Ultrasound Contrast Imaging Based on a Novel Algorithm Combined Pulse Inversion with Wavelet Transform

In this article, an ultrasound contrast imaging method that combines the pulse-inversion technique with wavelet transform has been proposed to enhance the contrast between bubbles and surrounding tissues. In this technique, wavelet transform is utilized to analyze the correlation between mother wavelet and the received echoes from a pair of inverted transmit pulses, respectively. To obtain a better correlation, a new mother wavelet named “bubble wavelet” is constructed according to the modified Herring equation. Radio-frequency (RF) data were acquired from a modified digital diagnostic ultrasound system that transmits two identical pulses with opposite polarity. The proposed method was validated by simulations. Experiments were performed on an ultrasound flow phantom and results showed that the contrast-to-tissue ratio (CTR) was improved by up to 28 dB depending on types of mother wavelet, scales and depths, compared with that obtained using pulse-inversion-based second-harmonic imaging. Experiments in vivo were also conducted out using kidneys of rabbits and results showed that the signals of surrounding tissues can be well suppressed compared with that of bubbles. The proposed method was compared with the quadratic pulse inversion (QPI) imaging on the same set of experimental data. Further improvements might be achieved with optimized bubble wavelet and imaging algorithm.