中文摘要：

目的探讨工作周期（即占空比）在脉冲高强度聚焦超声（HIFU）损伤组织的生物学效应中的作用。方法设置HIFU辐照参数使能量恒定,按不同工作周期与相应辐照时间分组,观察各辐照焦点温度、灰度以及组织学改变。结果HIFU辐照离体牛肝时,25%组、50%组、75%组和100%组最高温度大于85℃且有明显的凝固性坏死。1%组、5%组、15%组最高温度不高于56℃且无肉眼可见的坏死改变。15%组光镜下见细胞间裂隙增宽,肝细胞胞浆内见大小不等空泡。结论长工作周期易形成热凝固性坏死,而短工作周期则可能通过空化机械效应损伤组织。

英文摘要：

Objective To investigate the affect of duty cycle on in vitro bovine liver treated with pulsed high intensity focused ultrasound. Methods Total energy was held constantly for each parameter set. Grouping was based on different duty cycles and corresponding exposure time. The changes of temperature .gray scale and histology were observed. Results In maximal temperature of group 25 %. 50%, 75% and 100%（〉 85 C ）, tissue necrosis was visualized obviously. In maximal temperature of group 1%. 5% and 15%（≤ 56 C）, no necrotic changes were observed with naked eye. The cellular interstitial space was widened and aniso-size vacuoles in hepatic cyotoplasm were present under optic microscopy in group 15 %. Conclusions Long duty cycle may form tissue necrosis because of heat effect ,but short duty cycle may damage tissues and cells by cavitation with mechanical effect.