Effective characteristics of ultrasound for thrombolysis. -Appropriate frequency, waveform, mode of ultrasound emission, character of micro bubble-

研究了合适的频率、波型和暴露方式对溶栓有效的超声特性的影响。将人的血液放置24小时就可以形成血栓。将硅胶容器中含生理盐水的血凝块暴露在20至2000千赫的超声波中。无论超声频率和正弦、平方、“N”、正弦函数波形如何变化，超声暴露功率都保持在0.75w/cm^2的固定值。通过测量超声暴露起始和结束时血凝块的重量来评估溶栓量，通过激光束测量血栓周围血清透明度来持续观察溶栓速度。泵浦波是由近三个频率的超声开关构成的。结果：超声频率在200 ~ 250 kHz时溶栓效果最好，高于700 kHz时效果较差。有效频率还取决于血栓容器（即血管或器官）的尺寸和超声波长所决定的共振频率。当超声频率与该共振重合时，超声功率增强，空化形成，加速溶栓。形成快速负压的波形是通过空化产生的。在结构维数未知的体内环境中，由接近的三个频率组成的泵浦波也是有效的。

Ultrasound characters effective for thrombolysis have been studied on the appropriate frequency, wave mode and exposure mode. Thrombi have been made by leaving human blood for 24 hours. Blood clot with saline in the silicone container was exposed to ultrasound of 20 to 2000 kHz. The exposure power of ultrasound was kept to a fixed value of 0.75w/cm^2 despite the changes of ultrasound frequency and wave form of sin, square, "N" and sine function. The amount of thrombolysis was evaluated by measuring the weight of blood clot at the initial and ending time of ultrasound exposure, and the speed of thrombolysis was continuously observed by measuring transparency of serum around thrombus with laser beam. Pumping wave was constructed by switching ultrasound of close three frequencies. Result : Ultrasonic frequency of 200 to 250 kHz was most effective for thrombolysis and the frequencies higher than 700 kHz was less effective. The effective frequency also depends on resonance frequency determined by dimension of container of thrombus, i.e., vessel or organ and ultrasonic wave-length. When ultrasound frequency coincides with this resonance, ultrasound power is augmented and cavitations develops, which accelerates thrombolysis. The wave form which develops rapid negative pressure is effective through production of cavitation. Pumping wave composed of close three frequencies are also effective in in-vivo environment of unknown structural dimension.