Imaging in turbid media by photon density waves: spatial resolution and scaling relations.

Spatial resolution of transillumination imaging through highly scattering media normalized to sample thickness d depends on only the normalized wavelength ?/d of photon density waves and normalized penetration depth delta/d. This was concluded theoretically and verified experimentally by the derivation of edge-spread functions from measured time-resolved transmittance and its Fourier transform by the use of dilute milk at various concentrations as scatterer in cuvettes of d = 2 cm and d = 4 cm. In the frequency domain and the time domain, spatial resolution was found experimentally to be given by approximately 0.3 d obtained at ? approximately d or when only the first arriving 1% of all photons detected were taken into account.