Experimental implementation of the second harmonic inversion imaging on an open ultrasonic scanner

Ultrasound harmonic imaging is limited by the harmonic components which are produced during wave propagation because of the native nonlinearities of the tissue. A newly proposed method, named Second Harmonic Inversion (SHI) suggests transmitting successively two pulses with the same frequency, the same amplitude and a 90° phase difference to reduce the second harmonic generated by tissue. This newly proposed SHI method is carried out on an open system equipped with a bipolar square-wave pulser and a linear probe. Measurements performed in water, on a general purpose ultrasound phantom and with a tissue mimicking phantom with circulating contrast agents are investigated. Experimental results show that SHI method can be easily implemented on an open system. Both radio frequency signals analysis and B-mode ultrasound images show that SHI method decreases significantly the native second-harmonic tissue components existing in standard harmonic images. Contrast-to-tissue ratio (CTR) of SHI image is improved by 4.6dB when compared to standard harmonic image and improved by 3.6dB when compared to PI image. SHI method enhances CTR through effective tissue generated second harmonic reduction. Moreover, the easy implementation procedure and the better specificity make SHI an interesting alternative to PI method.