Development of a theory of the spectral reflectance of minerals, part 2

Theory of diffuse reflectance of particulate media including garnet, glass, corundum powders, and mixture

Diffuse reflectance measurement tool for laparoscopic surgery

Continuous-wave diffuse reflectance or Near Infrared Spectroscopy (NIRS) offers the possibility to perform a preliminary screening of tissue for ischemia or other tissue anomalies. A tool for intracavity NIRS measurements during laparoscopic surgery, developed within the framework of the FP7-IP ARAKNES (Array of Robots Augmenting the KiNematics of Endoluminal Surgery) project, is described. It consists of a probe, that is located on the tip of an appropriately shaped laparoscopic manipulator and then applied to the tissue. Such a probe employs an array of incoherent semiconductor light sources (LEDs) frequency-multiplexed on a single detector using a lock-in technique. The resulting overall tool structure is simple and compact, and allows efficient coupling of the emitted light towards the tissue. The tool has high responsivity and enables fast and accurate measurements. A dataset gathered from in-vivo tissue is presented. The performance both indicates direct applicability of the tool to significant surgical issues (ischemia detection), and clearly indicates the possibility of further miniaturizing the probe head towards catheterized approaches

Micromachined “side-viewing” optical sensor probe for detection of esophageal cancers

In this paper, we report the design, fabrication and testing of a new miniaturized optical sensor probe with “side viewing” capability for oblique incidence diffuse reflectance spectrometry. The sensor probe consists of a lithographically patterned polymer waveguides chip and two micromachined positioning substrates and source/collection fibers to achieve 45° light incidence and collection of spatially resolved diffuse reflectance. Diffuse reflectance of human esophageal surface has been successfully measured for differentiation of cancerous tissues from normal ones

Oblique-incidence reflectometry: one relative profile measurement of diffuse reflectance yields two optical parameters

A new, simple and quick approach, oblique-incidence reflectometry, was used to measure the absorption and reduced scattering coefficients of a semi-infinite turbid medium. An obliquely incident light beam causes the center of the far diffuse reflectance to shift from the point of incidence, where the far diffuse reflectance refers to the diffuse reflectance that is several transport mean free paths away from the incident point. The amount of shift yields the diffusion constant by a simple formula, and the slope of the diffuse reflectance yields the attenuation coefficient. Only the relative profile of the diffuse reflectance is needed to deduce both optical parameters, which makes this method attractive in clinical settings because it does not require a stringent calibration for absolute quantity measurements. This method was tested theoretically by Monte Carlo simulations and experimentally by a reflectometer. Because this method can be used to measure optical properties of biological tissues quickly and requires only inexpensive equipment, it has potential clinical application to the diagnosis of disease or monitoring of treatments

Oblique incidence reflectometry: optical-fiber implementation

A new, simple and quick approach, oblique-incidence reflectometry, was used to measure the absorption and reduced scattering coefficients of a semi-infinite turbid medium. An obliquely incident light beam causes the center of the far diffuse reflectance to shift from the point of incidence, where the far diffuse reflectance refers to the diffuse reflectance that is several transport mean free paths away from the incident point. The amount of shift yields the diffusion constant by a simple formula, and the slope of the diffuse reflectance yields the attenuation coefficient. Only the relative profile of the diffuse reflectance is needed to deduce both optical parameters, which makes this method attractive in clinical settings because it does not require a stringent calibration for absolute quantity measurements. This method was tested theoretically by Monte Carlo simulations and experimentally by a reflectometer. Because this method can be used to measure optical properties of biological tissues quickly and requires on inexpensive equipment, it has potential clinical application to the diagnosis of disease or monitoring of treatments

Indigo in the nanochannels of zeolite L : towards a new type of colorant

A host-guest based colorant was synthesized by intercalating indigo molecules into the nanochannels of zeolite L (ZL). Reductive washing thereby ensured the efficient and selective removal of non-intercalated indigo molecules. The UV-vis diffuse reflectance spectrum of the product after intercalation and reductive washing (designated as indigo-ZL) was found to resemble the solution spectrum of indigo, leading to the conclusion that the formation of indigo aggregates is prevented due to the steric constraints imposed by the microporous structure of ZL. The application of indigo-ZL on cotton was tested by roll coating. The light absorption properties of the resulting textile prints showed no significant alteration when compared to the pure indigo-ZL powder. The UV-vis diffuse reflectance spectra of mixtures consisting of indigo-ZL and a further ZL-based colorant were successfully predicted by the weighted addition of the respective primary spectra

Modeling diffuse reflectance from homogeneous semi-infinite turbid media for biological tissue applications: a Monte Carlo study

Diffuse reflectance spectroscopy is one of the simplest and widely used techniques for the non-invasive study of biological tissues but no exact analytical solution exists for the problem of diffuse reflectance from turbid media such as biological tissues. In this work, a general treatment of the problem of diffuse reflectance from a homogeneous semi-infinite turbid medium is presented using Monte Carlo simulations. Based on the results of the Monte Carlo method, simple semi-empirical analytical solutions are developed valid for a wide range of collection geometries corresponding to various optical detector diameters. This approach may be useful for the quick and accurate modeling of diffuse reflectance from tissues

Diffuse reflectance of foams

There have been few studies of the optical properties of foams but the results of these investigations are of particular relevance to current discussions about climate restoration by means of oceanic foam because they indicate the influence of foam raft number on albedo. The diffuse reflectance of foams prepared from eight surfactants was measured in a 0°/45° geometry with a collimated, solar simulation light source and a photodiode by reference to barium sulphate white standards. Reflectance, or albedo, in the range of 0.5 to 0.59 was recorded for foams prepared with sodium dodecyl sulphate (SDS), methyl cellulose, and TWEEN 20TM. Perfluoro-surfactants produced more stable foams with reflectance over 60%. The apparatus was adjusted to the 45°/45° configuration (specular reflection) and used to test the suggestion that a foam can be treated, for purpose of approximation, as a series of horizontal planar reflective layers in which reflectance reaches a limiting value. The resulting geometric series, when summed over an infinite number of layers yields an albedo of 0.62 to 0.65 when the reflectance of individual layers of which the model is comprised was varied over the range 0.01 to 0.1 respectively. This was tested experimentally using eight sheets of 500 μm thick glass separated by 18 μm thick glass cover slides in 45°/45° mode and the results agreed to within less than 9% with the model calculation. The insensitivity to layer reflectance and the fact that limiting reflectance for the assembly is reached after about 20 layers provides a simple working model to assess the dependence of reflectance on thickness and cell diameter

Method of Predicting Cut-Time of Milk Coagulum in Cheese-Making Process

An apparatus for predicting milk coagulum cut-time in a cheese making process includes a light source, a sensor or detector for sensing diffuse reflectance of light from said milk and a controller for analyzing the diffuse reflectance and accurately predicting the cut-time to significantly enhance overall yield. More specifically, the apparatus includes an optical probe which may be suspended over the milk or attached to a wall of a fermentation vessel in which the milk is contained. A method for predicting milk coagulum cut-time includes the steps of (a) directing light from a light source toward milk undergoing enzymatic hydrolysis; (b) sensing diffuse reflectance of that light from the milk; (c) analyzing the sensed diffuse reflectance profile and (d) signaling the cut-time. The sensing occurs at between 400 to 6000 nm. Specific mathematical formulae for the analyzing steps are also disclosed

Depth resolved diffuse reflectance spectroscopy

textThis dissertation focuses on the development of computational models and algorithms related to diffuse reflectance spectroscopy. Specifically, this work aims to advance diffuse reflectance spectroscopy to a technique that is capable of measuring depth dependent properties in tissue. First, we introduce the Monte Carlo lookup table (MCLUT) method for extracting optical properties from diffuse reflectance spectra. Next, we extend this method to a two-layer tissue geometry so that it can extract depth dependent properties in tissue. We then develop a computational model that relates photon sampling depth to optical properties and probe geometry. This model can be used to aid in design of application specific diffuse reflectance probes. In order to provide justification for using a two-layer model for extracting tissue properties, we show that the use of a one-layer model can lead to significant errors in the extracted optical properties. Lastly, we use our two-layer MCLUT model and a probe that was designed based on our sampling depth model to extract tissue properties from the skin of 80 subjects at 5 anatomical locations. The results agree with previously published values for skin properties and show that can diffuse reflectance spectroscopy can be used to measured depth dependent properties in tissue.Biomedical Engineerin