Near-ir light (700-900) penetrates several centimeters into tissues and passes through bony structure and fat layers. The major contribution to light absorption in this spectral region arises from hemoglobin. In response to tissue metabolism, the hemoglobin oxygenation and its spectral properties changes and the hemoglobin concentration increases. During the previous granting period, we developed frequency-domain methods that allowed us to precisely quantify tissue oxygenation changes, in conjunction with measurements at different locations on the tissue surface. High-frequency (approximately modulated light is applied to a part of the tissue using optical fibers and then collected at different locations, generally 3-4 cm from the source, after the his diffused deep into the tissue. The determination of the tissue optical properties was very fast and suggested the possibility of performing junctional studies in the brain and the muscles that were not available before. One apparent limitation of the use of the diffusive part of the light that propagates in tissues is the relatively low spatial resolution (about 1 cm). However, our research shows that if we observe changes of tissue optical parameters, then the spatial and temporal resolution can be greatly improve with respect to steady-stage measurements. In this application, we propose to develop a new detector for the study of rapid changes (1 to 10 ms time scale) of optical parameters deep (1 to 2 cm) in tissues. The new detector can localize changes occurring in a small volume (3 mm in radius). It has low noise nd relatively high bandwidth. Using this new detector we will study the dynamics of tissues, particularly the muscle and the rain in the frequency bandwidth up to 100 Hz. Our approach signals a significant advance with respect to current methodologies and this method will provide physiologists with a new tool for functional studies of the brain and other tissues.
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