This PDF file contains the front matter associated with SPIE Proceedings Volume 11211, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Spatial frequency domain imaging (SFDI), a noncontact imaging technique using structured illumination with multiple wavelengths, has proved feasible for characterizing burns of different severities induced in porcine dorsum. However, translation to human clinical subjects may be subject to variation in tissue optical properties due to different skin types or body parts. To interrogate this potential difference in optical properties, SFDI was used to measure the reduced scattering coefficient (μ_s’ ) in patients of varying Fitzpatrick skin type groups at 10 anatomical locations on the body. These scattering values were compared against previously measured average μ_s’ values for burns in a porcine model. At 851nm, superficial partialthickness burns had a 12.6% higher μ_s’ than unburned porcine dorsum. Deep partial-thickness and had 12.9% higher average μ_s’ than unburned porcine dorsum, while full-thickness burns had 2.5% higher average μ_s’ than unburned porcine dorsum. The variation seen in scattering values at 851nm at one anatomical location (dorsal forearm) for the different skin type groups showed a 6.3% lower average μ_s’ in group 3 (skin types VVI) compared to group 2 (skin types III-IV). Average scattering values were 3.8% lower in group 1 (skin types I-II) compared to group 2 (skin types III-IV). The variation of μ_s’ at 851nm across multiple anatomical locations for the same skin type group (Group 1) was a 23% difference from the anatomical location with the highest average μ_s’ at 851nm (forehead) to the lowest (shin). These findings indicate that further consideration of skin type and location will be integral to the translation of classification techniques based μ_s’ measurements of porcine dorsum to human patients.

Micro-projection array patches (MAPs) are an alternative approach to deliver vaccine without using needles and syringe. MAPs achieve improved vaccination efficiency by introducing a microtrauma in the skin, but a comprehensive understanding of all mechanisms behind this response remains elusive. Spatial frequency domain spectroscopy (SFDS) was used to quantify skin reactivity. This optical technique enables characterization of the skin response by identifying (1) functional tissue parameters, (2) changes in tissue structure and (3) measures of tissue damage. In a preliminary investigation, measurements were performed on 12 subjects in whom the MAP was applied on the lower forearm.

Obesity leads to a higher risk of diabetes and cardiovascular diseases. Wearable devices can be used to manage and promote the healthy lifestyle among the obese by measuring heart rate, heart rate variability, perfusion, and pressure pulse-wave velocities. While operational challenges are common in wearable devices using electrical or thermal sensors, those with optical sensors are more robust. Current optical sensors rely on fluctuations in light intensity due to spatio-temporal variations in tissue absorption. The thick layer of adipose tissue in high body mass index (BMI) individuals strongly scatters light, reducing the optical contrast and signal to noise ratio. Moreover, higher BMI alters chemical concentrations— like water, oxygenation, and blood volume in the dermal layer— and thus the optical properties (OP). Although OP of the skin exists in literature, no study has strictly recorded the effect and magnitude of a higher BMI on them. In this study, we combine the spatial frequency domain spectroscopy (SFDS) with a multi-sensor blood flow imaging device (PulseCam) to characterize the OPs and monitor the vascularization in the obese. The effects of skin morphology and physiology on the performance of optical sensor are preliminarily investigated.

Radiotherapy is a common and effective treatment for certain breast cancers. One potential drawback from this therapy is the development of varying degrees of erythema that typically occur after the treatment has been completed. Currently there are no tools to quantify radiation-induced skin changes during and after radiation and the standardized scoring systems remain subjective. Developing these tools would not only allow clinicians to objectively assess patients, but could potentially inform them as to which patients are likely to develop more severe side effects. Spatial Frequency Domain Imaging (SFDI) is a non-invasive, non-contact imaging technique capable of quantitatively mapping tissue absorption and scattering properties that can be converted into tissue oxygen saturation, total hemoglobin concentration and reduced scattering coefficients. Here we present a study of 13 breast cancer patients that have been prescribed radiation therapy and imaged using SFDI before, during, and after radiation treatment over the course of several weeks. A preliminary analysis of the data shows increases in total hemoglobin concentration as high as 75% in the treated breast tissue compared to highs of 10% in control regions at the end of the radiation treatments. Additionally, changes in the reduced scattering coefficient as high as 25% in the treated breast tissue can be seen a week before the treatment is complete and hyperpigmentation is visible. The aim of this study is to characterize radiation induced changes in skin using SFDI in order to provide clinicians with a technology that can inform radiation protocols (such as dose, frequency and duration) thereby minimizing unnecessary skin toxicity while maximizing treatment efficacy.

Actinic keratosis (AK) is a common cutaneous neoplasm resulting from severe solar damage. Noninvasive diagnosis and grading of AK are important not just because of AK’s precancerous nature, but also due to the frequent presence of multiple AKs. Here we study the clinical applicability of in vivo harmonic generation microscopy (HGM) for the grading, diagnosis, and treatment assessment of AKs. As a result, 100% agreement on diagnosis and grading outcomes between HGM and traditional histopathology were obtained. Our study indicates the superior capability of in vivo HGM for diagnosis, grading, and treatment assessment of AKs.

Early diagnosis of melanoma is an ongoing challenge in dermatology and oncology. There is a special subgroup of melanocytic lesions that can be clinically and dermoscopically indistinguishable from early melanoma. The aim of the study was to improve the in vivo diagnostic possibilities for the differentiation of dermoscopic equivocal melanocytic lesions based on combination of multiphoton tomography (MPT) and optical coherence angiography (OCA). A multiphoton optical score (MPOS) for quantitative assessment of the melanoma features revealed by MPM was developed. OCA images were processed to calculate the vessel densities and the total lengths thin and thick vessels. Histopathological analysis separated the equivocal lesions into benign, melanoma in situ, and invasive melanoma. The MPOS value of benign lesions was significant lower than for the malignant ones. Quantitative analysis of OCA images revealed that the invasive melanoma type has the highest vessel density. The combined use of multiphoton tomography with MPOS calculation and quantification of optical coherence angiography data demonstrated a potential to discriminate all dermoscopic equivocal melanocytic lesions in vivo.

Recent development of visible light Optical Coherence Microscopy (i.e. Optical Coherence Tomography employing high numerical aperture Objective) has pushed the axial/transverse resolution limit to < 2 μm within tissues. Here, a fiber-based visible light Fourier domain (FD) Optical Coherence Microscopy system is presented, employing a 10x water immersion objective to achieve higher transverse resolution and reduced specular reflection when imaging human skin in vivo, using ~ 1-2 mW of incident power. Though with limited penetration depth, we demonstrated its application for in vivo imaging of human skin, and further measured the thicknesses of epidermis and dermo-epidermal junction. Furthermore, the total attenuation coefficient of the skin tissues was also estimated across epidermis and dermis.

Skin cancer is the most common form of cancer in North America, and melanoma is the most deadly form of skin cancer. Roughness assessment of epidermis has been shown to be valuable in detecting potential skin neoplasia. However, the existing roughness assessment techniques cannot also provide volumetric information. For greater insight, we propose polarization sensitive optical coherence tomography (PS-OCT) for skin assessment. The intensity channel of OCT visualizes the layered structure and surface roughness profile of skin in 3D. Furthermore, PS-OCT can simultaneously conduct polarization related measurements such as the degree of polarization uniformity (DOPU) in a separate imaging channel. Skin phantoms of different surface roughness ranging from 1 to 68 μm have been studied. It was observed that for rougher surfaces, the roughness can be quantified from the surface profile visible in the intensity channel. In smoother surfaces for which the profile is not sensitive, the DOPU decreases with roughness in a quantifiable correlation. The contrast in the DOPU channel is sensitive to polarization and phase fluctuations. Smoother surfaces tend to maintain the polarization state, whereas the height differences in a rougher surface contribute to larger phase shifts between light waves within the coherence volume, leading to greater depolarization. PS-OCT was also applied to in vivo imaging of human skin. The skin at the palm edge shows lower DOPU compared to the skin on the back of the hand, an indication of greater polarization state modification caused by skin roughness. PS-OCT can provide a comprehensive evaluation of skin, which has great potential for detecting melanoma.

Melanocytic lesions may occur in various areas of the skin and may eventually develop into malignant tissue types as a result of abnormal tissue growth. Although the gold standard for the diagnosis of melanoma is still a histopathological examination, dermatologists often use dermoscopic examination in their routine practice to reduce unnecessary excisions or to prevent misdiagnosis of clinically suspected melanocytic lesions. However, dermoscopic examinations may require special training and experience. Furthermore, even among experts, different evaluation results may occur. For these reasons, image processing and artificial intelligence application studies are performed on dermoscopic images based on information technologies developed in recent years. This study investigated the automatic classification of superficial spreading melanoma and nevocellular nevus using support vector machines. A publicly available and histopathologically verified MED-NODE data set (70 superficial spreading melanomas and 100 nevocellular naevi) was used. For the classification task, first, the energy distributions (power spectral densities) of each image in the spectral domain were obtained. Second, gray-level co-occurrence matrices were created, and the textural features of the matrices were extracted. Finally, the learning model was developed with these features as input for classification. Support vector machines were trained using validation methods, including holdout validation and stratified cross-validation. The hyperparameters were optimized using the regularization factor of 10, the radial basis kernel function, and the gamma factor of 0.0098. Using 10-fold cross-validation, we achieved a mean accuracy of 98.9% (+/- 0.01 standard deviation), 99.4% sensitivity, and 97.5% specificity.

Generative adversarial networks (GANs) are among the most interesting and powerful tools in deep learning. GANs are capable of efficiently generating realistic new images given a relatively small set of training examples, enabling many exciting possibilities in biophotonics. This tutorial will introduce the basic concepts and tools useful for creating GAN models. Additionally, several emerging applications of GANs in biophotonics will be covered, including: noise reduction, resolution enhancement, histological analysis, lesion detection, and lesion classification.

With over 4.3 million new cases in the U.S. every year, basal cell carcinoma (BCC), is the most common form of skin cancer. Pathologists must examine pathology images to diagnose BCC, potentially resulting in delay, error, and inconsistency. To address the need for standardized, expedited diagnosis, we created an automated diagnostic machine to identify BCC given pathology images. In MATLAB, we adapted a deep neural network image segmentation model, UNet, to train on BCC images and their corresponding masks, which can learn to highlight these nodules in pathology images by outputting a computer-generated mask. We trained the U-Net on one image from the dataset and compared the computer-generated mask output from testing on three types of images: an image from a different region of the same image taken with the same microscope, an image from a different tissue sample with a different microscope, and an image taken with a confocal microscope. We observed good, medium and poor results, respectively, illustrating that performance depends on the similarity between test and training data. In subsequent tests using data augmentation, we achieved sensitivity of 0.82±0.07 and specificity of 0.87±0.16 on N = 6 sample sections from 3 different BCCs imaged with the same microscope system. These data show that the U-Net performed well with a relatively few number of training images. Examining the errors raised interesting questions regarding what the errors mean and how they possibly arose. By creating a surgeon interface for rapid pathological assessment and machine learning diagnostics for pathological features, the BCC diagnosis process will be expedited and standardized.

Multiphoton tomography (MPT) has become a high-resolution label-free clinical imaging tool to obtain optical skin biopsies for rapid in vivo histology. Here, we report on the novel multimodal multiphoton tomograph MPT compact based on a chiller-free ultracompact 80 MHz femtosecond fiber laser operating at 780 nm. The 360°-measurement head contains the laser head and multiple photon detectors for (i) autofluorescence (AF) imaging, (ii) fluorescence lifetime imaging (FLIM) for optical metabolic imaging (OMI) and melanin detection, (iii) second harmonic imaging (SHG) of collagen, (iv) confocal reflection microscopy (CRM), and (v) white-light imaging (dermoscopy). Preliminary results of an ongoing multicenter clinical study in patients with suspicious pigmented lesions in two hospitals are presented.

Multiphoton microscopy (MPM) can provide sub-micron resolution images of living tissues in their native environment with contrast from multiple modalities, including second harmonic generation (SHG) and two-photon excited fluorescence (TPEF). Recent advances of MPM in clinical skin imaging demonstrated the unique potential of this technology as a label-free research and clinical tool for a broad area of applications such as melanoma and non-melanoma skin cancer detection, monitoring pigmentary skin disorders, characterizing keratinocyte metabolism, etc. In this contribution we demonstrate the ability of this microscope to provide sub-micrometer resolution ex-vivo images of large areas of skin tissue (up to 5x5 mm2) in <1 minute. We demonstrate the importance of high-speed, high-resolution mesoscopic imaging on cancerous skin tissues that present heterogeneous morphology to show the ability of the instrument to capture both benign and malignant areas of the lesion.

Through noninvasive monitoring of leukocyte motion in skin capillaries of patients after hematopoietic cell transplantation, we found increased leukocyte rolling and adhesion prior to clinical signs of disease. In this longitudinal pilot study, we explored the feasibility to detect changes in leukocyte-endothelial interactions that precede acute graft-versus-host disease in patients after hematopoietic cell transplantation. We present the pattern of change in leukocyte rolling and adhesion in three patients over the course of the first 100 days post-transplant. Our preliminary data show increased leukocyte-endothelial interactions prior to clinical signs of any organ acute graft-versus-host disease.

“Nik Kollias, the spectroscopy of melanin, and current advances in skin optics” was recorded at Photonics West BiOS 2020 held in San Francisco, California, United States.

A port-wine stain is a congenital vascular malformation, which may worsen if left untreated. Selective photothermolysis with Pulse-dye lasers is a well-established treatment for PWS. However, outcomes are often unpredictable due to tissue heterogeneity. This study characterizes the three-dimensional architecture of ex vivo human skin from control and PWS regions of five patients before and after laser treatment using optical coherence tomography (OCT), two-photon excitation fluorescence microscopy (TPEM), and second harmonic generation (SHG). Results suggest that combining the high penetration depth of OCT with the high resolution of multiphoton imaging could provide a means for real-time guidance of selective phototherapy.

We report a novel approach to selectively close single blood vessels within tissue using multiphoton absorption-based photothermolysis. The treatment process is monitored by in vivo reflectance confocal microscopy in real-time. Closure of single targeted vessels of varying sizes ranging from capillaries to venules was demonstrated. We also demonstrated that deeply situated vessels could be closed precisely while preserving adjacent overlying superficial vessels. Partial vessel occlusion could also be achieved, and it is accompanied by intravascular blood cell speed increasing. This approach provides a novel precision medicine method for non-invasive precise microsurgery treatment of vascular diseases on per vessel/per lesion basis.

Vitiligo is an autoimmune depigmentation disorder. Narrowband ultraviolet B (NB-UVB) phototherapy is currently the standard of care for generalized vitiligo. The combination of visible light (VL) with UVA1 (VL+UVA1) has recently been shown to induce skin pigmentation. This pilot study aims to compare the efficacy of VL+UVA1 versus NB-UVB phototherapy in subjects with vitiligo. Preliminary findings suggest a more robust erythematous response post-irradiation at VL+UVA1 site when compared to NB-UVB sites. Study results will provide information regarding optimal wavebands and associated parameters, including irradiance and dosing, that can result in skin repigmentation in vitiligo patients.

Optimization of laser-based therapeutic devices in dermatology requires a knowledge of the distribution of laser fluence at different depths in skin. This distribution is particularly difficult to estimate or measure when the laser is focused into skin, due to high scattering and strong aberrations. An inaccurate estimation of the fluence at the target depth may result in adverse events or a lack of the desired therapeutic outcome. Estimates of fluence distribution in tissue from Monte Carlo simulations are only as good as the assumed geometrical model of skin and the choice of scattering and absorption coefficients, which vary widely in literature. Here we present a novel technique for directly measuring the spatial distribution of fluence in skin under a focused laser beam. A commercial grade CMOS camera was modified to allow tissue to be placed in direct contact with its sensor. Fluence distribution was measured from captured images followed by simple post processing. The thickness of skin samples was measured using OCT before mounting on the sensor. With a 0.5NA lens and a pulsed 1064nm laser focused through murine skin samples of different thickness, the fluence distribution was mapped as a function of thickness. The spread of energy was substantially larger than the diffraction limited spot that would be expected in the absence of scattering and aberrations. The measurements agree well with transmitted energy measured through tissue using a pinhole mounted on an integrating sphere. The experimental results are compared with Monte Carlo simulations and limitations of the simulation are also discussed.

Vitiligo is characterized by white patches on skin due to the loss of melanocytes. Treatments are not uniformly successful and re-pigmentation is rarely complete. Optical laser scanning microscopy techniques have great potential to advance our understanding of the repigmentation process of vitiligo. In this pilot study, we employ in-vivo multiphoton microscopy (MPM) to assess potential changes in the metabolic state of epidermal keratinocytes involved in vitiligo before and throughout treatment, and in-vivo reflectance confocal microscopy (RCM) to assess the initiation of the re-pigmentation process and monitor wound healing after micro-grafting treatment.

We examined the relationship between depth-resolved local optical properties of eye-corner skin measured by multifunctional Jones matrix optical coherence tomography (JM-OCT) and corresponding wrinkle morphology of aged women (n=21; age range, 71.7±1.7). Wrinkle morphology parameters were analyzed by measuring surface topography of three-dimensional silicone replicas. The same regions were measured three-dimensionally by JM-OCT and the means of several optical properties were computed at each depth. Optical properties include birefringence (BR), attenuation coefficient (AC), and degree-of-polarization uniformity (DOPU). BR and AC were correlated with mean wrinkle depth (WD), although DOPU was not. Significant correlations were found between WD and BR at 88.2 to 138.6 μm depth region from the skin surface (highest correlation at 113.4 μm), and between WD and AC at 12.6 to 18.9 μm and 189 to 459.9 μm depth regions from the skin surface (highest correlations at 18.9 μm and 415.8 μm). This suggests that the collagen structure of the papillary dermis and the microstructure and/or tissue density of the upper epidermis and reticular dermis may be associated with wrinkle morphology. Multiple regression analysis was used to examine the highest significant correlations of BR (113.4 μm) and AC (18.9 μm, 415.8 μm). A significant regression coefficient (R²=0.547, p = 0.001) was obtained, indicating that only BR and AC could sufficiently explain WD. Beta coefficients of BR (113.4 μm), AC (18.9 μm), and AC (415.8 μm) were −0.384, −0.369, and −0.354, respectively. This suggests that the upper epidermis, papillary dermis, and reticular dermis may contribute similarly to wrinkle formation.

The use of non-invasive imaging techniques in dermatology has been reported to improve the diagnostic accuracy and the practice of biopsies, and at the same time to reduce the need for tissue excision. However, the current clinically-available imaging techniques do not yet entirely meet the need for early and accurate, non-invasive detection of all skin cancers. A handheld line-field confocal optical coherence tomography (LC-OCT) device has been designed for high-resolution non-invasive imaging of human skin, in vivo. LC-OCT delivers tomographic images in real-time (10 frames/s) with a quasi isotropic spatial resolution of ~ 1 μm, revealing a comprehensive morphological mapping of skin tissues at a cellular level, down to a depth of ~500 μm. The device has been applied to the in vivo imaging of various skin lesions. Surgical excisions of the lesions have then been performed followed by tissue processing to realize H&E-stained histopathological images. The spatial resolution, orientation, and imaging contrast mechanism of the LC-OCT images have allowed for a good level of similarity with the conventional histopathological images. LC-OCT was able to show most of the histopathological elements that allow for medical diagnosis. Using handheld LC-OCT as an adjunct tool in dermatology could help improve clinical diagnostic accuracy, allowing for the early detection of malignant skin tumors and a reduction in the number of surgical excisions of benign lesions.

Optical coherence tomography angiography (OCTA) provides in-vivo images of microvasculature. In skin it often represents a dynamic perfusion state without depicting the actual extent of the vascular network. Here, we present the capillary refill method for obtaining a more accurate anatomic representation of surface capillary networks in human skin using OCTA. OCTA images were captured at baseline displaying ambient capillary perfusion and after compression and release of the skin representing the network of existing capillaries at full capacity. This method provides mapping of cutaneous capillary networks independent of ambient perfusion comparable to histological analysis of biopsies on identical skin sites.

Skin and soft tissue infections (SSTIs) are one of the most common infections in India affecting 10-12% of Indian population. They are caused by a variety of bacteria and fungus, which makes it harder to diagnose and propose an effective treatment immediately especially in low resource settings due to the lack of access to qualified physicians. Management of SSTIs requires early expert infection assessment and remains a major challenge for the clinicians. A hand-held device is developed leveraging the inherent autofluorescence properties of the bacterial and fungal species that can non-invasively and rapidly identify the pathogens on SSTI using multispectral imaging followed by image processing and machine learning algorithms. The device is able to classify the gram type with < 85% accuracy.

To follow the development of pigment disorders like vitiligo over time, a newly developed full spectral modified ‘UV camera’ was introduced to enhance the image quality of vitiligo lesions in comparison to conventional images and surface area drawings. The quality of 31 images of lesions was assessed as good for 100% for the UV camera and 26% for the conventional camera by experts. The intraclass correlation coefficients (ICCs) of the lesion size between the imaging techniques were > 0.98. The UV camera provides high contrast images and enables the assessment of vitiligo lesions and accurate quantification of the surface area.

We have recently introduced a novel methodology for noninvasive assessment of structure and composition of human skin in vivo1. The approach combines pulsed photothermal radiometry, involving time-resolved measurements of midinfrared emission after irradiation with a millisecond light pulse, and diffuse reflectance spectroscopy in visible part of the spectrum (400–600 nm). The experimental data are fitted simultaneously with respective predictions from a fourlayer Monte Carlo model of light transport in human skin. The described approach allows assessment of the contents of specific chromophores (melanin, oxy-, and deoxy-hemoglobin), as well as scattering properties and thicknesses of the epidermis and dermis.

In present study we evaluate the potential of this approach for quantitative evaluation of tattoos. For this purpose, we apply a three-layer optical model of skin consisting of epidermis, upper dermis, and bottom dermis which includes the tattoo ink. The study involves healthy volunteer with black tattoo undergoing tattoo removal treatment with Q-switched Nd:YAG laser. The measurements are performed in four tattoo sites and one nearby healthy site before and after laser removal treatment. The results indicate the depth of tattoo, amount of tattoo ink and scattering properties in the dermis. This information can be used to improve our understanding of laser tattoo removal procedure.

This talk highlights a novel instrument for real-time video-rate imaging of microcirculation blood flow. The instrument utilizes multi-exposure laser speckle contrast imaging (MELSCI) with a high-speed camera, custom integrated electronics, and machine learning for massive computational bandwidth. This instrument enables, for the first time, continuous in vivo imaging of blood flow at frame rates sufficiently high to track dynamic changes, with perfusion estimates strongly correlated with that of laser Doppler flowmetry (LDF). This is an important step enabling a better understanding of the role of the microcirculation in several cardiovascular diseases. A pilot study on healthy subjects is presented.

Assessment of bruise age in forensic investigations is based on skin discoloration due to dynamic processes involving extravasated hemoglobin and products of its biochemical decomposition. However, the current protocol relies exclusively on visual inspection and subjective assessment by a medical expert. We are aiming at development of an objective and more accurate approach to aging of bruises by utilizing two optical techniques: Diffuse reflectance spectroscopy (DRS) and pulsed photothermal radiometry (PPTR).

This report involves two human volunteers with bruises acquired incidentally at a known time point. DRS spectra in visible spectral range are obtained from laterally uniform lesion sites using an integrating sphere. PPTR measurements involve irradiation with a millisecond laser pulse at 532 nm and recording the resulting transient change of mid-infrared emission with a fast infrared camera. Data from both measurements are analyzed simultaneously by fitting with predictions from a dedicated numerical simulation of light and heat transport in a multi-layer model of human skin. The results show a prominent increase of the dermal hemoglobin content and reduction of its oxygenation level relative to a nearby intact site (resulting from blood extravasation), followed by a rise of the bilirubin content. The parameters of a simple dynamical model of a self-healing bruise are then assessed by fitting together a set of experimental data acquired at different times post injury. The results indicate a rise and subsequent decrease of the hemoglobin decomposition rate, as the inflammatory response first kicks in and then gradually subsides.

In this study, the severity of canine skin erythema was assessed objectively for the first time. Atopic dermatitis (AD) is a common canine inflammatory and pruritic skin disease associated with an allergic reaction to exogenous allergens. The monitoring of skin erythema over time with lesion severity scales like the CADESI-4 is an essential diagnostic and research tool, especially for clinical trials. Currently, the erythema assessment is subjective due to visual estimation. In our study, we calculated the erythema index (EI) in 14 atopic dogs based on the analysis of multispectral skin images taken with the Skimager device. The relationship between the EI and a visual erythema estimation was modeled by linear regression with the first-order polynomial. The coefficient of determination (r squared) reached 0.81. Based on such high correlation, we conclude that optical measurements could replace the visual estimation of erythema in atopic dogs and, thus, improve the validity of skin lesion severity scales in dogs.

Line-field confocal optical coherence tomography (LC-OCT) is an imaging method based on dynamically-focused line-field time domain OCT to generate cellular resolution images of biological tissues, either in vertical sections (cross-sectional) or in horizontal sections (en face), with field of views of 1.2 × 0.5 mm² (horizontal) and 1.2 × 0.4 mm² (vertical). A handheld LC-OCT probe has recently been developed to facilitate the use of this imaging technique in dermatology for non invasive detection of skin cancers. We present here a video mosaicking method to reconstruct LC-OCT images with extended fields of view from a sequence of images obtained by a free displacement by the user of the LC-OCT probe on the skin surface. The lateral field of view is extended in both vertical and horizontal section images to ~ 5 mm, while maintaining an isotropic spatial resolution of ~ 1 μm. LC-OCT imaging with video-mosaicking is demonstrated for following the edges of large skin structure, as a proof-of-principle of in vivo tumor margin delineation, and for extending the lateral field of vertical section images, in order to approach the field of view of histology in this direction.

The orientation and concentration of structures like collagen within biological tissues can provide valuable information, for example, in skin disease diagnostics. Polarimetry lends itself for non-destructive investigation in various fields of research and development ranging from medical diagnostics to production monitoring, among others. We report on a system for polarimetric measurement of versatile targets in reflection and transmission mode. It efficiently determines the Mueller matrix (MM) of a sample under study and is also suited for in vivo applications. Generally, the Mueller matrix M_m allows to calculate the Stokes vector So of the light interacting with a sample, containing all information on its polarization properties, through S_o = M_m S_i where S_i is the Stokes vector of the illuminating light. The Mueller matrix can be derived from images taken with different polarization states of illuminating and observed light. In our setup we use liquid crystal retarders to precisely control the polarization states of the light. This enables fast measurement of the orientation of structures with high spatial resolution. In a first example, we demonstrate the capability of our system by characterizing electrospun fiber tissue implants and measuring the degree of alignment and orientation of the fibers in reflection mode. The results lead us to a deeper understanding of the signals which we expect from structures like collagen in skin. We were able to derive a correlation between the properties of the tissue structures, the parameters for production and the MM information, for the first time. This was possible by suitable decomposition of the MM into submatrices of known physical interpretation. In this work we present our latest results and discuss the next steps towards in vivo application in dermatology or tissue implant.