Mr. Par Hjalmarsson Profile

Par Hjalmarsson

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Proceedings Article | 6 February 2008 Paper

Determination of glucose concentration in tissue-like material using spatially resolved steady-state diffuse reflectance spectroscopy

Pär Hjalmarsson, Suresh Thennadil

Proceedings Volume 6855, 685508 (2008) https://doi.org/10.1117/12.762279

KEYWORDS: Glucose, Tissue optics, Absorption, Scattering, Diffuse reflectance spectroscopy, Monte Carlo methods, Calibration, Sensors, Tissues, Optical properties

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An important parameter in medical diagnostic and one of the most frequently determined analyte in the hospitals is blood glucose. Fast and accurate methods of measuring blood glucose concentrations could therefore be significant. We will in this paper investigate the feasibility of using a spatially resolved steady-state diffuse reflectance spectroscopy in the wavelength region 1000-1700nm, where glucose has two absorption peaks at around 1250nm and 1600nm, to quickly determine the concentration of glucose in tissue-like material. This method could later be transferred to estimate the amount of glucose in blood both in vivo e.g. the forearm and in vitro e.g. on blood samples. The novel spatially resolved system that is used for this study is based around a 2D InGaAs detector and a fibre probe with 10 fibres, one as a source and 9 to collect the diffuse reflected light at distances between 0.3-2.7mm from the source. An inversion method using Monte Carlo generated diffuse reflectance profiles is used to estimate the absolute absorption coefficient (μ_a) and reduced scattering coefficient (μ_s') which could be used to estimate the glucose concentration in the tissue-like phantoms. The method was investigated by performing spatially resolved measurements on turbid gelatin phantoms containing mixtures of water and D₂O as absorbers, Intralipid as a scatterer and glucose. The phantoms were made with four different glucose concentrations spanning the range of 0-5000 mg/dl.

Proceedings Article | 19 July 2007 Paper

Spatially resolved in vivo measurement system for estimating the optical properties of tissue in the wavelength range 1000-1700 nm

Pär Hjalmarsson, Suresh Thennadil

Proceedings Volume 6628, 662805 (2007) https://doi.org/10.1117/12.728183

KEYWORDS: Optical properties, Monte Carlo methods, Tissue optics, Sensors, Absorption, Diffuse reflectance spectroscopy, Scattering, Integrating spheres, Reflectivity, Calibration

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For non-invasive estimation of optical properties (i.e. determination of the absorption and the reduced scattering coefficients) of turbid media such as tissue, spatially resolved diffuse reflectance spectroscopy is one of most used technique. So far this has only been done for wavelengths covered by CCD-detectors (about 350-1050nm). The NIR region beyond 1050nm i.e. the second and first overtone regions, has absorption peaks of interest e.g. for tissue the glucose peak at around 1250nm and 1600nm. Thus for non-invasive medical diagnostics applications, a spatially resolved measurement system capable of estimating optical properties in this region will be very useful. Until now optical properties of tissue in this region have only been estimated using in vitro methods e.g. using an integrating sphere set-up. In this paper we describe a spatially resolved system that will extend the region up to 1700nm by using a TE cooled 320×256 pixel InGaAS detector, a white light source and a probe that consists of 9×200micron fibres spanning 0.3 to 2.7mm from the source. Across the 320 pixels 680nm will be dispersed giving a resolution of 2.125nm/pixel and a resolving power of about 14nm. The system is validated using tissue-like phantoms. Since tissue has a high concentration of water which leads to high absorption after 950nm, the diffusion approximation cannot be used to extract the optical properties from the spatially resolved measurements. Instead, two techniques based around Monte Carlo simulations of diffuse reflectance profiles, to build a lookup table coupled with interpolation using splines or a third order polynomial, have been used to calculate the optical properties for different wavelengths. The performances of these techniques are compared. It was found that the spline fitting produced lower error for the wavelength region considered.

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