低功率HIFU辐照离体牛肝后强回声出现的原因

目的 研究低功率高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)辐照离体牛肝组织后即刻B超声像图中强回声出现的原因.方法 磁共振(Magnetic Resonance Imaging,MRI)引导的HIFU在50W声功率下分别辐照脱气后的离体牛肝组织10s,20 s,30 s…90 s(实际辐照时间),采用辐照10 s停1 s的方式.在辐照过程中,使用MRI的GRE_TMap序列采集HIFU焦域处的温度,并使用被动空化检测( Passive Cavitation Detection,PCD)系统采集来自焦域的声信号,在LabVIEW开发平台上编程对该信号进行快速傅里叶变换得到其频谱,以判断是否出现空化特征信号.辐照结束后,特离体牛肝组织切成1～2 mm厚的薄片,找到凝固性坏死的最大面,置于加热至37℃的TTC(2,3,5 -氯化三苯基四氮唑)染色剂中染色2min后取出照相.结果 HIFU以辐照10s停1s的方式辐照离体牛肝组织9次后B超声像图中出现强回声,焦域处的温度升高至89.46±2.48℃,PCD系统所采信号的频 谱中未见空化特征信号.切开并染色后的离体牛肝组织在第2次10s的辐照后就有凝固性坏死出现.结论 未达空化阈值的低功率HIFU照离体牛肝组织后即刻B超声像图中强回声出现的原因是焦域处产生的沸腾泡.

Reason of Appearance of Hyperecho in B-mode Ultrasound Image after Ex Vivo Bovine Liver Exposed to High Intensity Focused Ultrasound (HIFU) with Small Acoustic Power

Objective To investigate the reason of appearance of hyperecho in B-mode ultrasound image after ex vivo bovine liver exposed to High Intensity Focused Ultrasound （HIFU） with small acoustic power. Methods The degassed ex vivo bovine livers were exposed to magnetic resonance imaging （MRI） guided HIFU with the acoustic power of 50 W for 10 s,20 s,30 s,... ,90 s （real exposure time） respectively, and the HIFU work mode was 10 s-irradiate with 1 s-stop to obtain the B-mode images. During the exposures,the temperatures in the focal region of HIFU were acquired with GRE_TMap of MRI. Acoustic signal were detected using the passive cavitation detection （PCD） system and then transformed to frequency domain on LabVIEW. After exposures,the bovine livers were cut into 1 - 2 mm slices, among which the maximum coagulation necrosis areas were found and stained with TTC （triphenyhetrazolium chloride） for 2 min at temperature of 37 ℃. Results The in- creased echogenicity in B-mode ultrasound image was seen after 90 s-irradiation. The temperatures in the focal region of HIFU increased to 89.46 ± 2448℃. Neither sub-harmonic nor broadband noise was seen in the frequency spectrum of the signals detected by PCD system, dem- onstrated no cavitation bubbles in the focal region. The coagulation necrosis appeared from the second 10 s-irradiation. Conclusion When no cavitation bubbles, the reason of appearance of hyperecho in B-mode image is boiling bubbles due to temperature rise in the focal region of HIFU during bovine livers exposed to HIFU with small acoustic power.