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Theoretical analysis of crosstalk between oxygenated and deoxygenated haemoglobin in focal brain-activation measurements by near-infrared topography

Kawaguchi H., Okui N., Sakaguchi K., Okada E.

Opto-Electronics Review

2008

Vol. 16, No. 4

404-412

The crosstalk between concentration changes in oxygenated haemoglobin and deoxygenated haemoglobin calculated by the modified Lambert-Beer law in near-infrared topography is theoretically investigated. The changes in intensity detected with probe pairs on the scalp caused by the concentration change in either oxygenated or deoxygenated haemoglobin induced by the focal brain activation is predicted by Monte Carlo simulation. The topographic images of the changes in oxygenated and deoxygenated haemoglobin are obtained from the changes in the intensity of light at two wavelengths detected by probe pairs to evaluate the crosstalk. The crosstalk slightly depends on the positional relationship between the probe arrangement and the focal brain activation and is minimised when the focal brain activation is located below a measurement point that is the midpoint between a probe pair. The 690-/830-nm wavelength pair is practically effective for reducing the crosstalk, especially the crosstalk from oxygenated haemoglobin to deoxygenated haemoglobin, in the NIR topography.

Modelling of light propagation in the adult head for optical brain function mesurement

Okada E.

Biocybernetics and Biomedical Engineering

2002

Vol. 22, no. 4

135-147

Near infrared (NIR) spectroscopy and imaging are now established techniques for measurements of change in oxygenation and haemo-dynamics within the brain. However, scattering of the light in biological tissue causes ambiguity in the spatial sensitivity profiles and the partial optical path lenght in the brain. The light propagation in the adult head model of which optical properties are chosen from the reported data of in vitro experiments is validated by time-resolved measurements of the human foreheads. The apparent optical properties estimated by a least squares fit of the diffusion model to the temporal point spread function for the adult head model agree with the experimental results. The heterogeneity of the head scarcely affects the total optical path lenght. However the partial optical path lenght in the brain and the spatial sensitivity profiles which can not be directly obtained by experiment are considerably affected by the heterogeneity of tissue, especially the presence of low scattering subarachnoid space surrounding the brain.