Evaluation of the temporally extrapolated absorbance method for dual-wavelength imaging through tissuelike scattering media

An independent assessment is described of a dual-wavelength imaging technique, known as the temporally extrapolated absorbance method (TEAM), proposed by Yamada et al. [Opt. Eng. 52, 634-641 (1993)]. The technique involves recording the temporal distribution of light transmitted across a scattering medium at two carefully chosen wavelengths at which the scattering properties of the medium are assumed to be identical. The objective is to image internal structure that absorbs more strongly at one wavelength than it does at the other. A simple theoretical treatment of TEAM is presented that employs a perturbation model of photon transport. This indicates that despite the lack of a secure theoretical basis, the technique may provide a potentially effective ad hoc method of generating images of highly scattering media. The method was also evaluated experimentally by using, for the first time to our knowledge, a single object and two wavelengths. A single-projection, two-dimensional image was obtained of a solid phantom with optical properties representative of breast tissue. The results exhibited good agreement with the theoretical model, and a small embedded feature that absorbs 3.5 times as strongly as the surrounding medium at one wavelength was revealed successfully. (C) 1997 Optical Society of America.