High-SNR ultrasound-modulated optical tomography with intense acoustic bursts

We present a novel signal-enhancement method for ultrasound modulated optical tomography that can increase the amount of modulated light, compared to previous methods. By applying intense acoustic bursts, particle displacements of several microns are possible at a very local scale. A CCD camera captured the speckle pattern emerging from a laser-illuminated tissue phantom and differences in laser speckle contrast were measured between ultrasound on and off states. When CCD triggering was synchronized with burst initiation, ultrasound radiation force-induced displacements were detected with our technique, and resulting shear waves were shown to degrade image contrast and spatial resolution. Deleterious effects of shear waves were minimized by delaying CCD camera acquisition several ms until shear waves are adequately attenuated. Our system signal-to-noise ratio (SNR) is sufficiently high to perform UOT scanning without signal averaging. Because of substantially improved SNR compared to previous techniques, the use of intense acoustic burst is a new promising method for ultrasound modulated optical tomography