Fan X, Hynynen K
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Med Phys. 1995 Mar;22(3):297-306. doi: 10.1118/1.597603.
Focused high-power ultrasound beams are well suited for noninvasive local destruction of deep target volumes. In order to avoid cavitation and to utilize only thermal tissue damage, high frequencies (1-5 MHz) are used in ultrasonic surgery. However, the focal spots generated by sharply focused transducers become so small that only small tumors can be treated in a reasonable time. Phased array ultrasound transducers can be employed to electronically scan a focal spot or to produce multiple foci in the desired region to increase the treated volume. In this article, theoretical and experimental studies of spherically curved square-element phased arrays for use in ultrasonic surgery were performed. The simulation results were compared with experimental results from a 16-element array. It was shown that the phased array could control the necrosed tissue volume by using closely spaced multiple foci. The phased array can also be used to enlarge a necrosed tissue volume in only one direction at a time, i.e., lateral or longitudinal. The spherically curved 16 square-element phased array can produce useful results by varying the phase and amplitude setting. Four focal points can be easily generated with a distance of two or four wavelengths between the two closest peaks. The maximum necrosed tissue volume generated by the array can be up to sixteen times the volume induced by a similar spherical transducer. Therefore the treatment time could be reduced compared with single transducer treatment.
聚焦的高功率超声束非常适合对深部目标区域进行无创局部破坏。为了避免空化现象并仅利用热组织损伤，超声手术中使用高频（1 - 5兆赫）。然而，由锐聚焦换能器产生的焦斑变得非常小，以至于在合理时间内只能治疗小肿瘤。相控阵超声换能器可用于电子扫描一个焦斑或在所需区域产生多个焦点，以增加治疗体积。在本文中，对用于超声手术的球形弯曲方形元件相控阵进行了理论和实验研究。将模拟结果与来自一个16元件阵列的实验结果进行了比较。结果表明，相控阵可通过使用紧密间隔的多个焦点来控制坏死组织体积。相控阵还可用于一次仅在一个方向（即横向或纵向）扩大坏死组织体积。球形弯曲的16方形元件相控阵通过改变相位和幅度设置可产生有用的结果。两个最接近峰值之间的距离为两个或四个波长时，可轻松产生四个焦点。该阵列产生的最大坏死组织体积可达类似球形换能器诱导体积的十六倍。因此，与单换能器治疗相比，治疗时间可缩短。
