Study on the error in the dynamic spectrum method relative with the pathlength factor as a function of wavelength

Utilizing near-infrared spectroscopy for non-invasive blood component concentration sensing has been a focusing topic in biomedical optics applications. The ease of use, low cost and portability of these methods is a clear advantage over the invasive blood component concentration sensing which is the main sensing method in the clinic application. However, there is no report about any successful non-invasive blood components (except the artery blood oxygen saturation) concentration detection techniques that can meet the requirements of clinic application. One of the most key difficulties is the influence of the individual discrepancy. Dynamic spectrum (DS) is a new measure method of non-invasive blood components concentration sensing presented recently. It can eliminate the individual discrepancy of the tissues except the pulsatile component of the artery blood (PCAB) theoretically. This indicates a brand new way to measure the blood components concentration and a potential to provide absolute quantitation of hemodynamic variables. One of the systematic errors in the calculation of the component changes from NIRS data of the dynamic spectrum is the absolute magnitudes and relative differences in pathlength factors as a function of wavelength. Monte Carlo simulations are used in this paper to examine the importance and mitigation methods of this error while the photoelectric pulse wave is detected on the finger tip. We found wavelength selection to be important variables in minimizing such errors, and replacing the average pathlength factor with the subsection pathlength factor appropriately could reduce the error to a small fraction (10%).