In situ local tissue characterization and imaging by backscattering acousto-optic imaging

We use an imaging system taking advantage of a focused ultrasonic field to mark the photon trajectories in a biological sample by modulating the optical paths in the focal zone. We show the applicability of this setup to various geometrical configurations, such as forward and backward scattering. The modulated speckle detected on a CCD camera reflects, after parallel processing, the local optical properties of the tissue in the focal zone. We propose to use the backscattering geometry to estimate the local effective attenuation coefficient. Finally we compare images which have been obtained through several centimeters of biological tissue, both in forward and in backward geometry.