New cross-talk measure of near-infrared spectroscopy and its application to wavelength combination optimization

In near-infrared spectroscopy, concentration changes in oxygenated and deoxygenated hemoglobin are calculated from the changes in the attenuation of the measurement light. This is done by solving a linear equation based on the modified Lambert-Beer law. To solve this equation, we need to know the partial optical pathlengths in the activated region in the brain. Because they are difficult to know, a wavelength-independent constant or a wavelength-dependent total optical pathlength has been substituted for these values in actual measurements. This kind of substitution inevitably produces errors, called cross-talk, when calculating concentration changes. In this paper, we propose a new cross-talk measure for dual and triple wavelength measurements, and analyze it over various wavelength combinations. The results indicate that constant substitution is not inferior to total pathlength substitution in dual wavelength measurements, and that total path-length substitution is very effective for triple wavelength measurements. (C) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3147402]