Controling the scattering of intralipid by using optical clearing agents

A robust vessel-labeling pipeline with high tissue clearing compatibility for 3D mapping of vascular networks

The combination of vessel-labeling, tissue-clearing, and light-sheet imaging techniques provides a potent tool for accurately mapping vascular networks, enabling the assessment of vascular remodeling in vascular-related disorders. However, most vascular labeling methods face challenges such as inadequate labeling efficiency or poor compatibility with current tissue clearing technology, which significantly undermines the image quality. To address this limitation, we introduce a vessel-labeling pipeline, termed Ultralabel, which relies on a specially designed dye hydrogel containing lysine-fixable dextran and gelatins for double enhancement. Ultralabel demonstrates not only excellent vessel-labeling capability but also strong compatibility with all tissue clearing methods tested, which outperforms other vessel-labeling methods. Consequently, Ultralabel enables fine mapping of vascular networks in diverse organs, as well as multi-color labeling alongside other labeling techniques. Ultralabel should provide a robust and user-friendly method for obtaining 3D vascular networks in different biomedical applications.

Model equations of light scattering properties and a characteristic time of light propagation for polydisperse colloidal suspensions at different volume fractions

We developed model equations of light scattering properties and a characteristic time of light propagation for polydisperse colloidal suspensions at different volume fractions. By the model equations, we examined numerical results using the first-order (dependent) scattering theory (FST) and radiative transfer theory in 600-980 nm wavelength. The model equations efficiently treat the interference of electric fields scattered from colloidal particles by a single effective coefficient, providing fast computation. Meanwhile, the FST provides accurate but complicated treatment. We found the interference effects on the scattering properties and characteristic time depend linearly on wavelength. Dimensionless analysis showed a simple mechanism of the interference effects, independently of wavelength and source-detector distance.

Impact of optical clearing on ex vivo human skin optical properties characterized by spatially resolved multimodal spectroscopy

A spatially resolved multimodal spectroscopic device was used on a two-layered "hybrid" model made of ex vivo skin and fluorescent gel to investigate the effect of skin optical clearing on the depth sensitivity of optical spectroscopy. Time kinetics of fluorescence and diffuse reflectance spectra were acquired in four experimental conditions: with optical clearing agent (OCA) 1 made of polyethylene glycol 400 (PEG-400), propylene glycol and sucrose; with OCA 2 made of PEG-400 and dimethyl sulfoxide (DMSO); with saline solution as control and a "dry" condition. An increase in the gel fluorescence back reflected intensity was measured after optical clearing. Effect of OCA 2 turned out to be stronger than that of OCA 1, possibly due to DMSO impact on the stratum corneum keratin conformation. Complementary experimental results showed increased light transmittance through the skin and confirmed that the improvement in the depth sensitivity of the multimodal spectroscopic approach is related not only to the dehydration and refractive indices matching due to optical clearing, but also to the mechanical compression of tissues caused by the application of the spectroscopic probe.

Deep convolutional neural network-based scatterer density and resolution estimators in optical coherence tomography

We present deep convolutional neural network (DCNN)-based estimators of the tissue scatterer density (SD), lateral and axial resolutions, signal-to-noise ratio (SNR), and effective number of scatterers (ENS, the number of scatterers within a resolution volume). The estimators analyze the speckle pattern of an optical coherence tomography (OCT) image in estimating these parameters. The DCNN is trained by a large number (1,280,000) of image patches that are fully numerically generated in OCT imaging simulation. Numerical and experimental validations were performed. The numerical validation shows good estimation accuracy as the root mean square errors were 0.23%, 3.65%, 3.58%, 3.79%, and 6.15% for SD, lateral and axial resolutions, SNR, and ENS, respectively. The experimental validation using scattering phantoms (Intralipid emulsion) shows reasonable estimations. Namely, the estimated SDs were proportional to the Intralipid concentrations, and the average estimation errors of lateral and axial resolutions were 1.36% and 0.68%, respectively. The scatterer density estimator was also applied to an in vitro tumor cell spheroid, and a reduction in the scatterer density during cell necrosis was found.

Tissue Optical Clearing for Biomedical Imaging: From In Vitro to In Vivo

Tissue optical clearing technique provides a prospective solution for the application of advanced optical methods in life sciences. This chapter firstly gives a brief introduction to mechanisms of tissue optical clearing techniques, from the physical mechanism to chemical mechanism, which is the most important foundation to develop tissue optical clearing methods. During the past years, in vitro and in vivo tissue optical clearing methods were developed. In vitro tissue optical clearing techniques, including the solvent-based clearing methods and the hydrophilic reagents-based clearing methods, combined with labeling technique and advanced microscopy, can be applied to image 3D microstructure of tissue blocks or whole organs such as brain and spinal cord with high resolution. In vivo skin or skull optical clearing, promise various optical imaging techniques to detect cutaneous or cortical cell and vascular structure and function without surgical window.

Physical and chemical mechanisms of tissue optical clearing

Advanced optical methods combined with various probes pave the way toward molecular imaging within living cells. However, major challenges are associated with the need to enhance the imaging resolution even further to the subcellular level for the imaging of larger tissues, as well as for in vivo studies. High scattering and absorption of opaque tissues limit the penetration of light into deep tissues and thus the optical imaging depth. Tissue optical clearing technique provides an innovative way to perform deep-tissue imaging. Recently, various optical clearing methods have been developed, which provide tissue clearing based on similar physical principles via different chemical approaches. Here, we introduce the mechanisms of the current clearing methods from fundamental physical and chemical perspectives, including the main physical principle, refractive index matching via various chemical approaches, such as dissociation of collagen, delipidation, decalcification, dehydration, and hyperhydration, to reduce scattering, as well as decolorization to reduce absorption.

Urea-based amino sugar agent clears murine liver and preserves protein fluorescence and lipophilic dyes

Five established clearing protocols were compared with a modified and simplified method to determine an optimal clearing reagent for three-dimensionally visualizing fluorophores in the murine liver, a challenging organ to clear. We report successful clearing of whole liver lobes by modification of an established protocol (UbasM) using only Ub-1, a urea-based amino sugar reagent, in a simpler protocol that requires only a 24-h processing time. With Ub-1 alone, we observed sufficiently preserved liver tissue structure in three dimensions along with excellent preservation of fluorophore emissions from endogenous protein reporters and lipophilic tracer dyes. This streamlined technique can be used for 3D cell lineage tracing and fluoroprobe-based reporter gene expression to compare various experimental conditions.

This study presents a simplified protocol for optically clearing murine liver tissue in only 24 h using one simple urea-based amino sugar solution and a single incubation. This method preserves fluorescence of transgenically expressed proteins and lipophilic tracer dyes within the context of native spatial morphology.

Improving the characterization of ex vivo human brain optical properties using high numerical aperture optical coherence tomography by spatially constraining the confocal parameters

Significance: The optical properties of biological samples provide information about the structural characteristics of the tissue and any changes arising from pathological conditions. Optical coherence tomography (OCT) has proven to be capable of extracting tissue's optical properties using a model that combines the exponential decay due to tissue scattering and the axial point spread function that arises from the confocal nature of the detection system, particularly for higher numerical aperture (NA) measurements. A weakness in estimating the optical properties is the inter-parameter cross-talk between tissue scattering and the confocal parameters defined by the Rayleigh range and the focus depth. Aim: In this study, we develop a systematic method to improve the characterization of optical properties with high-NA OCT. Approach: We developed a method that spatially parameterizes the confocal parameters in a previously established model for estimating the optical properties from the depth profiles of high-NA OCT. Results: The proposed parametrization model was first evaluated on a set of intralipid phantoms and then validated using a low-NA objective in which cross-talk from the confocal parameters is negligible. We then utilize our spatially parameterized model to characterize optical property changes introduced by a tissue index matching process using a simple immersion agent, 2,2'-thiodiethonal. Conclusions: Our approach improves the confidence of parameter estimation by reducing the degrees of freedom in the non-linear fitting model.

Penetration-enhanced optical coherence tomography angiography with optical clearing agent for clinical evaluation of human skin

BACKGROUND

Optical coherence tomography angiography (OCTA) is an emerging imaging technique which shows its advantages over visualizing microcirculation with free label. However, its shortcomings in imaging depth limit its development in dermatological field. Nowadays, the newly optical clearing agent (OCA) designed for skin optical imaging demonstrates its potential. In our study, whether this OCA can improve the imaging ability of OCTA in healthy human skin and whether the combination of them is beneficial to compare the lesions and the contralateral normal skins in the patients with port wine stains (PWS) have been investigated.

METHODS

Five healthy volunteers and 3 PWS patients were recruited in this study. In terms of healthy people, the opisthenar area which has same structure information as facial skin was taken for investigating the OCA's ability of enhancing OCTA imaging depth on healthy human skin, besides, in order to verifying whether the exists of skin corneum interfere OCA's function, we compared the effect of only using OCA with that of comprehensive using pre-processing skin and OCA. There are one physical removing corneum method by using medical tape to strip opisthenar skin for over 20-time and one chemical way through applying exfoliating cream. For PWS patient, the combining using OCA and OCTA was applied at the lesion area and the contralateral normal area for the purpose of verifying their ability to provide the information of vessels.

RESULTS

This novel OCA had excellent efficacy to increase the penetration depth of human opisthenar skin for the OCTA imaging by approximately 0.16 ± 0.03 mm. Pre-processing of stratum corneum with an exfoliating cream or medical tape stripping did not further benefit the penetrating efficacy of the OCA. Moreover, according to a comprehensive analysis of the OCTA images enhanced by the OCA, the PWS lesions usually have larger density and diameter of the vessels which located in deep layers (beyond 0.21 mm) than the contralateral normal skin.

CONCLUSIONS

The OCTA imaging depth and contrast were significantly improved by the OCA. The OCA application is a simple and efficient clinical procedure for OCTA enhancement. Moreover, it demonstrated great clinical value to compare the normal skin and the PWS lesions in the patients by the enhanced OCTA imaging.

Normalized field autocorrelation function-based optical coherence tomography three-dimensional angiography

Optical coherence tomography angiography (OCTA) has been widely used for en face visualization of the microvasculature, but is challenged for real three-dimensional (3-D) topologic imaging due to the "tail" artifacts that appear below large vessels. Further, OCTA is generally incapable of differentiating descending arterioles from ascending venules. We introduce a normalized field autocorrelation function-based OCTA (g1-OCTA), which minimizes the tail artifacts and is capable of distinguishing penetrating arterioles from venules in the 3-D image. g1   (  τ  )   is calculated from repeated optical coherence tomography (OCT) acquisitions for each spatial location. The decay amplitude of g1   (  τ  )   is retrieved to represent the dynamics for each voxel. To account for the small g1   (  τ  )   decay in capillaries where red blood cells are flowing slowly and discontinuously, Intralipid is injected to enhance the OCT signal. We demonstrate that the proposed technique realizes 3-D OCTA with negligible tail projections and the penetrating arteries are readily identified. In addition, compared to regular OCTA, the proposed g1-OCTA largely increased the depth-of-field. This technique provides a more accurate rendering of the vascular 3-D anatomy and has the potential for more quantitative characterization of vascular networks.

Quantitative assessment of optical clearing methods in various intact mouse organs

Various tissue optical clearing techniques have sprung up for large volume imaging. However, there are few methods showed clearing and imaging data on different organs while most of them were focused on mouse brain, and as a result, it is difficult to select the suitable method for organs in practical applications due to lack of quantitative evaluation and comprehensive comparison. Therefore, it is necessary to evaluate and compare the performances of clearing methods for different organs. In this paper, several typical optical clearing methods were applied, including 3DISCO, uDISCO, SeeDB, FRUIT, CUBIC, ScaleS and PACT to clear intact brain, heart, kidney, liver, spleen, stomach, lung, small intestine, skin and muscle. The clearing efficiency, sample deformation, fluorescence preservation and imaging depth of these methods were quantitatively evaluated. Finally, based on the systemic evaluation of various parameters described above, the appropriate clearing method for specific organ including kidney or intestine was screened out. This paper will provide important references for selection of appropriate clearing methods in related researches.

Optical clearing for multiscale biological tissues

Three-dimensional reconstruction of tissue structures is essential for biomedical research. The development of light microscopes and various fluorescent labeling techniques provides powerful tools for this motivation. However, optical imaging depth suffers from strong light scattering due to inherent heterogeneity of biological tissues. Tissue optical clearing technology provides a distinct solution and permits us to image large volumes with high resolution. Until now, various clearing methods have been developed. In this study, from the perspective of the end users, we review in vitro tissue optical clearing techniques based on the sample features in terms of size and age, enumerate the methods suitable for immunostaining and lipophilic dyes and summarize the combinations with various imaging techniques. We hope this review will be helpful for researchers to choose the most suitable clearing method from a variety of protocols to meet their specific needs.

Elevated-temperature-induced acceleration of PACT clearing process of mouse brain tissue

Tissue optical clearing technique shows a great potential for neural imaging with high resolution, especially for connectomics in brain. The passive clarity technique (PACT) is a relative simple clearing method based on incubation, which has a great advantage on tissue transparency, fluorescence preservation and immunostaining compatibility for imaging tissue blocks. However, this method suffers from long processing time. Previous studies indicated that increasing temperature can speed up the clearing. In this work, we aim to systematacially and quantitatively study this influence based on PACT with graded increase of temperatures. We investigated the process of optical clearing of brain tissue block at different temperatures, and found that elevated temperature could accelerate the clearing process and also had influence on the fluorescence intensity. By balancing the advantages with drawbacks, we conclude that 42-47 °C is an alternative temperature range for PACT, which can not only produce faster clearing process, but also retain the original advantages of PACT by preserving endogenous fluorescence well, achieving fine morphology maintenance and immunostaining compatibility.

Collaborative effects of wavefront shaping and optical clearing agent in optical coherence tomography

We demonstrate that simultaneous application of optical clearing agents (OCAs) and complex wavefront shaping in optical coherence tomography (OCT) can provide significant enhancement of penetration depth and imaging quality. OCA reduces optical inhomogeneity of a highly scattering sample, and the wavefront shaping of illumination light controls multiple scattering, resulting in an enhancement of the penetration depth and signal-to-noise ratio. A tissue phantom study shows that concurrent applications of OCA and wavefront shaping successfully operate in OCT imaging. The penetration depth enhancement is further demonstrated for <italic<ex vivo</italic< mouse ears, revealing hidden structures inaccessible with conventional OCT imaging.

Study of the inhibition effect of thiazone on muscle optical clearing

We investigated the effect of thiazone, a widely used penetration enhancer, on in vitro porcine skin and muscle tissue by single-integrating sphere technique during optical clearing (OC) treatment. The results showed that thiazone induced an increase on the total transmittance of skin which led to a reduction in that of muscle in the spectral range from 400 to 800 nm. Small particles crystalized out from the thiazone-treated muscle were observed by microscopy imaging. With the help of x-ray diffraction measurement, we ascertained that the crystal was a single-crystal of thiazone, which mainly induced an increase of the scattering. Contrast transmittance measurements carried on the mixture of water, thizaone–propylene glycol solution showed that the free water in muscle could be the main reason for the thiazone crystallization. Therefore, during OC treatment of thiazone, the remarkable effect on skin and the noticeable inhibition effect on subcutaneous muscle tissue after penetrating into the skin should be considered. The experimental results provide such a reference for the choice of penetration enhancer.

Dynamic contrast optical coherence tomography images transit time and quantifies microvascular plasma volume and flow in the retina and choriocapillaris

Despite the prevalence of optical imaging techniques to measure hemodynamics in large retinal vessels, quantitative measurements of retinal capillary and choroidal hemodynamics have traditionally been challenging. Here, a new imaging technique called dynamic contrast optical coherence tomography (DyC-OCT) is applied in the rat eye to study microvascular blood flow in individual retinal and choroidal layers in vivo. DyC-OCT is based on imaging the transit of an intravascular tracer dynamically as it passes through the field-of-view. Hemodynamic parameters can be determined through quantitative analysis of tracer kinetics. In addition to enabling depth-resolved transit time, volume, and flow measurements, the injected tracer also enhances OCT angiograms and enables clear visualization of the choriocapillaris, particularly when combined with a post-processing method for vessel enhancement. DyC-OCT complements conventional OCT angiography through quantification of tracer dynamics, similar to fluorescence angiography, but with the important added benefit of laminar resolution.

Rapid and prodium iodide-compatible optical clearing method for brain tissue based on sugar/sugar-alcohol

The developed optical clearing methods show great potential for imaging of large-volume tissues, but these methods present some nonnegligible limitations such as complexity of implementation and long incubation times. In this study, we tried to screen out rapid optical clearing agents by means of molecular dynamical simulation and experimental demonstration. According to the optical clearing potential of sugar and sugar-alcohol,we further evaluated the improvement in the optical clearing efficacy of mouse brain samples, imaging depth, fluorescence preservation, and linear deformation. The results showed that drops of sorbitol, sucrose, and fructose could quickly make the mouse brain sample transparent within 1 to 2 min, and induce about threefold enhancement in imaging depth. The former two could evidently enhance the fluorescence intensity of green fluorescent protein (GFP) and prodium iodide (PI) nuclear dye. Fructose could significantly increase the fluorescence intensity of PI, but slightly decrease the fluorescence intensity of GFP. Even though the three agents caused some shrinkage in samples, the contraction in horizontal and longitudinal directions are almost the same.

Optical clearing of skin enhanced with hyaluronic acid for increased contrast of optoacoustic imaging

Enhanced delivery of optical clearing agents (OCA) through skin may improve sensitivity of optical and optoacoustic (OA) methods of imaging, sensing, and monitoring. This report describes a two-step method for enhancement of light penetration through skin. Here, we demonstrate that topical application of hyaluronic acid (HA) improves skin penetration of hydrophilic and lipophilic OCA and thus enhances their performance. We examined the OC effect of 100% polyethylene and polypropylene glycols (PPGs) and their mixture after pretreatment by HA, and demonstrated significant increase in efficiency of light penetration through skin. Increased light transmission resulted in a significant increase of OA image contrast in vitro. Topical pretreatment of skin for about 30 min with 0.5% HA in aqueous solution offers effective delivery of low molecular weight OCA such as a mixture of PPG-425 and polyethylene glycol (PEG)-400. The developed approach of pretreatment by HA prior to application of clearing agents (PEG and PPG) resulted in a ∼ 47-fold increase in transmission of red and near-infrared light and significantly enhanced contrast of OA images.

Laminar microvascular transit time distribution in the mouse somatosensory cortex revealed by Dynamic Contrast Optical Coherence Tomography

The transit time distribution of blood through the cerebral microvasculature both constrains oxygen delivery and governs the kinetics of neuroimaging signals such as blood-oxygen-level-dependent functional Magnetic Resonance Imaging (BOLD fMRI). However, in spite of its importance, capillary transit time distribution has been challenging to quantify comprehensively and efficiently at the microscopic level. Here, we introduce a method, called Dynamic Contrast Optical Coherence Tomography (DyC-OCT), based on dynamic cross-sectional OCT imaging of an intravascular tracer as it passes through the field-of-view. Quantitative transit time metrics are derived from temporal analysis of the dynamic scattering signal, closely related to tracer concentration. Since DyC-OCT does not require calibration of the optical focus, quantitative accuracy is achieved even deep in highly scattering brain tissue where the focal spot degrades. After direct validation of DyC-OCT against dilution curves measured using a fluorescent plasma label in surface pial vessels, we used DyC-OCT to investigate the transit time distribution in microvasculature across the entire depth of the mouse somatosensory cortex. Laminar trends were identified, with earlier transit times and less heterogeneity in the middle cortical layers. The early transit times in the middle cortical layers may explain, at least in part, the early BOLD fMRI onset times observed in these layers. The layer-dependencies in heterogeneity may help explain how a single vascular supply manages to deliver oxygen to individual cortical layers with diverse metabolic needs.

Surface layering properties of Intralipid phantoms

Intralipid has become an extensively studied and widely used reference and calibration phantom for diffuse optical imaging technologies. In this study we call attention to the layering properties of Intralipid emulsions, which are commonly assumed to have homogeneous optical properties. By measurement of spatial frequency domain reflectance in combination with an analytical solution of the radiative transfer equation for two-layered media, we make quantitative investigations on the formation of a surface layer on different dilutions of Intralipid. Our findings are verified by an independent spatially resolved reflectance setup giving evidence of a time dependent, thin and highly scattering surface layer on top of Intralipid-water emulsions. This layer should be considered when using Intralipid as an optical calibration or reference phantom.

Flexible tool for simulating the bulk optical properties of polydisperse spherical particles in an absorbing host: experimental validation

In this study, a flexible tool to simulate the bulk optical properties of polydisperse spherical particles in an absorbing host medium is described. The generalized Mie solution for Maxwell's equations is consulted to simulate the optical properties for a spherical particle in an absorbing host, while polydispersity of the particle systems is supported by discretization of the provided particle size distributions. The number of intervals is optimized automatically in an efficient iterative procedure. The developed tool is validated by simulating the bulk optical properties for two aqueous nanoparticle systems and an oil-in-water emulsion in the visible and near-infrared wavelength range, taking into account the representative particle sizes and refractive indices. The simulated bulk optical properties matched closely (R2 ≥ 0.899) with those obtained by reference measurements.

Dependent scattering in Intralipid® phantoms in the 600-1850 nm range

The effect of dependent scattering on the bulk scattering properties of intralipid phantoms in the 600-1850 nm wavelength range has been investigated. A set of 57 liquid optical phantoms, covering a wide range of intralipid concentrations (1-100% v/v), was prepared and the bulk optical properties were accurately determined. The bulk scattering coefficient as a function of the particle density could be well described with Twersky's packing factor (R(2) > 0.990). A general model was elaborated taking into account the wavelength dependency and the effect of the concentration of scattering particles (R(2) = 0.999). Additionally, an empirical approach was followed to characterize the effect of dense packing of scattering particles on the anisotropy factor (R(2) = 0.992) and the reduced scattering coefficient (R(2) = 0.999) of the phantoms. The derived equations can be consulted in future research for the calculation of the bulk scattering properties of intralipid dilutions in the 600-1850 nm range, or for the validation of theories that describe the effects of dependent scattering on the scattering properties of intralipid-like systems.

Supercontinuum laser based optical characterization of Intralipid® phantoms in the 500-2250 nm range

A supercontinuum laser based double integrating sphere setup in combination with an unscattered transmittance measurement setup was developed and carefully validated for optical characterization of turbid samples in the 500-2250 nm wavelength range. A set of 57 liquid optical phantoms, covering a wide range of absorption and scattering properties, were prepared and measured at two sample thicknesses. The estimated bulk optical properties matched well for both thicknesses, and with theory and literature, without significant crosstalk between absorption and scattering. Equations were derived for the bulk scattering properties μ(s), μ(s)' and g of Intralipid® 20% which can be used to calculate the bulk scattering properties of intralipid-dilutions in the 500-2250 nm range.

Recent progress in tissue optical clearing

Tissue optical clearing technique provides a prospective solution for the application of advanced optical methods in life sciences. This paper gives a review of recent developments in tissue optical clearing techniques. The physical, molecular and physiological mechanisms of tissue optical clearing are overviewed and discussed. Various methods for enhancing penetration of optical-clearing agents into tissue, such as physical methods, chemical-penetration enhancers and combination of physical and chemical methods are introduced. Combining the tissue optical clearing technique with advanced microscopy image or labeling technique, applications for 3D microstructure of whole tissues such as brain and central nervous system with unprecedented resolution are demonstrated. Moreover, the difference in diffusion and/or clearing ability of selected agents in healthy versus pathological tissues can provide a highly sensitive indicator of the tissue health/pathology condition. Finally, recent advances in optical clearing of soft or hard tissue for in vivo imaging and phototherapy are introduced. [Formula: see text].

Enhanced optical clearing of skin in vivo and optical coherence tomography in-depth imaging

The strong optical scattering of skin tissue makes it very difficult for optical coherence tomography (OCT) to achieve deep imaging in skin. Significant optical clearing of in vivo rat skin sites was achieved within 15 min by topical application of an optical clearing agent PEG-400, a chemical enhancer (thiazone or propanediol), and physical massage. Only when all three components were applied together could a 15 min treatment achieve a three fold increase in the OCT reflectance from a 300 μm depth and 31% enhancement in image depth Z(threshold).

Quantitative analysis of dehydration in porcine skin for assessing mechanism of optical clearing

Dehydration induced by optical clearing agents (OCAs) can improve tissue optical transmittance; however, current studies merely gave some qualitative descriptions. We develop a model to quantitatively evaluate water content with partial least-squares method based on the measurements of near-infrared reflectance spectroscopy and weight of porcine skin. Furthermore, a commercial spectrometer with an integrating sphere is used to measure the transmittance and reflectance of skin after treatment with different OCAs, and then the water content and optical properties of sample are calculated, respectively. The results show that both the reduced scattering coefficient and dehydration of skin decrease with prolongation of action of OCAs, but the relative change in former is larger than that in latter after a 60-min treatment. The absorption coefficient at 1450 nm decreases completely coincident with dehydration of skin. Further analysis illustrates that the correlation coefficient between the relative changes in the reduced scattering coefficient and dehydration is ∼1 during the 60-min treatment of agents, but there is an extremely significant difference between the two parameters for some OCAs with more hydroxyl groups, especially, glycerol or D-sorbitol, which means that the dehydration is a main mechanism of skin optical clearing, but not the only mechanism.

Different optical properties between human hepatocellular carcinoma tissues and non-tumorous hepatic tissues in vitro

There has been an ongoing search for clinically acceptable methods for the accurate, efficient and simple diagnosis and prognosis of hepatocellular carcinoma (HCC). Optical spectroscopy is a technique with potential clinical applications to diagnose cancer diseases. The purpose of this study was to obtain the optical properties of HCC tissues and non-tumorous hepatic tissues and identify the difference between them. A total of 55 tissue samples (HCC tissue, n=38; non-tumorous hepatic tissue, n=17) were surgically resected from patients with HCC. The optical parameters were measured in 10-nm steps using single-integrating-sphere system in the wavelength range of 400 to 1800 nm. It was found that the optical properties and their differences varied with the wavelength for the HCC tissue and the non-tumorous hepatic tissue in the entire wavelength range of research. The absorption coefficient of the HCC tissue (1.48±0.99, 1.46±0.88, 0.86±0.61, 2.15±0.53, 0.54±0.10, 0.79±0.15 mm(-1)) was significantly lower than that of the non-tumorous hepatic tissue (2.79±1.73, 3.13±1.47, 3.06±2.79, 2.57±0.55, 0.62±0.10, 0.93±0.16 mm(-1)) at wavelengths of 400, 410, 450, 1450, 1660 and 1800 nm, respectively (P<0.05). The reduced scattering coefficient of HCC tissue (5.28±1.70, 4.91±1.54, 1.26±0.35 mm(-1)) and non-tumorous hepatic tissue (8.14±3.70, 9.27±3.08, 2.55±0.57 mm(-1)) was significantly different at 460, 500 and 1800 nm respectively (P<0.05). These results show different pathologic liver tissues have different optical properties. It provides a better understanding of the relationship between optical parameters and physiological characteristics in human liver tissues. And it would be very useful for developing a non-invasive, real-time, simple and efficient way for medical management of HCC in the future.

ASSESSMENT OF TISSUE OPTICAL CLEARING AS A FUNCTION OF GLUCOSE CONCENTRATION USING OPTICAL COHERENCE TOMOGRAPHY

One of the major challenges in imaging biological tissues using optical techniques, such as optical coherence tomography (OCT), is the lack of light penetration due to highly turbid structures within the tissue. Optical clearing techniques enable the biological samples to be more optically homogeneous, allowing for deeper penetration of light into the tissue. This study investigates the effect of optical clearing utilizing various concentrations of glucose solution (10%, 30%, and 50%) on porcine skin. A gold-plated mirror was imaged beneath the tissue and percentage clearing was determined by monitoring the change in reflected light intensity from the mirror over time. The ratio of percentage clearing per tissue thickness for 10%, 30% and 50% glucose was determined to be 4.7 ± 1.6% mm(-1) (n = 6), 10.6 ± 2.0% mm(-1) (n = 7) and 21.8 ± 2.2% mm(-1) (n = 5), respectively. It was concluded that while higher glucose concentration has the highest optical clearing effect, a suitable concentration should be chosen for the purpose of clearing, considering the osmotic stress on the tissue sample.