A Monte Carlo modeling technique was used to simulate ultrasound-modulated optical tomography in inhomogeneous scattering media. The contributions from two different modulation mechanisms were included in the simulation. Results indicate that ultrasound-modulated optical signals are much more sensitive to small embedded objects than unmodulated intensity signals. The differences between embedded absorption and scattering objects in the ultrasound-modulated optical signals were compared. The effects of neighboring inhomogeneity and background optical properties on the ultrasound-modulated optical signals were also studied. We analyzed the signal-to-noise ratio in the experiment and found that the major noise source is the speckle noise caused by small particle movement within the biological tissue sample. We studied this effect by incorporating a Brownian motion factor in the simulation.
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