Ultrasound-modulated laser tomography

An ultrasonic beam was focused into a biological tissue sample to modulate the laser light passing through the ultrasonic beam inside the tissue. The speckle field formed by the transmitted laser light was detected by a CCD camera with the source-synchronous-illumination lock-in technique. The ultrasound-modulated laser light reflects the local optical and mechanical properties within the ultrasonic beam and can be used for tomographic imaging of the tissue. Spatial resolution along the ultrasonic axis was achieved by sweeping the ultrasonic frequency. Two-dimensional images of biological tissue were successfully obtained with both single frequency modulation and frequency-swept modulation. Three-dimensional images could be acquired as well in principle.