Research On Coded Excitation Characteristics Of Ultrasound Imaging

Ultrasonic intensity transmitted in biological tissue must be within the safe threshold, because of the limitation of ultrasonic thermal and cavitation effect, so the excitation amplitude of single pulse used in traditional medical ultrasonic imaging system is limited. And the signal to noise ratio (SNR) of detecting the deep tissue is unsatisfactory due to the large attenuation of high-frequency ultrasound with high-resolution. The technology of coded excitation and pulse compression can separately improve the average sound power of transmission signal and the resolution of echo signal, which can better solve this problem. The pulse compression performance of signal was researched in this paper based on the coded excitation methods of linear frequency modulation (LFM), Barker and Golay code. The relevance between the peak-side-lobe level (PSL) after pulse compression and the bandwidth?scanning time of LFM signal was also studied. Then a new coded excitation signal, which utilizes the chirp signal with amplitude modulated (abbreviated as AM-chirp) as the carrier to modulate Golay code, is proposed in this paper. It was abbreviated as AM-chirp-Golay. The optimal pulse compression performance was obtained by changing the amplitude of AM-chirp-Golay signal, bandwidth of AM-chirp carrier (B) and duration of Golay code (T).Theoretical and experimental studies have showed that:(1) The peak-side-lobe level of signal with pulse compression decreases with the increase of the bandwidth and scanning time of LFM signal, after it excites the transducer. The tapering/filtering scheme of Kaiser window function better solve the tradeoff problem between the pulse compression resolution and the PSL, which obtained the better imaging effect.(2) The proposed amplitude modulation scheme of AM-chirp-Golay signal achieved the favorable side lobe suppression effect. The Kaiser amplitude modulation scheme can reduce PSL to below -75dB on the basis of less resolution loss, solving the problem between axial resolution and SNR, PSL.The research results in this paper can provide ideal technical solutions for improving the performance of deep tissue's high-resolution ultrasonic imaging.