Laser speckle statistics in ultrasound-modulated optical tomography

Ultrasound-Modulated Optical Tomography is a novel biophotonic imaging technique that provides optical contrast with ultrasonic spatial resolution. High temporal coherence laser light and focused ultrasound are transmitted into tissue. Light passing through the acoustic focal volume experiences modulation due to acoustically induced changes in optical index of refraction and optical scatterer displacement. A component of the modulated light may be detected using various detection schemes. One such scheme detects changes in the contrast of optical speckles using a CCD camera. We use statistical optics to derive expressions for the speckle statistics as a function of acoustic parameters. We demonstrate theoretically and experimentally that low acoustic frequencies induce much larger modulation compared with high frequency ultrasound. Theoretically computed values for the speckle contrast are compared with experimental values