Ultrasound contrast imaging based on a novel algorithm combined pulse inversion with wavelet transform

In this paper, a novel ultrasound contrast imaging method which combines the pulse-inversion technique with wavelet transform is proposed in order to enhance the contrast between bubbles and surrounding tissues. Wavelet transform is utilized to analyze the correlation between mother wavelet and received echoes from a pair of inverted transmit pulses respectively. In order to obtain better correlation, a new mother wavelet named ldquoBubble waveletrdquo is constructed according to the modified Herring equation. Radio frequency (RF) data were acquired from a modified digital diagnostic ultrasound system. Experiments were performed on an ultrasonic flow phantom and results showed that the contrast-to-tissue ratio (CTR) was improved by 6.4-16.0 dB depending on types of mother wavelet, scales and depths, compared to that obtained using pulse-inversion-based second-harmonic imaging. Experiments in vivo were also conducted out using kidneys of rabbits and results showed that signals of surrounding tissues can be well suppressed compared to that of bubbles. By using Bubble wavelet, the CTR is improved by up to 9.6 dB relative to Morlet wavelet and Mexican Hat wavelet under the same conditions in experiments. Further improvements might be achieved with optimized bubble wavelet which can describe the scattering echoes of the bubbles more accurately.