An Introduction to Light Interaction with Human Skin

Despite the notable progress in physically-based rendering, there is still a long way to go before one can automatically generate predictable images of organic materials such as human skin. In this tutorial, the main physical and biological aspects involved in the processes of propagation and absorption of light by skin tissues are examined. These processes affect not only skin appearance, but also its health. For this reason, they have also been the object of study in biomedical research. The models of light interaction with human skin developed by the biomedical community are mainly aimed at the simulation of skin spectral properties which are used to determine the concentration and distribution of various substances. In computer graphics, the focus has been on the simulation of light scattering properties that affect skin appearance. Computer models used to simulate these spectral and scattering properties are described in this tutorial, and their strengths and limitations discussed. Keywords: natural phenomena, biologically and physically-based rendering

Balancing Fidelity and Performance in Iridal Light Transport Simulations Aimed at Interactive Applications

Specific light transport models based on first-principles approaches have been proposed for complex organic materials such as human skin and blood. The driving force behind these efforts has been the high-fidelity reproduction of material appearance attributes without one having to rely on the manipulation of ad hoc parameters. These models, however, are usually considered excessively time consuming for rendering applications requiring interactive rates. In this thesis, we address this open problem with respect to one of the most challenging of these organic materials, namely the human iris. More specifically, we present a framework that consists in the careful configuration of algorithms employed by a biophysically-based iridal light transport model on the CUDA (Compute Unified Device Architecture) parallel computing platform. We then investigate the sensitivity of iridal appearance attributes to key model running parameters, namely spectral resolution and number of sample rays, in order to obtain a practical balance between appearance fidelity and performance on this platform. The results of our investigation indicate that predictive light transport simulations can be effectively employed in the generation of iridal images that are not only believable, but also controlled by biophysically meaningful parameters. Although our investigation is centered at the human iris, we believe that it can be viewed as a proof of concept, and the proposed configuration strategies and parameter space explorations can be employed to obtain similar results for other organic materials

On the Optical Monitoring of Anemia Severity Levels

Anemia is a prevalent medical condition that seriously a ects millions of people all over the world. In many regions, not only its initial detection, but also its monitoring are hindered by the limited access to laboratory facilities. This situation has motivated the development of a wide range of optical de- vices and procedures to assist physicians in these tasks. Although noticeable progress has been achieved in this area, the search for reliable, low-cost and risk-free solutions still continues, and the strengthening of the knowledge base about this disorder and its e ects is essential for the success of these initiatives. In this paper, we contribute to these e orts by closely examining the sensitivity of human skin hyperspectral responses (within and outside the visible region of the light spectrum) to reduced hemoglobin concentrations associated with increasing anemia severity levels. This investigation, which involves skin specimens with distinct biophysical and morphological charac- teristics, is supported by controlled in silico experiments performed using a predictive light transport model and measured data reported in the biomed- ical literature. We also propose a noninvasive procedure to be employed in the monitoring of this condition at the point-of-care

Biologically inspired simulation of livor mortis

We present a biologically motivated livor mortis simulation that is capable of modelling the colouration changes in skin caused by blood pooling after death. Our approach consists of a simulation of post mortem blood dynamics and a layered skin shader that is controlled by the haemoglobin and oxygen levels in blood. The object is represented by a layered data structure made of a triangle mesh for the skin and a tetrahedral mesh on which the blood dynamics are simulated. This allows us to simulate the skin discolouration caused by livor mortis, including early patchy appearance, fixation of hypostasis and pressure induced blanching. We demonstrate our approach on two different models and scenarios and compare the results to real world livor mortis photographic examples

Porous structures for the purification of biopharmaceuticals

This work aimed at the development of a (bio)polymeric monolithic support for biopharmaceuticals purification and/or capture. For that, it was assured that functional groups on its surface were ready to be involved in a plethora of chemical reactions for incorporation of the desired and most suitable ligand. Using cryogelation as preparation method a screening on multiple combinations of materials was performed in order to create a potentially efficient support with the minimal footprint, i.e. a monolithic support with reasonable mechanical properties, highly permeable, biocompatible, ready to use, with gravitational performance and minimal unspecific interactions towards the target molecules, but also biodegradable and produced from renewable materials. For the pre-selection all monoliths were characterized physico-chemically and morphologically; one agarose-based and two chitosan-based monoliths were then subjected to further characterizations before and after their modification with magnetic nanoparticles. These three specimens were finally tested towards adenovirus and the recovery reached 84% for the chitosan-GMA plain monolith prepared at -80°C. Monoliths based on chitosan and PVA were prepared in the presence and absence of magnetic particles, and tested for the isolation of GFP directly from crude cellular extracts. The affinity ligand A4C7 previously selected for GFP purification was synthesized on the monolith. The results indicated that the solid-phase synthesis of the ligand directly onto the monolith might require optimization and that the large pores of the monoliths are unsuitable for the purification of small proteins, such as GFP.project PTDC/EBB-BIO/118317/201

CLBlood: A Cell-Based Light Interaction Model for Human Blood

The development of predictive appearance models for organic tissues is a challenging task due to the inherent complexity of these materials. In this thesis, we closely examine the biophysical processes responsible for the appearance attributes of whole blood, one the most fundamental of these materials. We describe a new appearance model that simulates the mechanisms of light propagation and absorption within the cellular and fluid portions of this specialized tissue. The proposed model employs a comprehensive, and yet flexible first principles approach based on the morphological, optical and biochemical properties of blood cells. This approach allows for environment driven changes in the cells' anatomy and orientation to be appropriately included into the light transport simulations. The correctness and predictive capabilities of the proposed model are quantitatively and qualitatively evaluated through comparisons of modeled results with actual measured data and experimental observations reported in the scientific literature. Its incorporation into rendering systems is illustrated through images of blood samples depicting appearance variations controlled by physiologically meaningful parameters. Besides the contributions to the modeling of material appearance, the research presented in this thesis is also expected to have applications in a wide range of biomedical areas, from optical diagnostics to the visualization and noninvasive imaging of blood-perfused tissues

In Silico Investigation of the Light Transmission Profiles of Sand-Textured Soils

Sand-textured soils are found in a wide range of landscapes, from dune fields to coastal areas. The quantification of light penetration through these soils, particularly considering possible variations in the presence of water in their pore space, is of considerable interest not only for remote sensing applications, but also for agricultural, ecological and geophysical studies. Despite its relevance, however, the literature on this topic is still scarce. Moreover, the available light penetration (transmittance) datasets for these soils are affected by experimental and modeling limitations. These include, for instance, the use of samples with morphological and mineralogical characteristics markedly different from those of naturally occurring sand-textured soils. In the investigation described in this thesis, we demonstrate the importance of properly accounting for the iron oxide contents and grain (particle) distributions of these soils in applied research initiatives linked to their spectral responses, notably in the 400 to 1000 nm region of the light spectrum. In order to overcome the limitations outlined above and strengthen the current knowledge in this area, we employed a predictive simulation platform supported by measured data. This platform has as its central component a first-principles light transport model for particulate materials whose implementation has been substantially enhanced during this work. Thus, using this platform, we were able to perform controlled in silico experiments on selected representative samples of these soils by systematically varying their water content, their thickness and the angle of light incidence. Our findings provide an original multi-faceted assessment, both in terms of spectral and angular dependencies, of the light transmission profiles of dry and wet sand-textured soils

On the Application of Photoacoustic Absorption Spectral Data to the Modeling of Leaf Optical Properties

Due to the importance of plants in the Earth's ecosystem, their photobiological responses have become the subject of extensive research in life sciences. Leaf optical models have been developed to assist in the analysis of remotely sensed data to derive information on leaf biochemistry and anatomy from foliar spectral curves (transmittance and reflectance). In this paper, we investigate the implications of using in vitro pigment absorption spectra to model foliar optical properties in the visible domain. Typically pigment absorption spectra have been determined using light absorption spectroscopy or by applying a data fitting approach. Alternatively, we propose the use of photoacoustic absorption spectroscopy, which despite being available in the literature has not been used in the modeling of foliar optical properties before. We also perform computational experiments in which foliar modeled reflectance and transmittance spectral curves generated using these different absorption data sets are compared with actual measured data. Our findings indicate that the proposed alternative not only allows key pigments to be individually incorporated into the models, which, in turn, increases the predictability of the simulations, but also enables the generation of modeled leaf spectra that are closer approximations to measured leaf spectra than those obtained using absorption data derived from standard absorption spectroscopy procedures

On the Bluish Appearance of Veins

The bluish appearance of veins located immediately beneath the skin has long been a topic of interest for biomedical optics researchers. Despite this interest, a thorough identification of the specific optical processes responsible for this phenomenon remains to be achieved. In this paper, we employ controlled in silico experiments to address this enduring open problem. Our experiments, which are supported by measured data available in the scientific literature, are performed using first-principles models of light interaction with human skin and blood. Using this investigation approach, we quantitatively demonstrate that Rayleigh scattering caused by collagen fibrils present in the papillary dermis, a sublayer of the skin, can play a pivotal role in the bluish appearance of veins as suggested by previous works in this area. Moreover, taking colour perception aspects also into account, we systematically assess the effects of variations in fibril radius and papillary dermis thickness on the coloration of veins under different illuminants. Notably, this assessment indicates that Rayleigh scattering elicited by reticulin fibrils, another type of fibril found in the papillary dermis, is unlikely to significantly contribute to the bluish appearance of veins. By strengthening the current understanding about light attenuation mechanisms affecting the appearance of skin and blood, our investigation contributes for the development of more effective technologies aimed at the noninvasive measurement of the physiological properties of these tissues