Development of a Hyperspectral FD-NIRS Device for Muscle Physiology

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ABSTRACT Near-infrared spectroscopy (NIRS) is a non-invasive optical technique to measure chromophore concentrations in tissue including hemoglobin, myoglobin, water, lipid, and cytochrome C oxidase. Continuous wave (CW-) NIRS systems are widely used but are limited to the measurement of changes in chromophore concentrations and have low quantitative accuracy in reporting absolute concentrations due to the unknown pathlength factors related to the diffusion of light in tissue. Frequency-domain (FD-) NIRS is a variation of this method that uses amplitude modulated light and the measurement of the amplitude and phase of the light passing through tissue to provide more quantitative estimates of baseline optical properties. However, current FD-NIRS systems are limited to only a few optical wavelengths due to the cost and complexity of these modulation circuits. In this project, we propose to develop a novel hyperspectral FD-NIRS system, which uses a broadband white light source and CCD spectrometer detection system. The unique innovation of this system is the use of electro-optical modulators (EOMs), which will be used to directly modulate the light rather than relying on electrical modulation of laser diodes. Two devices will be used to enable heterodyne downshifting of these MHz signals for CCD detection. This approach will be a much simpler and more cost effective way to increase the number and range of wavelengths used by the system in comparison to previous versions of CW- and FD-NIRS systems. This device will improve the way in which NIRS is collected across a wide range of applications. The aims of this study are: Aim 1. Construct a hyperspectral FD-NIRS device and characterize sensitivity and noise properties of the instrument. Aim 2. Investigate the sensitivity and specificity of CW- and FD-NIRS measurements in simulated muscle tissue using Monte Carlo techniques to look at the effect of realistic muscle structure on photon migration. Aim 3. Characterize the sensitivity and specificity of the measurement of physiological compounds using the device in phantoms and compare with Monte Carlo simulation results. This proposed R03 study will develop this unique system and allow us to apply these advanced NIRS techniques in future studies of muscle physiology including injury risk assessment, the impact of aging and diabetes, among various other work.