基于声辐射力脉冲的HIFU焦点监控

HIFU Focus Monitoring Based on Acoustic Radiation Force Pulse

目的通过仿体实验,验证声辐射力脉冲成像方法在术前探测高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)焦点位置的可行性。方法利用HIFU换能器产生时间长度分别为200、600、900 ms的声波激励信号,这些声波在仿体内部可产生声辐射力脉冲并推动焦域的仿体组织发生位移。使用超声影像技术中的运动成像方法(Loupas二维互相关算法)对该位移信息进行监测。由于焦域处能量大,声辐射力在焦域内产生的位移大于焦域外的区域,根据组织运动幅值的空间二维分布来确定焦域位置。结果声辐射力脉冲在仿体组织中产生的位移可被超声影像技术监测到,组织运动幅值的空间二维分布图能够准确反映HIFU治疗的焦域位置信息。由该方法得到的焦点位置与换能器的几何焦点相差5 mm,更接近实际焦点。结果显示,激励脉冲的长短对组织运动监测的影响较大,当激励时间长度为200 ms时,所获得的组织位移分布最符合焦域的实际能量分布情况,增长激励时间,受热扩散和组织凝固影响,所得位移分布呈扩散趋势。结论通过监测HIFU换能器的声辐射力所产生的组织运动,在仿体上验证了术前对焦点进行定位的可行性,利用该技术可提高HIFU手术的安全性。

Objective Through the in-vitro experiment,the feasibility of acoustic radiation force impulse imaging in detecting the focal position of high intensity focused ultrasound(HIFU)before operation was validated.Methods The HIFU transducer was used to generate acoustic excitation signals with time lengths of 200,600 and 900 ms respectively.These sound waves generated acoustic radiation force pulses inside the mimics and push the mimics tissue in the focal domain to shift.The motion imaging method(Loupas two-dimensional cross-correlation algorithm)in ultrasonic imaging technology was used to monitor the displacement information.Due to the large energy in the focal region,the displacement of the acoustic radiation force in the focal region was larger than that outside the focal region.The focal region position was determined according to the two-dimensional spatial distribution of the tissue motion amplitude.Results The displacement of acoustic radiation force pulse in the mimicked tissue could be monitored by the ultrasound imaging technique,and the two-dimensional distribution map of tissue motion amplitude could accurately reflect the focal position information of HIFU radiation.The focus position obtained by this method was 5 mm different from the geometric focus of the transducer,which was closer to the actual focus.The results showed that the length of the excitation pulse had obvious influence on the motion estimations.When the excitation time length was 200 ms,the tissue displacement distribution obtained was most consistent with the actual energy distribution in the focal region.With the increase of the excitation time,the displacement distribution showed a diffusion trend due to the influence of heat diffusion and tissue solidification.Conclusion By monitoring the tissue movement caused by the acoustic radiation force of the HIFU radiation,the feasibility of preoperatively locating the focal point is verified on the mimics,and the safety of HIFU surgery can be improved by using this technique.