The key problems of optical transmission imaging of thick complex biological objects are strong diffusion (scattering) and non-uniform intensity distribution of transmitted signal across the scanned area. These constraints essentially reduce the spatial resolution and uniformity of the overall pattern. We report on implementation of a new approach of signal detection scheme, which relies on synchronization of lock-in amplifier with a temporal step of laser beam discrete scanning. This technique is favorable for preferential detection of abrupt spatial features, increase of contrast and substantial reduction of overall non-uniformity of image brightness. On the other hand, the lock-in detection scheme, being phase-sensitive, helps to some extent to enhance the contribution of least-deflected photons in the recorded signal thus suppressing the diffusion component. We present the results of measurements showing efficiency of the proposed scheme.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.