A perturbation approach for optical diffusion tomography using continuous-wave and time-resolved data

In this paper, we discuss approaches our group has developed for the problem of imaging the interior of dense scattering media [1]. While our principal focus is on potential biomedical applications, we believe our methods are sufficiently general to have applications to other imaging problems as well. We begin our consideration of the imaging problem by assuming that the target medium of interest interacts with the penetrating energy source with sufficient strength to cause intense scattering. We further assume that for essentially all practical schemes, only the multiply scat- tered signal is measurable. One result of multiple scattering is that all the detected photons will have propagated above and below the plane in which the source and de- tector lie. Thus, it becomes necessary to explicitly consider volume functions whose spatial distribution will depend on the properties and geometry of the medium and on the geometry and type of illumination scheme. Measurement schemes which have been suggested include steady-state [2], ultrafast [3-5], and amplitude mod- ulated [6, 7] sources. Other schemes include holographic methods which have the potential advantages of directly yielding an image without the need for numerical reconstruction [8, 9]. In developing approaches to image reconstruction, our group has emphasized the first two of the four methods [10-16].