Multiresolution analysis for quantification of optical properties in scattering media using pulsed photon time-of-flight measurements

A simplified photon time-of-flight (TOF) instrument based on a nanosecond rise-time diode laser at 635 nm was used for the quantification of optical properties of samples. A series of transmittance photon time-of-flight measurements were acquired from absorbing/scattering Intralipid™ samples of known composition (0<μ_a<0.0014 mm⁻¹; 13<μ_s<24 mm⁻¹). Time-of-flight distributions were analyzed using Haar transform with selection of the most parsimonious set of wavelets by genetic algorithm optimization. Results showed that the scattering coefficient could be estimated with a coefficient of variation (CV) of 4.4% and r²=0.95 using wavelets of frequency up to 400 MHz. Absorption coefficients were estimated with a CV of 6.9% and r²=0.99 using steady-state intensity of blank- and scatter-corrected data. Furthermore, it was shown that quantification using simplified electronics can estimate scattering to within 7.2% (r²=0.88) and absorption with an error of 8.3% (r²=0.99). The above findings suggest that a simplified instrument based on a pulsed laser diode and low frequency switches could be developed to quantify absorption in highly scattering media.