Medical Ultrasound Imaging Using Pulse Compression Technique Based on Split and Merge Strategy

A medical ultrasound image with a high spatial resolution and a high signal-to-noise ratio (SNR) is required for precise diagnosis. However, when a long chirp pulse is transmitted in order to improve the SNR, both the transmitted signal and the echo signal overlap. The dynamic range of the analog-to-digital (A/D) converter should be adjusted to that of the echo signal, and the transmitted pulse is saturated. Therefore, the transmitted pulse cannot be compressed completely, and the echo signal cannot be extracted from the overlapped signal. This indicates that a long chirp signal makes near-field imaging impossible. In this paper, we propose a method that can realize near- and far-field imaging processes with higher SNRs. The proposed method is based on a split-and-merge strategy. As a result, it is shown that our proposed method gives both near- and far-field images with approximately 40 dB higher SNRs than the short pulse.