高强度聚焦超声辐照离体组织中空化泡和沸腾泡对辐照后即刻B超声像图中强回声的贡献

目的研究高强度聚焦超声(high intensity focused ultrasound,HIFU)辐照离体牛肝组织中的空化泡和沸腾泡对辐照后即刻B超声像图中强回声的贡献。方法将牛肝组织简单随机分成2组,每组20块。一组使用200 W声功率的HIFU辐照2 s,以在HIFU焦域处只产生空化泡,另一组使用50 W声功率的HIFU辐照80 s,以在焦域处只产生沸腾泡。在辐照过程中,使用置于HIFU声焦点旁1 mm的热电偶对焦域处的温度进行测量,并通过计算机的RS 232串口进行记录。同时,使用被动空化检测(passive cavitation detection,PCD)系统测取牛肝组织内传播出的声信号,并在LabVIEW开发平台上编程以获得该信号的频谱,计算该频谱在3～7 MHz内滤除谐波后的均方根值(root mean square,RMS)。记录HIFU辐照后即刻的B超声像图,与辐照前同一位置的声像图进行比较。辐照结束后将牛肝切开,观察是否有损伤形成。结果 200 W声功率的HIFU辐照离体牛肝组织后即刻B超声像图中有19次未出现强回声,PCD系统所检测信号的频谱中出现明显的宽带噪声,辐照开始后RMS增大,焦点处的最高温度为(61.10±6.18)℃。50 W声功率的HIFU辐照离体牛肝组织后即刻B超声像图中有19次出现强回声,PCD系统所测信号频谱中未见宽带噪声,RMS未见增大,焦域处的最高温度为(93.34±3.37)℃。辐照后,所有牛肝组织中均出现了凝固性坏死。结论 HIFU辐照后即刻B超声像图中强回声出现的主要原因是辐照过程中产生的沸腾泡,非空化泡。

Contribution of cavitation and boiling bubbles to hyperecho in B-mode ultrasound images immediately after in vitro tissue exposed to high intensity focused ultrasound

Objective To study the contribution of cavitation and boiling bubbles to hyperecho in B-mode ultrasound images immediately after in vitro bovine liver tissue exposed to high intensity focused ultrasound(HIFU).Methods Forty bovine liver tissue blocks were divided into group A and group B,20 in each group.Group A was exposed to 200 W acoustic power HIFU for 2 s to induce cavitation bubbles in the focal region of HIFU and group B was exposed to 50 W acoustic power HIFU for 80 s to induce boiling bubbles in the focal region of HIFU.Temperatures in the focal region of HIFU were measured using a thermocouple placed in the liver 1 mm beyond to the HIFU and recorded through RS 232 serial port.Signals of acoustic emission from bovine liver tissue were detected with the passive cavitation detection(PCD) system,their frequency spectra were detected with a program written on LabVIEW,and their root mean square(RMS) was calculated after filtration of harmonics at 3-7 MHz.B-mode ultrasound images immediately after HIFU exposures were recorded and compared with those before HIFU exposures.Livers were cut into sections for gross observation for liver injury.Results No hyperecho was observed in B-mode images of in vitro bovine liver tissues 19 times after 200 W acoustic power HIFU exposure.PCD system showed significant broadband noise in the frequency spectra of signals and increased RMS.The peak temperatures in the focal region of HIFU were 61.10±6.18 ℃.The hyperecho was found in B-mode images of in vitro bovine liver tissues 19 times after 50 W acoustic power HIFU exposure.PCD system showed no broadband noise in the frequency spectra of signals and increased RMS.The peak temperatures in the focal region of HIFU were 93.34±3.37 ℃.Coagulation necrosis occurred in all bovine liver tissues after exposures.Conclusion The main reason why hyperecho is found in B-mode ultrasound images of in vitro tissues immediately after exposed to HIFU is the boiling bubbles rather than cavitation bubbles.