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

在合适的频率、波型和照射方式下，研究了有效溶栓的超声特性。血栓是通过放置人类血液24小时而形成的。硅胶容器中含有生理盐水的血液凝块暴露于20~2000 kHz的超声波中。改变超声频率和正弦、方波、“N”波和正弦波的波形，超声的曝光功率保持在0.75w/cm2的固定值。通过测量超声照射开始和结束时的血栓重量来评价溶栓量，通过激光测量血栓周围血清的透明度来连续观察溶栓速度。通过切换接近三个频率的超声来构造泵浦波。结果：超声频率为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的大小，即血管或器官的大小和超声波长所确定的共振频率。当超声频率与这种共振相一致时，超声功率增大，空化形成，从而加速血栓溶解。形成快速负压的波形是通过产生空化而有效的。由接近三个频率组成的泵浦波在结构尺寸未知的体内环境中也是有效的。

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.