Schneider C, Van Dijk J D
Department of Radiotherapy, University of Amsterdam, The Netherlands.
Int J Hyperthermia. 1991 Mar-Apr;7(2):355-66. doi: 10.3109/02656739109005001.
A simple, unique tool has been constructed at a very low cost for visualization of the electric field distribution in a phantom exposed to radiofrequency fields from a four-applicator hyperthermia system. The tool consists of a thin Perspex plate to which light-emitting diodes (LEDs) have been attached in a regular pattern. The leads of these LEDs have been bent in the form of dipoles. Electric field distributions can be made visible, because the light intensity from an individual LED dipole in a RF field is a function of the local electric field strength. The LED dipoles were arranged in a 11 x 15 matrix with a mutual distance of 2 cm. Experiments have been performed in a cylinder with a length of 100 cm and with an elliptical cross-section of 24 cm x 36 cm. The cylinder was filled with saline to simulate the electric properties of biological tissue. The matrix plate was shaped like the cross-section inside the phantom, and could be moved to any position under the externally applied antennae. In our department the applicators installed form a system of four coherent waveguide radiators operating at a frequency of 70 MHz. Photographs have been taken from the distribution of the light intensity through transparent windows at the outer ends of the phantom. The advantage of the LED matrix is the fact that the effect of changing phase relations, amplitudes or position of any applicator on the electric field distribution can be seen instantaneously. The interference effects of multiple fields, i.e. extinction and reinforcement, become easily visible. Typical examples demonstrate the necessity to obtain the field distribution not only along some previously chosen lines, but in the whole transversal midplane. The attenuation of field strength due to the presence of the matrix varies only slightly from the edge to the centre of the matrix, so the pattern of light intensity is in good qualitative agreement with the pattern of field strength. The LED matrix has been very useful in the verification of pretreatment planning calculations, and is already used for intercomparison and evaluation studies of similar hyperthermia equipment.
我们以非常低的成本构建了一种简单、独特的工具，用于可视化置于四辐射器热疗系统射频场中的体模内的电场分布。该工具由一块薄有机玻璃板组成，发光二极管（LED）以规则模式附着其上。这些LED的引脚被弯成偶极子的形式。由于射频场中单个LED偶极子发出的光强度是局部电场强度的函数，因此电场分布可以变得可见。LED偶极子排列成一个11×15的矩阵，相互间距为2厘米。实验是在一个长度为100厘米、椭圆形横截面为24厘米×36厘米的圆柱体中进行的。圆柱体内充满盐水以模拟生物组织的电学特性。矩阵板的形状与体模内部的横截面相同，可以移动到外部施加天线下方的任何位置。在我们科室，所安装的辐射器构成了一个由四个相干波导辐射器组成的系统，工作频率为70兆赫兹。通过体模外端的透明窗口拍摄了光强度分布的照片。LED矩阵的优点在于，任何辐射器的相位关系、幅度或位置变化对电场分布的影响都能即时显现。多个场的干涉效应，即消光和增强，很容易被观察到。典型例子表明，不仅需要沿着一些预先选定的线获取场分布，还需要在整个横向中平面获取。由于矩阵的存在导致的场强衰减从矩阵边缘到中心仅略有变化，因此光强度模式与场强模式在定性上吻合良好。LED矩阵在预处理计划计算的验证中非常有用，并且已经用于类似热疗设备的相互比较和评估研究。
