Ultrasound-modulated optical tomography using four-wave mixing in photorefractive polymers

Abstract

ABSTRACT Ultrasound-modulated optical tomography uses a well focused ultrasound beam to modulate diffuse light inside soft biological tissues. This modality combines the advantages of ultrasound resolution with optical contrast. However, because of the low ultr asound modulation efficiency, the large background of un-modulated phot ons gives a low signal-to-noise ratio. Here we report a technique for detection of ultrasound-modulated light using a phase conjugated signal generated by four-wave mixing in a photorefractive polymer. The experimental results demonstrate the potential of this method to detect ultrasound-modulated optical signals in a highly scattering media with an excellent signal-to-noise ratio. Keywords: Ultrasound-modulated optical tomography, four wave mixing, photorefractive polymer, phase conjugate 1. INTRODUCTION Optical imaging of soft biological tissue has become an increasingly interesting topic in biomedical research. Though pure optical imaging provides excellent optical contrast, it lacks good spatial resolution especially for the strong scattering present in a thick biological sample. Various imaging modalities have been proposed to overcome this difficulty, among which the ultrasound-modulated optical tomography (UOT)