Diffuse photon density wavefront speed as a contrast for tomographic imaging of heterogeneous diffusive media.

An imaging algorithm is implemented for tomographically reconstructing contrast maps of the space variant speed of diffuse photon density wavefronts (DPDWFs) propagating in biological tissue-like diffusing media. This speed serves as a novel contrast not previously exploited in the literature. The algorithm employs early photon arrival times (EPATs) extracted from a set of time domain measurements. A relationship between EPATs and the speed of DPDWFs is exploited as the forward model. The forward model and its use in an inverse problem are supported by experimental results. These are carried out for 3D media with tissue-like optical properties. The resulting inverse problem is formulated as a set of algebraic equations and solved within a constrained linear least squares framework. The results indicate that the algorithm provides tomographic information on heterogeneities locations and distributions.