Tanter M, Thomas J L, Fink M
Laboratoire Ondes et Acoustique, ESPCI, Université Paris VII, U.R.A. C.N.R.S. 1503, France.
J Acoust Soc Am. 1998 May;103(5 Pt 1):2403-10. doi: 10.1121/1.422759.
The time-reversal process is applied to focus pulsed ultrasonic waves through the human skull bone. The aim here is to treat brain tumors, which are difficult to reach with classical surgery means. Such a surgical application requires precise control of the size and location of the therapeutic focal beam. The severe ultrasonic attenuation in the skull reduces the efficiency of the time reversal process. Nevertheless, an improvement of the time reversal process in absorbing media has been investigated and applied to the focusing through the skull [J.-L. Thomas and M. Fink, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 43, 1122-1129 (1996)]. Here an extension of this technique is presented in order to focus on a set of points surrounding an initial artificial source implanted in the tissue volume to treat. From the knowledge of the Green's function matched to this initial source location a new Green's function matched to various points of interest is deduced in order to treat the whole volume. In a homogeneous medium, conventional steering consists of tilting the wave front focused on the acoustical source. In a heterogeneous medium, this process is only valid for small angles or when aberrations are located in a layer close to the array. It is shown here how to extend this method to aberrating and absorbing layers, like the skull bone, located at any distance from the array of transducers.
时间反转过程被应用于通过人类颅骨聚焦脉冲超声波。其目的是治疗脑肿瘤，而传统手术方法难以触及这些肿瘤。这种手术应用需要精确控制治疗聚焦束的大小和位置。颅骨中严重的超声衰减降低了时间反转过程的效率。尽管如此，人们已经研究了吸收介质中时间反转过程的改进方法，并将其应用于通过颅骨的聚焦[J.-L. 托马斯和M. 芬克，《IEEE超声、铁电与频率控制汇刊》43, 1122 - 1129 (1996)]。这里提出了该技术的一种扩展，以便聚焦于围绕植入待治疗组织体积中的初始人工源的一组点。根据与该初始源位置匹配的格林函数的知识，推导出与各个感兴趣点匹配的新格林函数，以便治疗整个体积。在均匀介质中，传统的转向包括倾斜聚焦于声源的波前。在非均匀介质中，此过程仅在小角度或像颅骨这样的像差位于靠近阵列的层中时才有效。这里展示了如何将此方法扩展到位于距换能器阵列任意距离处的像颅骨这样的像差和吸收层。
