Nonlinear Parameter Tomography by Secondary Sound Waves

Abstract

Acoustic nonlinear parameter can be defined by the ratio of coefficients of quadratic term to linear term in the Taylor expansion of pressure-density relationship for a medium, and is a very basic parameter in nonlinear acoustics. In recent ten years much attention has been focused on the investigation of acoustic nonlinear parameter in biological media due to the occurrence of nonlinear phenomena, such as wave distortion,harmonic generation,acoustic saturation etc., in the range of biomedical frequencies and intensities. The existence of these nonlinear ultrasonic effects can accelerate the sound losses and limit the amount of sound power deliverable to the media. Thus, the wide applications of ultrasound in medical diagnosis and therapy have increased the importance and necessity to study the nonlinear properties, especially the nonlinearity parameter B/A in biological media. Moreover, many works indicate that the nonlinear parameter B/A is evidently dependent on the structural hierarchy of specimens and is sensitive to the pathological state of tissues. Therefore, this parameter consists of dynamical information of the materials and is expected to become a new parameter in tissue characterization and imaging.