We have recently introduced a Dual-Slope (DS) method implemented with Frequency-Domain (FD) NearInfraRed Spectroscopy (NIRS). Its chief advantages are a preferential sensitivity to deeper tissue and the suppression of instrumental artifacts. Thus-far, the work using the DS method has focused on local measurements of tissue hemodynamics. The next step in the development of DS is the measurement of spatially resolved absorption changes of tissue in vivo. To achieve this, we designed a DS imaging array for applications on human tissue. We utilized this array to measure maps of absolute optical properties in human skeletal muscle, and muscle hemodynamics during venous occlusion. In each case, spatial maps were created. The maps of baseline absolute optical properties showed higher scattering in connective tissue and higher absorption in muscle tissue. The analysis of hemodynamics found a greater blood accumulation during venous occlusion in muscle. Overall, muscle hemodynamics were shown to be spatially variable over a large area, suggesting the importance of imaging (as opposed to single-location) measurements. The preliminary data on human subjects with this new DS imaging array pave the way for applications in functional NIRS (fNIRS) for mapping brain activation.
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