Hynynen K
Arizona Cancer Center, University of Arizona Health Sciences Center, Tucson 85724.
Med Phys. 1991 Nov-Dec;18(6):1156-63. doi: 10.1118/1.596626.
In this study the feasibility of utilizing nonlinear ultrasound propagation to control the power deposition patterns during ultrasound hyperthermia treatments of malignant tumors was investigated. From the in vivo results it appears that the power deposition pattern and the temperature distributions can be significantly altered by increasing the temporal peak power of the source while reducing the duty cycle to maintain the same acoustic time average power. The maximum temperature gains obtained during hyperthermia sonication (between 1.5 and 2) were significantly less than one could obtain by varying the frequency and the other parameters of transducers and thus, the linear characteristics of the ultrasound fields should be used when hyperthermia systems are designed and treatments are planned. Then during the treatment nonlinear propagation can be used to provide on-line control of the power deposition patterns. The transducer characteristics determined the magnitude of the temperature gain and the nonlinear propagation region could not be reached when sharply focused (F number = 1) transducers were used at the frequencies between 0.25 to 1.68 MHz due to the high pressure amplitudes that exceeded the transient cavitation threshold.
在本研究中，对利用非线性超声传播来控制恶性肿瘤超声热疗过程中的功率沉积模式的可行性进行了研究。从体内实验结果来看，通过提高源的时间峰值功率同时降低占空比以保持相同的声时平均功率，功率沉积模式和温度分布可被显著改变。热超声处理过程中获得的最大温度升高（在1.5至2之间）明显小于通过改变换能器的频率和其他参数所能获得的升高，因此，在设计热疗系统和规划治疗方案时应采用超声场的线性特性。然后在治疗过程中，可利用非线性传播来对功率沉积模式进行在线控制。换能器特性决定了温度升高的幅度，当在0.25至1.68MHz频率下使用锐聚焦（F数=1）换能器时，由于高压幅值超过了瞬态空化阈值，无法达到非线性传播区域。
