A new four channel continuous wave near IR spectroscopy instrument for regional cerebral oxygenation monitoring has been developed. The instrument uses laser diodes to transmit pulses of near IR light at wavelengths of 775, 845 and 904 nm. The instrument incorporates an optical switching mechanism that switches transmitted and received light in turn to monitor four regions in a time period of 4 seconds. The stability and linearity of the instrument have been measured and indicate satisfactory performance of the system. Initial tissue phantom experiments with a scattering solution of $mu$-s$/' estimated at 0.5mm$+$MIN@1$/ and black absorbing spheres of varying diameter embedded in the solution, were conducted to assess the capability of the instrument to differentiate between regional changes. These experiments involved moving the position of the transmitting and receiving fibers with respect to the spheres and observing the change in attenuation of the light intensity of the four regions. The results showed that the location of the absorber could be detected regionally. Results were also obtained form adult human forearm venous and arterial occlusions for 8 subjects. The forearm was chosen because the presence of two bones, the radius and the ulna, should create differences in regional measurements. Good correlation for percentage of venous oxygen saturation was observed in 7 of the subjects. Expected decreases in oxygenated hemoglobin and increases in deoxygenated hemoglobin were observed in 7 subjects after the application of arterial occlusions.
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