Photoplethysmography (PPG) is a low-cost, noninvasive optical technique that uses change in light transmission with changes in blood volume within tissue to provide information for cardiovascular ...health and fitness. As remote health and wearable medical devices become more prevalent, PPG devices are being developed as part of wearable systems to monitor parameters such as heart rate (HR) that do not require complex analysis of the PPG waveform. However, complex analyses of the PPG waveform yield valuable clinical information, such as: blood pressure, respiratory information, sympathetic nervous system activity, and heart rate variability. Systems aiming to derive such complex parameters do not always account for realistic sources of noise, as testing is performed within controlled parameter spaces. A wearable monitoring tool to be used beyond fitness and heart rate must account for noise sources originating from individual patient variations (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to the skin). Here, we present a comprehensive review of the literature that aims to summarize these noise sources for future PPG device development for use in health monitoring.
Dyspigmented hypertrophic scars: Beyond skin color Alkhalil, Abdulnaser; Carney, Bonnie C.; Travis, Taryn E. ...
Pigment cell and melanoma research,
September 2019, Letnik:
32, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Although pigment synthesis is well understood, relevant mechanisms of psychologically debilitating dyspigmentation in nascent tissue after cutaneous injuries are still unknown. Here, differences in ...genomic transcription of hyper‐ and hypopigmented tissue relative to uninjured skin were investigated using a red Duroc swine scar model. Transcription profiles differed based on pigmentation phenotypes with a trend of more upregulation or downregulation in hyper‐ or hypopigmented scars, respectively. Ingenuity Pathway Analysis of significantly modulated genes in both pigmentation phenotypes showed pathways related to redox, metabolic, and inflammatory responses were more present in hypopigmented samples, while those related to stem cell development differentiation were found mainly in hyperpigmented samples. Cell–cell and cell–extracellular matrix interactions and inflammation responses were predicted (z‐score) active in hyperpigmented and inactive in hypopigmented. The proinflammatory high‐mobility group box 1 pathway showed the opposite trend. Analysis of differentially regulated mutually exclusive genes showed an extensive presence of metabolic, proinflammatory, and oxidative stress pathways in hypopigmented scars, while melanin synthesis, glycosaminoglycans biosynthesis, and cell differentiation pathways were predominant in hyperpigmented scar. Several potential therapeutic gene targets have been identified.
Cardiovascular disease is one of the leading causes of death in the United States and obesity significantly increases the risk of cardiovascular disease. The measurement of blood pressure (BP) is ...critical in monitoring and managing cardiovascular disease hence new wearable devices are being developed to make BP more accessible to physicians and patients. Several wearables utilize photoplethysmography from the wrist vasculature to derive BP assessment although many of these devices are still at the experimental stage. With the ultimate goal of supporting instrument development, we have developed a model of the photoplethysmographic waveform derived from the radial artery at the volar surface of the wrist. To do so we have utilized the relation between vessel biomechanics through Finite Element Method and Monte Carlo light transport model. The model shows similar features to that seen in PPG waveform captured using an off the shelf device. We observe the influence of body mass index on the PPG signal. A degradation the PPG signal of up to 40% in AC to DC signal ratio was thus observed.
Calibration, quantification, and standardization of the polarimetric instrumentation, as well as interpretation and understanding of the obtained data, require the development and use of ...well-calibrated phantoms and standards. We reviewed the status of tissue phantoms for a variety of applications in polarimetry; more than 500 papers are considered. We divided the phantoms into five groups according to their origin (biological/nonbiological) and fundamental polarimetric properties of retardation, depolarization, and diattenuation. We found that, while biological media are generally depolarizing, retarding, and diattenuating, only one of all the phantoms reviewed incorporated all these properties, and few considered at least combined retardation and depolarization. Samples derived from biological tissue, such as tendon and muscle, remain extremely popular to quickly ascertain a polarimetric system, but do not provide quantifiable results aside from relative direction of their principal optical axis. Microspheres suspensions are the most utilized phantoms for depolarization, and combined with theoretical models can offer true quantification of depolarization or degree of polarization. There is a real paucity of birefringent phantoms despite the retardance being one of the most interesting parameters measurable with polarization techniques. Therefore, future work should be directed at generating truly reliable and repeatable phantoms for this metric determination. Diattenuating phantoms are rare and application-specific. Given that diattenuation is considered to be low in most biological tissues, the lack of such phantoms is seen as less problematic. The heterogeneity of the phantoms reviewed points to a critical need for standardization in this field. Ultimately, all research groups involved in polarimetric studies and instruments development would benefit from sharing a limited set of standardized polarimetric phantoms, as is done earlier in the round robin investigations in ellipsometry.
Reflectance Mueller matrix (MM) polarimetry is being used to characterize biological media in multiple clinical applications. The origin of the reflectance polarimetric data is often unclear due to ...the impact of multiple scattering and tissue heterogeneity. We have developed a new, to the best of our knowledge, multimodal imaging technique combining MM reflectance, MM digital confocal imaging, and co-registered nonlinear microscopy techniques. The instrument unveils the origin of reflectance polarimetric signature in terms of confocal reflectance data. The reconstructed reflected MM demonstrates the capability of our method to provide depth-resolved 3D polarization response from complex biological media in terms of depolarization, retardance, and orientation parameters.
The ability to phenotype wounds for the purposes of assessing severity, healing potential and treatment is an important function of evidence‐based medicine. A variety of optical technologies are ...currently in development for noninvasive wound assessment. To varying extents, these optical technologies have the potential to supplement traditional clinical wound evaluation and research, by providing detailed information regarding skin components imperceptible to visual inspection. These assessments are achieved through quantitative optical analysis of tissue characteristics including blood flow, collagen remodeling, hemoglobin content, inflammation, temperature, vascular structure, and water content. Technologies that have, to this date, been applied to wound assessment include: near infrared imaging, thermal imaging, optical coherence tomography, orthogonal polarization spectral imaging, fluorescence imaging, laser Doppler imaging, microscopy, spatial frequency domain imaging, photoacoustic detection, and spectral/hyperspectral imaging. We present a review of the technologies in use or development for these purposes with three aims: (1) providing basic explanations of imaging technology concepts, (2) reviewing the wound imaging literature, and (3) providing insight into areas for further application and exploration. Noninvasive imaging is a promising advancement in wound assessment and all technologies require further validation.
Significance: Monte Carlo (MC) methods have been applied for studying interactions between polarized light and biological tissues, but most existing MC codes supporting polarization modeling can only ...simulate homogeneous or multi-layered domains, resulting in approximations when handling realistic tissue structures.
Aim: Over the past decade, the speed of MC simulations has seen dramatic improvement with massively parallel computing techniques. Developing hardware-accelerated MC simulation algorithms that can accurately model polarized light inside three-dimensional (3D) heterogeneous tissues can greatly expand the utility of polarization in biophotonics applications.
Approach: Here, we report a highly efficient polarized MC algorithm capable of modeling arbitrarily complex media defined over a voxelated domain. Each voxel of the domain can be associated with spherical scatters of various radii and densities. The Stokes vector of each simulated photon packet is updated through photon propagation, creating spatially resolved polarization measurements over the detectors or domain surface.
Results: We have implemented this algorithm in our widely disseminated MC simulator, Monte Carlo eXtreme (MCX). It is validated by comparing with a reference central-processing-unit-based simulator in both homogeneous and layered domains, showing excellent agreement and a 931-fold speedup.
Conclusion: The polarization-enabled MCX offers biophotonics community an efficient tool to explore polarized light in bio-tissues, and is freely available at http://mcx.space/.
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