HIFU在牛肝组织中的传播衰减研究

运用辐射压力法研究高强度聚焦超声在牛肝组织中的传播衰减。在室温 2 0℃下 ,利用 4种治疗超声换能器 ,在不同的换能器表面输出声功率下 ,分别测量 2 0、4 0、6 0、80 m m不同厚度新鲜离体牛肝在放入脱气水前后的声辐射力 F、F′,然后计算出声衰减。使用治疗超声换能器 4 ,对于不同辐照深度 ,以声强 ISATA=2 2 .0× 10 3W/cm2、辐照时间 5 s的超声剂量定点辐照新鲜离体牛肝 ,以断层方式剖开后测量凝固性坏死组织体积。研究结果表明 ,对于一个具体的治疗超声换能器 ,在牛肝厚度一定时 ,辐射力穿透率 F′/F法与换能器表面声强及样品近治疗超声换能器表面声窗面积无关。采用最小 F′/F法拟合得出辐射力穿透率随牛肝厚度增加呈指数规律递减 ,且与凝固性坏死组织体积随牛肝厚度 (辐照深度 )增加呈指数规律递减趋势一致。采用最小二乘法拟合得出高度聚集超声在牛肝组织中传播的声衰随频率近似线性增加且呈幂函数关系。这为进一步研究高强度聚焦超声治疗剂量学提供了实验依据

Study of Ultrasound Attenuation During HIFU Propagation in Ox Liver

Ultrasound attenuation has been measured during HIFU propagation in fresh ox liver at different frequency using a radiation force method. The acoustic radiation force was measured before and after the prepared ox liver of various thicknesses (20 mm, 40 mm, 60 mm, 80 mm) which were put into degassed water and exposed to different transducer surface output acoustic powers at a room temperature (20 degrees C) with therapeutic transducers of various frequencies, and then the ultrasound attenuation coefficient was calculated. With the use of therapeutic transducer 4, the focus of the ultrasonic beam was set to be 20 mm, 40 mm or 60 mm deep into the tissue surface using B-mode ultrasound guidance. A single exposure was performed with focal intensity ISATA = 22.0 x 10(3) W/cm2(ISATA, in degassed water) and exposure time 5 sec. The sample was cut after treatment to measure the volume of coagulative necrosis. For a specific therapeutic transducer, the radiation force ratio in liver of constant thickness is independent of the transducer surface sound intensity and the area of the ultrasound window at the sample front face. The radiation force ratio and the volume of coagulative necrosis induced by HIFU are plotted as the functions of sample thickness (or exposed depth), in which it can be seen that these two parameters have the same exponential dependence on sample thickness. The ultrasound attenuation coefficient alpha in ox liver is shown to be frequency f dependent, it almost linearly increases with frequency t. This work shows that such a study is feasible, and offers experimental data that will be useful for future HIFU dosage studies.