Acousto-optic imaging using a powerful long pulse laser and digital holography.

Abstract

Acousto-optic tomography is a technique that couples ultrasounds and light in order to measure local optical properties through thick and highly scattering media, e.g. human breast tissues. Thanks to the acousto-optic effect, we can get the optical contrast information given by light and get the spatial localization from the ultrasound longitudinal waves. The use of a powerful long pulse laser (1 ms, 200 mJ) helps to improve the sensitivity of the technique by raising the optical peak power and collect more ultrasound tagged photons. Moreover, its tunable wavelength around 780 nm is appropriate for biological imaging since it is where light has its maximum penetrating depth in tissues. Detection of acousto-optic signals is done by off-axis heterodyne digital holography on a high speed CMOS camera. This enables us to make a tunable spatio-temporal filter with a high signal to noise ratio. Experimentally, this technique enables to image optical absorbers embedded within a thick scattering media (a few centimetres). It is also theoretically possible to use a conventional pulsed ultrasound scanner to generate acousto-optic signals that can at the same time record ultrasound images, which will be a step toward multimodal imaging for breast cancer detection.