Mapping of Optical Pathlength of Human Adult Head at Multi-Wavelengths in Near Infrared Spectroscopy
Measurement of multichannel continuous-wave near-infrared spectroscopy (CW-NIRS) is dependent on the modified Beer-Lambert law, which includes optical pathlength (PL) as an essential parameter. PLs are known to differ across different head regions and different individuals, but the distribution of PLs for the whole head has not been evaluated so far. Thus, using time-resolved near-infrared spectroscopy (TR-NIRS), we measured the optical characteristics including PL, scattering coefficients (μ′s), and absorption coefficients (μa) at three wavelengths (760, 800, 830 nm). Then, we constructed maps of these parameters on the subjects’ head surface. While the PLs in nearby channels are similar, they differ depending on the regions of the head. The PLs in the region above the Sylvian fissure tended to be shorter than those in the other regions at all of the wavelengths. The difference in the distribution of PLs may be attributed to differences in tissue absorption and scattering properties. The current study suggests the importance of considering PL differences in interpreting functional data obtained by CW-NIRS.
KeywordsOccipital Region Hamamatsu Photonic Central Sulcus Language Dominance Optical Pathlength
This work was in part supported by Hamamatsu Photonics K.K. (Hamamatsu, Japan), the Program for Promotion of Basic Research Activities for Innovative Bioscience, Health and Labor Sciences Research Grants, Research on Psychiatric and Neurological Diseases and Mental Health, and grant-in-aids from the Ministry of Education, Culture, Sport, Science, and Technology, Japan (18700625 awarded to MO and 18390404 to ID).We thank Dr. Lester Clowney for proofreading the manuscript.
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