Enhanced Second Harmonic Imaging Using a Pulse Compression Technique Combined with Ultrasound Pulse Inversion

Pulse Inversion (PI) is a transmission technique used for harmonic imaging. By transmitting two phase inverted signals, which allow cancelling out the fundamental component, PI is able to achieve better image quality thanks to the reduced clutter/reverberation and to the improved bandwidth of the second harmonic. Here, a technique based on Resolution Enhancement Compression (REC) that improves the performance of PI is proposed. It consists in boosting the energy of the excitation signal at the frequencies where the probe is less efficient, which further improves the bandwidth of the second harmonic signal. The proposed approach (REC-PI) is combined with coherent plane wave compounding and implemented on the UlaOp-256 ultrasound scanner. Promising results are obtained from in-vitro experiments using an excitation signal designed to provide a 35% increase in axial resolution over the one obtained with a broadband pulse excitation. The experimental measured axial resolution from the echoes was improved by 25.4% for the wire phantom, when using the REC-PI technique compared to classical PI. Further, the axial speckle size evaluated on the in-vitro phantom B-mode image was enhanced by 20%. The CNR was also improved by 18.2 dB. These results demonstrate the feasibility of our approach and its implementation on the research scanner UlaOp-256.