ACOUSTO-OPTIC IMAGING TECHNIQUES FOR OPTICAL DIAGNOSIS

The combination of light and ultrasound to measure optical properties through thick and highly scattering media is a tantalizing approach for \emph[in vivo] imaging. This is partly due to the ballistic nature of ultrasound in biological tissue and thus the well-defined localization of the signal with a mm3 resolution. Optics can reveal echography-silent tumors by monitoring the wavelength of the laser source and thus measuring the optical absorption linked to oxy- or deoxyhemoglobin. The coherent nature linked to the acousto-optic effect allows interferometric measurements. A difficulty arises from the speckle nature of the light to analyze, and two techniques with a high etendue are available at present in order to eliminate speckle blurring. They use either a CCD-camera that treats independently each grain of speckle, or a large area single detector and a photorefractive crystal that adapts the wavefront of the reference beam to the speckle output pattern.