A time-resolved optical instrument allowing for noninvasive assessment of cerebral oxygenation is presented. The instrument is equipped with picosecond diode lasers, fast photodetectors, and timecorrelated single photon counting electronics. This technology enables depth-resolved estimation of changes in absorption and, in consequence, assessment of changes in hemoglobin concentrations in the brain cortex. Changes in oxyhemoglobin ͑HbO 2 ͒ and deoxyhemoglobin ͑Hb͒ can be evaluated selectively

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... extra-and intracerebral tissue compartments using the moments of distributions of times of flight of photons measured at two wavelengths in the near-infrared region. The combination of the data acquired from multiple sources and detectors located on the surface of the head with the depth-resolved analysis, based on the moments, enables imaging of cortex oxygenation. Results of the tests on physical phantoms as well as in vivo validation of the instrument during the motor stimulation experiment are presented.