聚丙烯酰胺(PAA)模块高强度聚焦超声消融实验研究:消融灶的可视化及其显像特点

Ablation experiments of high intensity focused ultrasound in polyacrylamide phantom for optical visualization of ablation lesion and its imaging

目的了解聚丙烯酰胺(PAA)凝胶模块在高强度聚焦超声(HIFU)消融灶形成过程中的可视特性,观察模块内HIFU消融灶的超声及磁共振显像特点。方法采用HIFU辐照30％蛋清的PAA凝胶模块后,用肉眼观察消融灶的形成过程、消融灶的颜色、大小和形态变化。超声和磁共振显像观察消融灶的回声或信号改变。结果HIFU辐照声功率为240w、辐照时间≥0．1 s时,PAA模块内形成的焦区消融灶呈乳白色不透明区,随辐照时间延长,消融灶扩大主要向浅部延伸,其形态从米粒样向倒置锥形或三角形演变;同一辐照深度,消融灶的长度、宽度随辐照时间的增加逐渐增大;辐照深度不同时,HIFU形成的消融灶长度、宽度随治疗深度的增加而逐渐减小。模块内消融灶在超声图像上表现为高回声区,在磁共振成像上,T1加权相信号变化不明显,T2加权相呈低信号。结论PAA凝胶模块具有能用肉眼观察HIFU辐照后消融灶形成过程的可视化特性,其内消融灶可被影像学显示,这将对生物体的HIFU声场、温度场和消融灶及其相互关系的深入研究具有重要意义。

Objective To investigate the visualization characteristics of formation of ablation lesion induced by high intensity focused ultrasound （HIFU） in polyacrylamide （PAA） phantom as a model and its imaging. Methods The formation of ablation lesions was observed visually during and after radiation of HIFU（acoustic power 240w, radiation time ≥0.1s）. Ablation lesions within PAA phantom were detected by both ultrasonography and magnetic resonance imaging （MRI）. Results After radiation of HIFU, the focal ablation lesions induced by HIFU within the phantom appeard white. The focal ablation lesions during radiation of HIFU expanded mainly to near part of focus with radiation time increased. The change of ablation lesions turned from rice-like to inversed triangular shape. The length, width and volume of ablation lesion increased with radiation time increasing under the same condition of acoustic intensity and radiation depth , but those decreased with radiation depth increasing under the same condition of acoustic intensity and radiation time. The echogenicity of ablations was hyperechoic. The signal changes of the ablation were not apparent with T1-weight, while that of T2-weight was low signal. Conclusions There was a visualization characteristic of ablation lesions formation in PAA gel phantom after HIFU radiation. The ablation lesions can be detected by imaging modalities. It is important for the research of HIFU acoustic field, temperature field, ablation lesions formation and the relationship among them.