This PDF file contains the front matter associated with SPIE Proceedings Volume 11585, including the Title Page, Copyright Information, and Table of Contents.

A brief review on the activities of Biophotonics Laboratory at UL Institute of Atomic Physics and Spectroscopy, following the previous Biophotonics Riga - 2017 conference, is presented. Twelve recent research projects are considered, including two EC Horizon-2020 projects, six European Regional Development Fund projects and four projects funded by the Latvian Council of Science. The projects are generally aimed at development of new optical methods and technologies for noninvasive in-vivo skin assessment to facilitate early diagnostics of skin malformations (including cancers), sepsis and cutaneous blood microcirculation features. Most of the projects explore novel approaches of camera-based biomedical imaging for clinical diagnostics and recovery monitoring.

The concept of ‘tissue optical windows’ and method of optical clearing (OC) based on controllable and reversible modification of tissue optical properties by their soaking with a biocompatible optical clearing agent (OCA) are prsented. Fundamentals and major mechanisms of OC allowing one to enhance optical imaging facilities and laser treatment efficiency of living tissues are described. Perspectives of immersion optical clearing/contrasting technique aiming to enhance optical imaging of living tissues by using different imaging modalities working in the ultra-broad wavelength range from deep UV to terahertz waves are discussed. It demonstrated that immersion OC method can be applied to evaluate the characteristic diffusion properties of water and OCA in various tissues and even discriminate between the mobile water content in normal and pathological tissues.

We investigated pigmented skin tumour lesions in vivo and ex vivo, including benign and dysplastic nevi, as well as malignant lesions, such as pigmented basal cell carcinoma (BCC) and malignant melanoma (MM) lesions, to obtain a complex view about the feasibility of different excitation sources solely and/or in combination to induce fluorescence signal useful for diagnosis of various low-fluorescent cutaneous neoplasia. A specialized multispectral analysis of the data obtained was applied by using excitation in broad spectral range, covering ultraviolet, visible and near-infrared spectral range, that contribute considerably to: (1) fundamental determination of tumour tissues’ spectral properties, and (2) to increase the accuracy in determining the type of cutaneous pathology. The chromophores, related to the formation of ultraviolet and visible (UV-VIS) fluorescence in human normal skin and its pigmented lesions are mainly amino acids – tryptophan, tyrosine; structural proteins and their cross-links – collagen, elastin, keratin; co-enzymes - NADH, flavins; vitamins and lipids. In the near-infrared (NIR) spectral region, skin fluorescence emission properties are related to the presence of melanin pigment, lipids and endogenous porphyrins, if any, as the highest impact on the resultant emission spectrum is due to the melanin compound.

Measuring blood perfusion is important in medical care. However, currently available devices to measure blood perfusion are bulky, expensive and not easy-to-use. In this work a compact and portable low-cost prototype device for remote monitoring of palm skin microcirculation has been developed. Presented device consists of precisely controlled near-infrared illuminators (760nm peak wavelength) and video camera. The device with the custom designed software provides stable uniform illumination of curved skin surfaces, using feedback algorithm. Verification tests of this device showed improvements in the quality of skin blood perfusion maps in the case when the feedback system was used.

Skin cancer is the most common type of cancer in the USA and worldwide.¹ An early diagnosis is the key to a successful treatment. Among the skin cancers, the malignant melanoma (MM) accounts for 1% of the cases while it is responsible for the majority of deaths. Basal cell carcinoma (BCC) is the most common form of skin cancer with a very low mortality rate.² Unfortunately, skin cancer recurrence is a common problem for MM and BCC patients. We propose a post-operative scar screening with non-invasive autofluorescence (AF) imaging to detect an early growth of any residual tissue from the cancer removal procedure. The screening images can serve also as a visual evidence for the post-op patient’s observation in dynamics. The results of the study show promising results comparing various post-op scars with recurrent cancer cases.

Peripheral neuropathy refers to peripheral nervous system dysfunction which affects up to 2% of the world's population. This condition is caused by damage to the small nerve fibers, hence its assessment is still challenging due to the lack of simple, non-invasive and objective diagnostic techniques. The present study aimed to develop and evaluate a simple, objective and non-invasive technique for assessment of small cutaneous sensory nerve fiber function. Our approach is based on utilization of imaging photoplethysmography and local skin heating. The effectiveness of the method was evaluated on young, healthy volunteers (n = 14) after 10 minutes of 45-degree local skin heating, while recording a photoplethysmographic signal simultaneously from the intact (control) and anesthetized skin (topical application of Emla gel) regions. In the anesthetized skin region, the local heating evoked flare area was 44% lower than that of intact skin. A similar trend was observed for the perfusion curve- perfusion peak in the anesthetized skin was substantially reduced in comparison to intact. The results indicate for the potential of the imaging photoplethysmography in the assessment of the small nerve fiber function. It is believed that this technique could be utilized in the clinics in the future to examine neuropathy patients and diagnose neuropathy.

Gum disease caused by bacterial infection, systemic conditions or neurogenic inflammation remains a prevalent and important concern of public health in both, developing and developed countries, potentially causing tooth loss if left untreated. Therefore, a simple, cost-effective, and contactless diagnostic tool is needed in dentistry. The present study aims to develop and investigate the feasibility of a motion artefact-free, miniature imaging photoplethysmography system which is dedicated for assessment of gingivitis in the dental office. The device comprised of a sub-miniature monochromatic camera equipped with miniature lens, 4-LED ring illuminator, cross polarizers and bandpass optical filter (CW=540nm, FWHM=25nm). The present pilot study comprised six subjects. The transitory neurogenic gingival inflammation has been induced by topical application of capsaicin containing chilli extract. The photoplethysmography signal was acquired from the same site before and after inflammation, and perfusion maps were computed. During the procedure, the developed imaging system demonstrated motion artefact-free data recordings and high signal to noise ratio. As expected, topical application of chilli extract produced noticeable transitory neurogenic inflammation, detected in perfusion maps. The present findings confirm the potential of imaging photoplethysmography for gingival tissue inflammation assessment, and in the future could be utilized in the dental office.

The study aimed to test laser speckle contrast imaging for fast and non-invasive assessment of ultrasound induced bactericidal effect on C. albicans biofilm. Low frequency sonication applied at 1.1 MPa peak negative pressure for 1 min reduced the number of viable C. albicans cells. The bactericidal effect was related to the spectral contrast decrease resulting from the standard deviation decrease within the speckle pattern as compared to the unchanged mean intensity. C. albicans biofilm recovered completely within 41 h after sonication. The recovery of biofilm was represented by increase of speckle contrast parameter. We foresee that speckle-based technique would be helpful for the efficacy assay of microbial biofilm inactivation.

We explore the potential for noninvasive monitoring of laser tattoo removal treatment by adapting a recently introduced methodology for quantitative assessment of structure and composition of human skin in vivo.¹ The approach combines diffuse reflectance spectroscopy in visible part of the spectrum with pulsed photothermal radiometry, involving timeresolved measurements of mid-infrared emission after irradiation with a millisecond laser pulse. The experimental data are fitted simultaneously with the respective predictions of a dedicated numerical model of light and heat transport in tattooed skin. For this purpose we apply a three-layer optical model of skin, consisting of epidermis, upper dermis, and lower dermis which includes the tattoo ink. This proof of principle study involved one healthy volunteer undergoing tattoo removal treatment. One half of the tattoo was treated with 5 ns pulses from a commercial Nd:YAG laser (StarWalker® MaQX, Fotona) at radiant exposure of 3 J/cm², and the other half with much shorter, "picosecond" pulses at the same wavelength and 1.3 J/cm². Measurements were performed before and 8 weeks after the first treatment session, as well as 20 weeks after the second treatment. The results show a significant reduction of the ink content and an increase of the subsurface depth of the tattoo layer over the course of treatment with both lasers, in agreement with gradual fading of the tattoo.

High-frequency electrodeless light sources are known as bright radiators with the line spectrum, characterized by high intensities and narrow line shapes. The lamp balloons are mostly made of quartz and filled with a metal and buffer gas. These light sources must be optimized for each application in accordance with the specific requirements of radiation quality, lifetime, and stability. This work is devoted to the diagnostic of high-frequency electrodeless light sources for their use in high precision atomic absorption analyzers and other applications like disinfection. The spectral line intensities and profiles were studied in discharges with arsenic and thallium fillings. Special attention is devoted to the UV lines of 193.7 nm and 197.2 nm of As and 377.6 nm of Tl spectral lines. The intensities and profiles were measured by means of a Fourier transform spectrometer. The deconvolution procedure was implemented to obtain the real form of emitted profiles for further analysis. The integrated areas, values of self-absorption, and other parameters were obtained and compared for both fillings as a function of working regimes.

This work will describe the challenges involved in setting up automatic processing for a large differentiated data set. In this study, a multispectral (skin diffuse reflection images using 526nm (green), 663nm (red), and 964nm (infrared) illumination and autofluorescence (AF) image using 405 nm excitation) data set with 756 lesions (3024 images) was processed. Previously, using MATLAB software, finding markers, correctly segmenting images with dark edges and image alignment were the main causes of the problems in automatic data processing. To improve automatic processing and eliminate the use of licensed software, the latter was substituted with the open source Python environment. For more precise segmentation of skin markers and skin lesions, as well for image alignment, the processing of artificial neural networks was utilized. The resulting processing method solves most of the issues of the MATLAB script. However, for even more accurate results, it is necessary to provide more accurate ground-truth segmentation masks and generate more input data to increase the training image database by using data augmentation.

The number of research papers, where neural networks are applied in medical image analysis is growing. There is a proof that Convolutional Neural Networks (CNN) are able to differentiate skin cancer from nevi with greater accuracy than experienced specialists on average (sensitivity 82% and 73% accordingly).¹ Team's latest research² allows achieving even greater accuracy, by using specific narrow-band illumination. Nevertheless, the overall probability of early skin cancer detection depends on the availability of diagnostic tools. If screening tools will be available to a high number of general practices, the chance of disease detection will increase. The previous research³ shows that scalable cloud service is able to process a high number of users. After a certain number of users, the overall cost of the system, including cloud processing expenses and cost of high computational power portable device, might be higher if compared to an on-premises solution, where each device is capable of diagnosing without Internet access. It might be cheaper to equip devices with additional neural processing unit (NPU) and exclude cloud processing. Another option is to make screening available by using the newest smartphones that are equipped with NPU.⁴ The problem of using the NPU is that they are limited in storage space, accuracy, and features. Therefore, a full-size CNN model should be adapted and minimized to fit in a limited NPU. Research reviews existing CNN optimization methods and proposes the most accurate for skin cancer diagnostics. The paper evaluates CNN prediction losses when the model's elements’ precision is reduced from 32 bits to 8 and rounded to integer values.

Canine atopic dermatitis (CAD) is a common inflammatory and pruritic skin disease associated with allergy to exogenous allergens. The regular monitoring of skin lesions is essential to execute the anti-allergic therapy successfully. Erythema is one of the most important CAD-related lesions since it represents acute skin inflammation. Previously, we studied two optical systems (i.e., multispectral and dermatoscopic devices), which could objectively estimate erythema severity. However, we did not investigate, which image sampling method for selecting erythema-representing pixels and erythema index (EI) are correlated with the visual erythema assessment the most. In this paper, we tested three image sampling methods and four EIs for erythema severity estimation in 43 dogs. We discovered that all studied sampling methods and EIs were strongly correlated (r> 0.58) with the visual CADESI-4-based erythema severity assessment. However, the highest average Spearman’s correlations coefficient r of 0.77 was achieved when the average pixel value from the two small squared image sections without the hair and pigment was considered. On the other hand, EI, which was calculated from all three RGB values, achieved the highest r of 0.78. In this study, we identified a reliable image sampling method and erythema index (EI), which are well correlated with the visual erythema estimation.

Photoplethysmography (PPG) has proved to be valuable signal carrier information from many biomedical sources. Especially, sauna studies have shown that heart pulse inter beat intervals, heart rate variability (HRV), shape and morphology of PPG can provide much interesting information about arterial elasticity during and after a sauna exposure. These parameters are pulse amplitude, pulse width, and pulse to pulse beat intervals changes caused by the sauna exposure. In our preliminary study there is searched on heart pulse variability information and other hemodynamic parameters. However, there is not yet standard detailed calculation algorithms for these parameters. Merged Poincaré plots, or so called return maps, could give valuable information which is here at the first time noticed.

Our work is focused to develop sensitive optical diagnostic methods for the detection of Volatile Organic Compounds in the breath. For the breath measurements, we have built a cavity ring-down spectrometer, operated in the UV region. The system was tested and calibrated using a KinTek automated permeation tube system with nitrogen as a carrier gas, as well as self- prepared acetone mixtures in air with known concentrations. In this paper, we present results of the measurements of acetone concentration in the breath for the test group of randomly selected 40 people in the age group over 50. We observed the values of acetone concentration in the breath in the range from 0,1 – 80 ppm, with a median 7,1 ppm. The experiments showed that the limits of detection for acetone with the cavity ring-down system are several tens of ppb.

It has been established recently that acousto-optic devices based on Bragg cells can be used for the bioelectric signals spectral processing. This processing can be realized only if acousto-optic spectrum analyzers with time or time-andspace integration are used. The frequency range of the processing system is defined by the complex of the acousto-optic Bragg cell and multielement photodetector characteristics. Two possible principles of the photodetector characteristics have been considered – direct and reverse principles. It has been shown that two parameters of photodetector play especially important part for the signal processing by means of acousto-optic device: charge accumulation time which defines the lower boundary of analyzed frequency range, and number of pixels per one resolvable interval which defines the upper boundary. The performed analysis has shown that the requirements for the second parameter are strongly defined by the investigated signal dynamic range, any distortion of which can produce the loss of important diagnostic information. It also has been shown that the correct choice of photodetector characteristics provides the acousto-optic processing system applicability for bot electrocardiographic and electroencephalographic signals obtained in the ultra high resolution mode.

Endoscopes are applied widely for diagnostics of different diseases of internal organs. However, simultaneous transmission of spectral and spatial information by means of even the most perfect endoscopes meets significant obstacles. A new kind of endoscope has been proposed in this paper, in which the image of internal organ is transmitted not only by video camera but also some certain fragments of the image are transmitted by the image transmitter based on fiber optics. This composition provides elimination of the information losses which are connected with three-colored principle of television image transmission. Additional spectral information increases the reliability of diagnoses made on the base of data presented by endoscope. The structural circuit of the proposed endoscope has been considered and discussed. The most common area of practical application of this endoscope is internal organs oncology diagnostics. In order to perform such diagnostics, some preliminary investigations are required because the reflection spectra of human tissues defeated by the cancer cells, are not yet known. Such hybrid endoscope can be used in gastroscopy, bronchoscopy, colonoscopy, laparoscopy, and all other similar areas. The principle of multispectral processing which is used in fiber-optics-based sensors provides obtaining of maximum possible spectral information in addition to high spatial resolution provided by RGB camera.

The method of multispectral images processing foresees the simultaneous processing of several kinds of information, preferably spatial , spectral, and gradational kinds. The reliable recording of these kinds of information causes in many cases the time information losses which is often look undesirable. However if the selective element operation rate is enough high, as it takes place in the case of acousto-optic tunable filters application, so it is possible to minimize the losses of time information. The mutual dependencies of amounts of different information kinds have been considered during their transmission while the images multispectral processing procedures. The special attention have been paid to the definition of spatial and spectral information relationships optimums as well as the same for spatial and gradational information. The areas of medical diagnostics have been discussed for which the multispectral processing method application can increase the probability of the correct diagnostic solutions accepting significantly.

Multispectral processing of images provides decreasing of information losses regarding spectral composition of an image. This method application produces the reflection spectrum of the observed object in each its point. It is especially efficient if an imaging acousto-optic tunable filter is used as a diffraction element of the processing system. We have proposed to use the multispectral processing of skin lesions images in order to find the possible signs of malignancies of patient’s skin. Multispectral processing method provides the visualization of the reflection patterns of the skin lesions, and the patterns at wavelengths which are inherent to the reflection from the malignancies, will show haw the certain kind of malignancy is spatially distributed inside the skin lesion to be studied. The preliminary investigations must be performed in order to determine the specific light wavelengths which are characteristic reflection wavelengths for different kinds of malignancies. The selection of spatial areas where the malignancy is found and detecting the places not occupied by the malignancy is very useful for successful treatment. The functional circuit of the device providing the multispectral processing of skin lesions images, has been presented and discussed. Keywords: multispectral processing, malignancies, skin lesions, information productivity, acousto-optic tunable filter, fine wavelength tuning