Accuracy limits in the determination of absolute optical properties using time-resolved NIR spectroscopy

摘要

Abstract: Time-resolved spectroscopy of tissue is considered to be a powerful tool in the NIR that can readily measure absorption and scattering properties of diffuse media. This can be done employing curve-shape fitting of the experimental measurements to the diffusion equation. Several exponential factors however can significantly affect the accuracy of the method and should be taken under consideration when quantitative measurements are desired. In this work we examine the influence of laser time drift and jitter, limited excitation of waveguide modes in multimode collection fibers and the finite width of the impulse response. The percent error in absorption coefficient calculation grows with an average rate of 5% error per 20 ps of time-uncertainty while the percent error in determining the reduced scattering coefficient increases with a rate of 10% per 20 ps of time uncertainty. Deconvolution is found necessary to compensate for photon dispersion higher than 50 ps. Furthermore the quantification accuracy is shown to be dependent on the medium optical properties in a non-linear fashion due to intrinsic time-characteristics of the diffusion process.!7