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An Enhanced Chirp Modulated Golay Code for Ultrasound Diverging Wave Compounding

In ultrasound imaging, a straightforward way of increasing axial resolution is by shortening the transmitted signals. However, short excitation provide low echo signal to noise ratio (eSN R), which results in low image quality. An alternate solution would be to increase the excitation signal's duration (by using binary Golay codes or chirps), and rely on off-line match filtering techniques in order to compress the received echoes. Resolution Enhancement Compression (REC) is a coding technique that provides better axial resolution than conventional pulsing technique while increasing the eSNR. It consists on designing a pre-enhanced chirp that compensates the most attenuated frequency bands of the ultrasound probe. The objective of this study is to combine orthogonal binary codes with REC pre-enhanced chirps in order to boost further the eSNR provided by REC while keeping its good performance in axial resolution. The method is applied to diverging wave compounding. Pairs of diverging waves are transmitted/received/reconstructed simultaneously thanks to the orthogonality property of the Golay codes. The results show that the proposed method is able to obtain a better image quality than conventional pulse imaging. The axial resolution and the bandwidth was improved by 38%/15% in simulation/experiment, for an excitation signal designed to provide a 39% boost. The contrast to noise ratio and the eSNR were improved by 3.5dB and 18.7dB respectively. Acquisition results suggest that the combination between binary codes and modulated enhanced chirps can be implemented in ultrasonic imaging system.