. We showed that for the patients with HF, morphological parameters obtained by NVC—namely, the apical diameter of capillaries and the size of the perivascular zone—indicate long-term edema. On the other hand, for healthy volunteers, the application of two models of short-term edema, venous occlusion, and histamine treatment of the skin, did not reveal notable changes in the capillary parameters. However, a significant reduction of the NVC image sharpness was observed in this case, which was suggested to be due to water accumulation in the epidermis. To verify these findings, we made use of CLSM, which provides the skin structure with cellular resolution. It was observed that for the histamine-treated skin, the areas of the dermal papillae become hyporefractive, leading to the loss of contrast and the lower visibility of capillaries. Similar effect was observed for patients undergoing infusion therapy. Collectively, our results reveal the parameters can be used for pericapillary edema assessment using the NVC and CLSM, and paves the way for their application in a clinical set-up.

Optimal hyperosmotic agents for tissue immersion optical clearing in terahertz biophotonics

In this work, a thorough analysis of hyperosmotic agents for the immersion optical clearing (IOC) in terahertz (THz) range was performed. It was aimed at the selection of agents for the efficient enhancement of penetration depth of THz waves into biological tissues. Pulsed spectroscopy in the frequency range of 0.1 to 2.5 THz was applied for investigation of the optical properties of common IOC agents. Using the collimated transmission spectroscopy in visible range, binary diffusion coefficients of tissue water and agent in ex vivo rat brain tissue were measured. IOC agents were objectively compared using two-dimensional nomogram, accounting for their THz-wave absorption coefficients and binary diffusion coefficients. The results of this study demonstrate an interplay between the penetration depth enhancement and the diffusion rate and allow for pointing out glycerol as an optimal agent among the considered ones for particular applications in THz biophotonics.

Magnetic resonance contrast agents in optical clearing: Prospects for multimodal tissue imaging

Skin optical clearing effect ex vivo and in vivo was achieved by topical application of low molecular weight paramagnetic magnetic resonance contrast agents. This novel feature has not been explored before. By using collimated transmittance the diffusion coefficients of three clinically used magnetic resonance contrast agents, that is Gadovist, Magnevist and Dotarem as well as X-ray contrast agent Visipaque in mouse skin were determined ex vivo as (4.29 ± 0.39) × 10^-7 cm² /s, (5.00 ± 0.72) × 10^-7 cm² /s, (3.72 ± 0.67) × 10^-7 cm² /s and (1.64 ± 0.18) × 10^-7 cm² /s, respectively. The application of gadobutrol (Gadovist) resulted in efficient optical clearing that in general, was superior to other contrast agents tested and allowed to achieve: (a) more than 12-fold increase of transmittance over 10 minutes after application ex vivo; (b) markedly improved images of skin architecture obtained with optical coherence tomography; (c) an increase of the fluorescence intensity/background ratio in TagRFP-red fluorescent marker protein expressing tumor by five times after 15 minutes application into the skin in vivo. The obtained results have immediate implications for multimodality imaging because many contrast agents are capable of simultaneously enhancing the contrast of multiple imaging modalities.

Visualization of cortical cerebral blood flow dynamics during craniotomy in acute subdural hematoma using laser speckle imaging in a rat model

Mass evacuation with decompressive craniotomy is considered a standard intervention for acute subdural hematoma (ASDH). However, hemispheric swelling complicates the intraoperative and postoperative management of ASDH patients, and previous studies have revealed that this approach can damage ischemic/reperfusion (I/R) injury. Few studies have focused on the cerebrovascular response following traumatic brain injury (TBI). To characterize the relative cerebral blood flow (rCBF) before and after removal of the hematoma, rats were injured by a subdural infusion of 400 μL of venous blood or paraffin oil. MRI scans were performed. Then, we monitored cortical rCBF during hematoma removal in real time using laser speckle imaging (LSCI) in ASDH rats. The CBF of arteriovenous and capillary regions were quantified and normalized to their own baseline values via a custom algorithm. In the sham group, the cortical CBF was higher post-craniotomy than pre-craniotomy. However, in the hematoma injection group, the CBF of arteries and capillaries was higher while the venous CBF was lower post-craniotomy than pre-craniotomy. The difference in the changes in vein CBF that occurred between the two groups was statistically significant. The three components of the vascular system showed heterogeneous responses to craniotomy, which may be the basis for secondary brain injury.

In vivo detection of human cutaneous beta-carotene using computational optical clearing

The content of dermal beta-carotene can be a good indicator showing the body health. Because, it is involved in production of vitamin A maintaining healthy skin and mucous membranes. Also, it reduces the risk of cardiovascular diseases and its antioxidant capacity prevents the formation of cancerous cells. In this work, we use Raman spectroscopy and a low-cost diffuse reflectance spectroscopy (DRS) to detect the dermal beta-carotene spectra. We apply computational optical clearing (OC) method to in vivo evaluation the concentration of this chromophore. The results show that Raman spectroscopy is a good tool for in vitro detection of carotenoids but is not able to clearly discriminate the individual carotenoids in skin tissue in vivo. The results also show that using OC enhances the ability of low-cost diffuse reflection spectroscopy for in vivo detection of dermal beta-carotene in humans. This method can be used as a low-cost and portable device to screening the concentration of chromophores such as melanin and carotenoid molecules for oncological studies.

Biomedical Applications of Tissue Clearing and Three-Dimensional Imaging in Health and Disease

Three-dimensional (3D) optical imaging techniques can expand our knowledge about physiological and pathological processes that cannot be fully understood with 2D approaches. Standard diagnostic tests frequently are not sufficient to unequivocally determine the presence of a pathological condition. Whole-organ optical imaging requires tissue transparency, which can be achieved by using tissue clearing procedures enabling deeper image acquisition and therefore making possible the analysis of large-scale biological tissue samples. Here, we review currently available clearing agents, methods, and their application in imaging of physiological or pathological conditions in different animal and human organs. We also compare different optical tissue clearing methods discussing their advantages and disadvantages and review the use of different 3D imaging techniques for the visualization and image acquisition of cleared tissues. The use of optical tissue clearing resources for large-scale biological tissues 3D imaging paves the way for future applications in translational and clinical research.

Whole-Brain Profiling of Cells and Circuits in Mammals by Tissue Clearing and Light-Sheet Microscopy

Tissue clearing and light-sheet microscopy have a 100-year-plus history, yet these fields have been combined only recently to facilitate novel experiments and measurements in neuroscience. Since tissue-clearing methods were first combined with modernized light-sheet microscopy a decade ago, the performance of both technologies has rapidly improved, broadening their applications. Here, we review the state of the art of tissue-clearing methods and light-sheet microscopy and discuss applications of these techniques in profiling cells and circuits in mice. We examine outstanding challenges and future opportunities for expanding these techniques to achieve brain-wide profiling of cells and circuits in primates and humans. Such integration will help provide a systems-level understanding of the physiology and pathology of our central nervous system.

Optimized skin optical clearing for optical coherence tomography monitoring of encapsulated drug delivery through the hair follicles

Hair follicles (HF) represent a drug delivery reservoir for improved treatment of skin disorders. Although various particulate systems play an important role in HF-targeting, their optical monitoring in skin is challenging due to strong light scattering. Optical clearing is an effective approach allowing the increasing of particle detection depth in skin. The enhancement of optical probing depth (OPD) and optical detection depth (ODD) of particle localization using optical coherence tomography (OCT) was evaluated under application of various optical clearing agents (OCAs) together with skin permeability enhancers ex vivo in rats. Efficient OPD increasing was demonstrated for all investigated OCAs. However, skin dehydration under action of hyperosmotic agents led to the worsening of OCT-contrast in dermis decreasing the ODD. Lipophilic agents provided optical clearing of epidermis without its dehydration. The highest ODD was obtained at application of a PEG-400/oleic acid mixture. This OCA was tested in vivo showing beneficial ODD and OPD enhancement.

Moving tissue spectral window to the deep-ultraviolet via optical clearing

The optical immersion clearing technique has been successfully applied through the last 30 years in the visible to near infrared spectral range, and has proven to be a promising method to promote the application of optical technologies in clinical practice. To investigate its potential in the ultraviolet range, collimated transmittance spectra from 200 to 1000 nm were measured from colorectal muscle samples under treatment with glycerol-water solutions. The treatments created two new optical windows with transmittance efficiency peaks at 230 and 300 nm, with magnitude increasing with glycerol concentration in the treating solution. Such discovery opens the opportunity to develop clinical procedures to perform diagnosis or treatments in the ultraviolet.

Detecting Retinal Nerve Fibre Layer Segmentation Errors on Spectral Domain-Optical Coherence Tomography with a Deep Learning Algorithm

In this study we developed a deep learning (DL) algorithm that detects errors in retinal never fibre layer (RNFL) segmentation on spectral-domain optical coherence tomography (SDOCT) B-scans using human grades as the reference standard. A dataset of 25,250 SDOCT B-scans reviewed for segmentation errors by human graders was randomly divided into validation plus training (50%) and test (50%) sets. The performance of the DL algorithm was evaluated in the test sample by outputting a probability of having a segmentation error for each B-scan. The ability of the algorithm to detect segmentation errors was evaluated with the area under the receiver operating characteristic (ROC) curve. Mean DL probabilities of segmentation error in the test sample were 0.90 ± 0.17 vs. 0.12 ± 0.22 (P < 0.001) for scans with and without segmentation errors, respectively. The DL algorithm had an area under the ROC curve of 0.979 (95% CI: 0.974 to 0.984) and an overall accuracy of 92.4%. For the B-scans with severe segmentation errors in the test sample, the DL algorithm was 98.9% sensitive. This algorithm can help clinicians and researchers review images for artifacts in SDOCT tests in a timely manner and avoid inaccurate diagnostic interpretations.

Enhanced near infrared optical access to the brain with a transparent cranial implant and scalp optical clearing

We report on the enhanced optical transmittance in the NIR wavelength range (900 to 2400 nm) offered by a transparent Yttria-stabilized zirconia (YSZ) implant coupled with optical clearing agents (OCAs). The enhancement in optical access to the brain is evaluated upon comparing ex-vivo transmittance measurements of mice native skull and the YSZ cranial implant with scalp and OCAs. An increase in transmittance of up to 50% and attenuation lengths of up to 2.4 mm (i.e., a five-fold increase in light penetration) are obtained with the YSZ implant and the OCAs. The use of this ceramic implant and the biocompatible optical clearing agents offer attractive features for NIR optical techniques for brain theranostics.