Real-Time Nonlinear Parameter Tomography Using Impulsive Pumping Waves

Absrruci-In this paper a novel real-time tomographic system for imaging the nonlinear parameter B/A of biological objects is proposed. This parameter is related closely to the detailed structure and property of tissues, and may well provide a new dimensional and powerful tool for ultrasonic tissue characterization. In this system an impulsive, relatively high-power pumping wave is applied from a direction perpendiculax to the continuous low-intensity high-frequency probing wave so that the phase of the probing wave is modulated instantly by the product of the parameter B/A of the object and pressure of the pumping wave. Then the resulting spatially-modulated probing wave is detected and demodulated to derive the distribution of B/A along the probing beam. An inverse-filtering operation is employed to compensate for the spread of the pumping wave. The processes are repeated by shifting the position of the probing beam and a two-dimensional image is obtained. A prototype of the imaging system is constructed and images related to the nonlinear parameter of phantoms and human tissues are obtained. The usefulness of this method is shown in these experimental results.