To improve the cavitation-to-tissue ratio (CTR) of cavitation imaging during the treatment with high-intensity focused ultrasound (HIFU), we proposed a pulse inversion based broadband subharmonic cavitation imaging method (PIBSHI). Due to the fact that the subharmonic signal is a unique nonlinear vibration characteristic of cavitation bubbles, we extracted the broadband subharmonic signal to get a high-CTR cavitation imaging. The simulation showed that the subharmonic signal produced by cavitating bubbles with different sizes varied, and the signal was stronger than other subharmonics when the bubbles' resonant frequency was close to 1/2 subharmonic frequency. Further experiment results demonstrated that compared with the conventional B-mode images, broadband subharmonic cavitation imaging (BSHI) has improved the CTR by 5.7 dB, and the CTR was further improved by 3.4 dB when combined with pulse inversion (PI) technology. Moreover, when the bandwidth was set to 100%~140% of the 1/2 subharmonic frequency in PIBSHI, the CTR was the highest and the imaging showed the optimal quality. The study may have reference value for the development of precise cavitation imaging during HIFU treatment, and contribute to improve the safety of HIFU treatment.
为了提高高强度聚焦超声（HIFU）治疗过程中空化成像的空化组织比（CTR），本文提出一种基于脉冲逆转的宽带次谐波主动空化成像（PIBSHI）方法。次谐波是空化泡群在声场中进行非线性振动时所产生的独有的信号，而提取宽带次谐波信号进行成像能够有效改善图像的 CTR 值。本文通过仿真结果表明，不同尺寸空化泡群所产生的次谐波信号不同，其中谐振频率接近 1/2 次谐波频率的空化泡群所产生的次谐波信号强度最大。进一步的实验结果表明，相较传统的 B 模式（B-mode）空化成像，宽带次谐波空化成像 (BSHI) 的 CTR 值可最多提高 5.7 dB，结合脉冲逆转技术后，图像的 CTR 值进一步提高 3.4 dB。此外，在 PIBSHI 成像中，带宽范围设置为 1/2 次谐波频率的 100% ～ 140% 时，图像的综合质量最佳。本文结果为发展 HIFU 治疗过程中的精准空化监控成像提供新的思路，有助于提高 HIFU 治疗的安全性。.
Keywords: broadband subharmonic cavitation imaging; cavitation-to-tissue ratio; high-intensity focused ultrasound; pulse inversion technology.