Abstract
Near-infrared spectroscopy (NIRS) measures changes in the hemoglobin oxygenation state in the human brain. NIRS has recently started to be used for neuroimaging as well as for clinical monitoring. CW-type NIRS instruments have high temporal resolution and allow prolonged-time and continuous measurements, but they do not provide absolute values of changes in hemoglobin concentrations. In contrast, time-resolved spectroscopy (TRS), which uses short-pulse laser diodes as light sources, makes quantification possible. Quantification is necessary for imaging of brain activity. Recently, a 64-channel time-resolved optical tomographical imaging system (optical CT) and a single-channel TRS instrument have been developed. By the use of this optical CT or combining the single-channel TRS instrument with the multichannel CW-type NIRS instrument, we can obtain topographical images. NIRS is completely noninvasive and does not require strict motion restriction during measurements, unlike PET and fMRI. NIRS will provide a new direction for functional mapping studies.
