Chowdhury D Q, Hill S C
Department of Applied Physics, Yale University, New Haven, CT 06520.
IEEE Trans Biomed Eng. 1991 Dec;38(12):1246-55. doi: 10.1109/10.137290.
Numerically optimized SAR (specific absorption rate) distributions in a source free 3-D multilayered concentric cylindrical (MCC) model are presented. The fields were expanded in the modes of the MCC. Cost functions which specify mathematically the relative weight assigned to differences between an SAR distribution and a desired SAR distribution were defined. The coefficients of the modes, which minimize the cost function, were obtained using gradient search optimization methods. The optimized SAR distributions shown were computed using three different cost functions and two different radial locations for the center of the region where the desired SAR is largest. A five-layered model, including the outer water layer for cooling and improved matching with the source, was used. The frequency was 70 MHz. The current and charge distributions computed on a perfectly conducting cylindrical surface just outside the model are also shown. The surface current and charge distributions depend strongly on the relative importance of the cost for acute heat and systemic heat. A technique is developed for generating a new set of basis functions for reducing the number of unknowns to be optimized. We suggest that the approach shown could be useful in designing hyperthermia applicators.
本文给出了在无源三维多层同心圆柱（MCC）模型中通过数值优化得到的比吸收率（SAR）分布。场以MCC的模式展开。定义了成本函数，该函数从数学上指定了赋予SAR分布与期望SAR分布之间差异的相对权重。使用梯度搜索优化方法获得使成本函数最小化的模式系数。所示的优化SAR分布是使用三种不同的成本函数以及期望SAR最大区域中心的两个不同径向位置计算得出的。使用了一个五层模型，包括用于冷却和改善与源匹配的外层水层。频率为70MHz。还展示了在模型外部刚好在完美导电圆柱表面上计算出的电流和电荷分布。表面电流和电荷分布强烈依赖于急性热成本和全身热成本的相对重要性。开发了一种生成新的基函数集的技术，以减少待优化未知数的数量。我们认为所示方法可能对设计热疗施源器有用。
