L. Leonardi et Dh. Burns, QUANTITATIVE CONSTITUENT MEASUREMENTS IN SCATTERING MEDIA FROM STATISTICAL-ANALYSIS OF PHOTON TIME-OF-FLIGHT DISTRIBUTIONS, Analytica chimica acta, 348(1-3), 1997, pp. 543-551
The long term goal of this project is to develop practical methods for
quantitative measurements of constituents in scattering media. Pulsed
femtosecond illumination and time-gated detection provide information
about the photon pathlength. The photon time distribution is non-line
arly dependent on three major parameters: the absorption cross-section
, the scattering cross-section, and the phase function describing the
degree of forward scattered light at each scattering event. To direct
the construction of simplified instrumentation, we have investigated t
he use of analytic descriptors of the time distributions, such as deri
vatives and moments. Objective selection of the processing techniques
were made using Stepwise Multi-Linear Regression to independently esti
mate the absorption and scattering coefficients. The method was tested
with simulated time distributions. Results demonstrate that mean time
of the trailing edge of the time profile can provide a quantitative e
stimation of the absorption coefficient when scattering is held consta
nt. The second moment of the time profile provides the best estimator
of the scattering coefficient with absorption held constant. When scat
tering and absorption vary simultaneously multiple parameters are requ
ired for quantitative estimates. The absorption coefficient estimates
require the mean fall time, mean rise time, and the first moment of th
e distribution with variable scattering. The second moment, the mean r
ise time, the mean fall time, and the peak area provide the best estim
ates for the scattering coefficient with variable absorption. These re
sults suggest that practical instrumentation may be developed which wo
uld allow for robust quantification in highly scattering media.