A frequency compounding technique for improving the point spread function of superharmonic imaging systems.

Abstract

Compared to fundamental imaging, harmonic imaging improves the axial and lateral resolution, while reducing the reflections from nearby artifacts and suppressing the effect of grating lobes. Superharmonic imaging combines reflections from the third, fourth, and fifth harmonic of the transmitted ultrasound pulse to improve the image quality of medical echography. A drawback of adding harmonic reflections is the possible degradation of the point spread function by ripple artifacts. The dual pulse technique reduces these ripples by transmitting two consecutive pulses with a slightly shifted frequency, and imaging the sum of both superharmonic reflections. Because two pulse-echo cycles are required, the frame rate is half that of a single pulse technique. In this presentation, a frequency compounding technique is described for a superharmonic imaging system with an interleaved phased array. With this technique, both frequency-shifted pulses are transmitted simultaneously by the odd and even transmit elements, respectively. Numerical results obtained with the iterative nonlinear contrast Source method are shown. Moreover, these are validated against experimental results. The results show that frequency compounding provides the benefits of the dual pulse technique while avoiding reduction of the frame rate. [Work supported by STW and NCF.]