Optical tomography in scattering media from photon time-of-flight diffuse reflectance measurements: a chemometric approach

Abstract

The goal of this project is to develop practical methods for quantitative, depth-resolved optical imaging in scattering media. Toward this end, reconstruction techniques based on photon time-of-flight and autocorrelation measurements of diffuse reflectance are being studied. The approach employs an array of radial intensity measurements to obtain information sensitive to subsurface changes in absorption. Both Monte Carlo simulations and experimentally obtained measurements of known phantoms were used in the evaluation of reconstruction techniques. Time-gated single-photon reflectance measurements were made using a pulsed laser illuminating a layered absorbing/scattering sample. For image reconstruction, stagewise multilinear regression, inverse and partial least squares methodologies were investigated. With all methods, absorbance was better estimated in the top regions as compared with deeper regions. Both PLS and SMLR methods gave significantly better estimation of sample absorption as compared with the ILS technique. Reconstruction results using autocorrelated data were found to provide a similar estimation of absorption in comparison with time domain data. The use of autocorrelation measurements could significantly reduce the complexity of instrumentation for obtaining time-resolved information to study spatial relationships of absorbing constituents in scattering media. Copyright­© 1999 John Wiley & Sons, Ltd.