聚焦超声换能器焦距与直径比值对高强度聚焦超声透过条状障碍物的生物学焦域的影响

The effects of the f-number of the transducer through the ribs on biological focal region in high intensity focused ultrasound ablation

目的探讨聚焦超声换能器的物理参数换能器焦距与直径的比值(f-number)对高强度聚焦超声(HIFU)透过条状障碍物的生物学焦域的影响。方法分别选用f-number为0.65(1.0-200-130)和f-number为0.85(1.0-200-170)型换能器在离体牛肝中进行HIFU辐照。将肋骨置于换能器与焦平面之间,HIFU声束轴线在B超的引导下,分别沿肋间隙正中聚焦、肋骨边缘聚焦和正对肋骨聚焦。在每种聚焦方式下,肋骨置于距焦平面3、6、9 cm处。HIFU声束透过肋骨聚焦,在牛肝中的辐照深度为20 mm,辐照功率250 W,辐照时间10 s;辐照方式采用定点辐照。辐照结束后切开牛肝,观察和记录生物学焦域的形成率与体积。结果在其他辐照参数相同的情况下,f-number为0.65透过肋骨后生物学焦域的形成率和体积均较f-number为0.85时大(除f-number为0.85正对肋骨聚焦,肋骨距焦平面3 cm外)。结论聚焦超声换能器f-number不同,HIFU透过肋骨所形成的生物学焦域形成率与体积不同。

Objective To investigate the effects of the f-number of the transducer through the ribs on biological focal region （BFR） in HIFU ablation. Methods f-number was 0.65 （ 1.0 - 200 - 130 ） and f-number was 0.85 （ 1.0 - 200 - 170 ） type transducer were selected for the experiment of BFR. Bovine Liver in vitro was prepared for experiment. The ribs were placed between the focal plane and transducer, the beam axis was directed to the intercostals space, the rib edge and the centre of middle rib under ultrasound guidance. For each of the method, the plane of the front surface of ribs was placed 3, 6 and 9cm in front of the focus plane. The depth of exposure in liver was 20 mm, exposure power was 250 W, exposure time was 10 s, exposure mode was dot. Liver was cutdown after HIFU exposure, the TNR and volume of the BFR were measured. Results The different f-number of the transducer had different effects on BFR in HIFU ablation through the ribs. The TNR and volume of BFR were larger in f-number was 0.65 than those in f-number was 0.85, except f - number was 0.85 which directed to the centre of middle rib, and the focus plane exceeds 3 cm. Conclusion When the f-number of the transducer is different, the TNR and the volume of BFR through the ribs are different.