This PDF file contains the front matter associated with SPIE Proceedings Volume 11640 including the Title Page, Copyright information, and Table of Contents.

Introduction to SPIE Photonics West BiOS conference 11640: Optical Interactions with Tissue and Cells XXXII

A new picosecond laser (Impulse+, Irisiome, France) with bursts of ultrashort pulses was recently proposed for tattoo removal to enhance efficiency and patient tolerance. This study aims to analyse the optical properties of tissues and cells of the skin subject to laser irradiation with or without black ink pigments. Results show that black tattoo ink alone is not cytotoxic for dermis cells but it can induce particular cells’ reactions up to death with laser irradiation. These results are promising and help understanding picosecond laser process for tattoo removal.

Pulsed lasers with ultrashort pulse durations have become ubiquitous in a variety of applications, including laser eye surgery. Therefore, the role of nonlinear optical effects, such as supercontinuum generation, needs to be considered when evaluating their potential hazard. We used a NIR femtosecond laser to generate a supercontinuum within an artificial eye. We recorded the visible spectra of the supercontinuum generated and calculated the energy contained within the visible band. Our results indicate that for certain exposure conditions, the supercontinuum’s energy within the visible range surpasses the maximum permissible energy allowed for visible wavelengths by the laser safety standards.

In picosecond laser treatments for pigmented skin lesions, selective optical absorption by melanin particles packaged in cutaneous melanosomes results in producing treatment effects. The treatment effects have been numerically analyzed by simulating light propagation and thermal diffusion at a tissue scale. During picosecond laser irradiation, cutaneous melanosomes are disrupted by explosive vaporization through optical absorption by melanin particles. A multiscale modeling of picosecond laser skin treatments is required for the quantitative evaluation of picosecond therapeutic laser devices. By the multiscale modeling, the treatment effects can be evaluated based on the interactions with picosecond laser pulses at each scale of molecule, organelle, cell, and tissue. For the multiscale modeling, the purpose of this study is to investigate a response of melanin particles to picosecond laser pulses at a molecular scale. Homogeneous melanin suspensions were prepared to irradiate 550-picosecond laser pulses at a wavelength of 755 nm. As a result of comparing morphological characteristics between unirradiated melanin particles and melanin particles irradiated by picosecond laser pulses with a scanning electron microscope and a particle size analyzer using dynamic light scattering, almost no significant change was found. The results suggested that melanin particles do not change the structures and are involved as a heat source to cause damage on lipid bilayer membranes within melanosomes in picosecond laser treatments for pigmented skin lesions.

Hyperspectral imaging has emerged as a promising diagnostic technique in the medical field. However, reflection from a sample often consists of a combination of surface reflection (also known as glare) and volume reflection. In this study, we propose a method to separate these two by illuminating the samples from three different angles and using a least squares optimization. This widely applicable method showed an adequate distinction between surface and volume reflectance in optical phantoms as well as in breast tissue samples.

In terahertz (THz) spectroscopy water content correlates with the tissue pathological changes. At the same time, water reduces the depth of THz-wave penetration in tissues. In order to unmask cells’ and tissues’ biophysical properties and to increase the tissues probing depth, immersion optical clearing (IOC) was recently introduced in the THz range. For studying common IOC agent’s optical properties in the frequency range of 0.1–2.5 THz, pulsed spectroscopy was used. Diffusion coefficients of IOC agents in ex vivo rat brain tissue were studied using the collimated transmission spectroscopy in the visible range. Two-dimensional nomogram was used to objectively compare IOC agents, based on their THz-wave absorption coefficients and diffusion rates.

Our group recently published direct observation of membrane charging in FluoVolt labeled CHO-K1 cells by nanosecond electrical pulses using a streak camera. Using this technique, called Streak Camera Microscopy (SCM), we imaged the membrane charging dynamics in giant unilamellar vesicles (GUVs) during AC exposures up to 6 MHz and compared these results to existing capacitive circuit models of membranes. This work shows further application of Streak Camera Microscopy for evaluation of high speed biological events.

Astrocytes play a critical role in regulating brain physiology at ionic, synaptic and whole-organ level. Their function is mainly controlled by ionic signalings, in particular Ca2+ signaling, that mediate cell-cell communication. Infrared pulsed stimulation is a label-free tool that has been previously used to modulate neuronal firing. Here we present the use of infrared pulsed light to stimulate ionic astrocytic signaling in order to modulate astroglial physiology. We present infrared pulsed stimulation as a powerful technique to understand astrocytic function and dysfunction.

Photodynamic therapy is a treatment technique that takes advantage of the effects induced by the body itself, together with a photosensitizer, to destroy unwanted tumor volumes with high accuracy and low invasiveness. This study analyzes treatment volume by 3D optical distributions in a realistic way from MRI images. First of all a volumetric model of a real head is built from MRI images. Optical distributions generated by the source over the tissue are considered at different brain tumor stages, and with multitude of processes that occur within the volume to be treated. By means of Monte Carlo we can estimate the photonic density that is absorbed by the tissues, whose optical properties are previously collected. This application considers that a reasonable time has passed for the photosensitizer to have reached the area under study, and that there is a minimum concentration in adjoining areas during radiation exposure. With this approach it is possible to estimate the level of radiation exposure and the affected volume. This is very relevant due to the fact that, as the radiation increases, different areas with different energy densities appear. This makes it much more complicated to apply a certain known optimal radiation on the treatment volume. A non-optimal high radiation density would damage healthy tissue, while, on the contrary, a non-optimal low radiation would not bring unwanted tissue to necrosis or apoptosis for tumor destruction, generating recurrence. This tool could be of great interest in treatment planning.

The fields of photodynamic therapy (PDT) and radiation therapy customarily rely on lasers operating at a fixed wavelength (typically 1064 nm Nd:YAG laser), primarily because of the traditional availability of such lasers. However, Raman fiber lasers have made concurrent technological progress to emerge as wavelength-agile laser sources, capable of providing high laser powers at any wavelength, primarily from the 1 -2.0 um wavelengths. In this work, we explore for the first time, the use of a high power, wavelength-tunable Raman fiber laser for performing a wavelength-dependent cell-killing effect study on cancerous and healthy cell lines. Specifically, we irradiate at different wavelengths (from 1 um to 1.6 um) breast cancer cells and healthy cells from a cell line, cultured in well plates. Our in-house built Raman laser is power-tunable apart from being wavelength-tunable, the power and duration of irradiation was optimised for achieving the best contrast between viability of cancerous vs. healthy cells. Flow cytometry is used for cell-viability tests. The results give interesting insights on the choice of wavelengths and we show that 1064 nm lasers traditionally used are not the best choice of wavelength to use for this application while 1480nm lasers performed best. We conclusively demonstrate that other wavelengths exist for achieving the best death rate in cancerous cells, leaving healthy cells unharmed. This can pave the way for deployment of Raman fiber lasers as an alternative laser source for this application which can tune the output wavelength to optimize the required laser tissue interaction. For the keywords, select up to 8 key terms for a search on your manuscript's subject.

We present here an open-source platform capable of simulating Optical Coherence Tomography (OCT) images to be used by the community. Such a simulator can have a variety of applications such as the training of neural networks. Our first-generation Monte Carlo simulator quantifies detected photons path length. The code achieves reasonable runtime by exploiting a bias scattering scheme. The results are then interpreted to produce an OCT A-line. A Github platform was implemented with necessary documentation (e.g. readme file and instructions guide) to allow a variety of application and geometry as well as community-based improvements over time.

In the context of cutaneous carcinoma in vivo diagnosis, Diffuse Relectance (DR) acquired using Spatially Resolved (SR) optical biopsy, can be analysed to discard healthy from pathological areas. Indeed, carcinogenesis induces local morphological and metabolic changes affecting the skin optical answer to white light excitation. The present contribution aims at studying the epidermis thickness impact on the path and propagation depth distribution of DR photons in skin in the perspective of analyzing how these photons contribute to the corresponding acquired spectra carrying local physiological information from the visited layers. Modified CudaMCML-based simulations were performed on a five-layer human skin optical model using (i) wavelength-resolved scattering and absorption properties and (ii) the geometrical configuration of a multi-optical fiber probe implemented on a SR-DR spectroscopic device currently used in clinics. Through maps of scattering events and histograms of maximum probed depth, we provide numerical evidences linking the characteristic penetration depth of the detected photons to their wavelengths and four source-sensor distances for thin, intermediate and wide skin thicknesses model. The study provides qualitative and quantitative tools that can be useful during the design of an optical SR-DR spectroscopy biopsy device.

Biomedical optical techniques of treatment, characterization and surgery depend on light propagation in biological tissues. As biological tissues are turbid media it is necessary to adequately analyze its influence on optical propagation parameters, such as coherence. The influence of a scatterers distribution can be analyzed using Green's functions. Green's functions are sets of impulse responses of inverse operators of differential linear operators with homogeneous boundary conditions. Optical random beams, mainly Gaussian-based, are employed to model light propagation in turbid biological tissues by Green’s functions. Enhanced contrast by coherence could distinguish malignant from healthy tissues or provide diagnostic interpretation.

For some time now, the diode-pumped Er:YAG laser (Pantec Biosolutions AG) has been available. Due to its high repetition rate of up to 2 kHz, it shows an excellent cutting quality and efficiency in soft tissue. Now, due to the novel special pulse regime, significantly longer effective pulse duration and higher pulse energy of up to 1.5 J is available. The aim of the present study was to evaluate the ablation quality, efficiency and thermal side effects of the new pulse regime. For this purpose, in-vitro experiments were performed on slices of teeth and pig bones with varying laser irradiation parameters. The laser beam was coupled into a sapphire fiber and the fiber end was imaged onto an 800 µm spot on the sample. The sample was shifted with a computer-aided movement unit at different speeds during irradiation. A water spray with 6 ml/min was used for moistening. After irradiation, the resulted ablation quality was recorded under the light microscope and the ablation depth and width were measured. The ablation efficiency in super pulse mode is comparable on enamel and exceeds the values in dentin for standard pulse mode. The maximum ablation efficiency on bone is 0.20 mm³/J and is on average approx. 18,2% above the values achieved in standard operation. The ablation quality and the thermal injury achieved with the novel pulse regime is comparable to the results obtained with the standard operation of the diode-pumped Er:YAG laser. Overall, the tests show that the diode-pumped Er:YAG laser with the novel pulse regime and higher effective pulse energy allows larger spot size and with this more homogeneous ablation.

Obesity is a significant risk factor for development and management of cardiovascular disease, one of the leading causes of death in the United States. Blood pressure (BP) is a key factor for monitoring cardiac health. In support of design and development of wearable health devices, we have developed a model to generate synthetic photoplethysmographic waveforms captured by a commercial device for the radial artery at the volar surface of the wrist. We focus on impacts to the PPG signal as a result of various changes attributed to obesity, epidermal melanin, and vascular layers.

A new method of treating open-angle glaucoma is proposed. The concept of non-stationary thermo-mechanical stress under laser radiation in the wavelength range 1000-1600 nm in the structural elements of the anterior segment of the eye is developed. The solution of the problem of forced vibrations of a viscoelastic medium showed that a significant part of the cavitation pores formed in the negative phase of the laser-wave is stable and does not collapse with increasing pressure. The results of clinical studies have shown the stability of the laser-induced hypotensive effect over four years of follow-up.

The purpose of this study is to obtain the relationship between skin absorbance, a rise in temperature on the skin surface, and skin burns in several mammalian species and to estimate burn risk in humans. We measured the skin absorbance of the species by diffuse reflectance spectroscopy and applied a near-infrared pulsed laser to each species on their skin. Laser irradiation raised temperature on the skin surface and caused skin burns in areas with higher absorbance, regardless of the species. We estimated the risk of skin burns for each skin type by comparing skin absorbance between humans and the mammals.

Human keratinocytes were exposed to continuous wave 900 MHz RF field for 60 minutes. High-throughput RNA sequencing was used to examine global changes in gene expression and differentially expressed genes (DEGs) were defined as having adjusted p value ≤ 0.05 and absolute fold change ≥ 1.3. We used gene enrichment analysis and functional annotation clustering via DAVID Bioinformatics Resources to analyze pathways and gene sets enriched in DEGs. Numerous gene sets related to keratinocyte differentiation and development were enriched in the RF exposed cells.

We have computed effective specific absorption rate (SAR) and change in the temperature for a four-layered human-head model when exposed to electromagnetic radiations from a common antenna in mobile phones. Human head is modeled as having four layers of skin, fat, bone, and brain. A realistically shaped human-head model is used in contrast to an oval-shaped model. The SAR and change in temperature is computed as a function of the distance of the antenna from the head at 900 and 1200 MHz. It was found that increasing the distance of the antenna from the head from 1 to 2 cm can significantly decrease the absorbed power in different tissues.

Photoacoustic microscopy (PAM) is a promising biomedical imaging technique that relies on sequential excitation to generate three-dimensional images. It combines the high contrast of optical imaging with high penetration depth of ultrasound imaging. The normal respiration rate of mice is greater than 3 Hz, which leads to motion artifacts in most reported PAM for in-vivo imaging. Here, we introduce a prospective respiratory gating (PRG) method for photoacoustic microscopy to address this problem. We captured the mouse’s respiratory signal with a laser displacement sensor, when the detector detects a respiratory trough, the stage moves a certain number of positions and sends a corresponding number of pulses to trigger the laser light and the data acquisition. The stage will only move during the nadir of respiration, and the movement also must stop before the next respiration peak. We combined this method with our PAM to demonstrate its feasibility. A series of experiments were performed to verify the feasibility of this technology. The carbon fiber attached to the abdomen of mouse was visualized to quantify the performance of the PRG. The subcutaneous vascular imaging results of the mouse abdominal region with PRG are much better than those without any gating. Our experiments show that the proposed method can help to remove motion artifacts well.