Simultaneous imaging of absorption and scattering in dc diffuse optical tomography

We present new results on the fundamental nonuniqueness issue in dc diffuse optical tomography (DOT) that resolve a long-standing conflict between theory and practice. Theoretically, scattering and absorption properties of the imaged media were proven to produce equivalent and thus indistinguishable effects. However, successful simultaneous reconstructions of both parameters were obtained in phantom experiments. We reconcile theory and practice by showing that the equivalence of scattering and absorption is only true for spatially smoothly varying scattering properties. Jumps in the scattering properties are however distinguishable from absorption effects. In fact, in composite tissue consisting of regions with constant scattering properties, dc intensity measurements in DOT are sufficient to simultaneously image both the absorption and the scattering coefficient. We give an intuitive justification for this result and conjecture a complete theoretical characterization of what can be reconstructed from dc intensity measurements in DOT. Essentially, the reconstructable quantities consist of the effective absorption properties together with the jumps of the scattering coefficient and its first derivative.