Shaw J A, Durney C H, Christensen D A
Department of Electrical Engineering, University of Utah, Salt Lake City 84112.
IEEE Trans Biomed Eng. 1991 Sep;38(9):861-70. doi: 10.1109/10.83606.
A hyperthermia applicator design tool consisting of a finite-difference time-domain (FDTD) technique in combination with a graphical display of electric fields and normalized linear temperature rise is described. This technique calculates, rather than assumes, antenna current distributions; it includes mutual interactions between the body and the applicator, and it calculates driving-point impedance and power delivered to the applicator. Results show that the fundamental limitation of 2-D electric-type applicators is overheating of the fat by normal components of the electric field, which exist because of near fields and capacitive coupling with the muscle. Two factors which contribute to the capacitance are the muscle conductivity and the small antenna size in air. Two examples of applicators designed to avoid fat overheating are described: a 27-MHz segmented dipole for heating large tumors to 7 cm depth, and a 100-MHz dipole for small tumors to 5 cm depth. The first uses a water bolus, and the second uses a water bolus with low-permittivity strips to reduce normal fields at the antenna ends. The results of this study describe fundamental limitations of electric field applicators, and illustrate the use of a powerful applicator design tool that allows rapid evaluation of a wide range of ideas for applicators which would require months and years to test experimentally.
描述了一种热疗施加器设计工具，它由时域有限差分（FDTD）技术与电场图形显示和归一化线性温升相结合组成。该技术计算而不是假设天线电流分布；它包括人体与施加器之间的相互作用，并计算驱动点阻抗和输送到施加器的功率。结果表明，二维电型施加器的基本局限性在于电场的正常分量会导致脂肪过热，这是由于近场以及与肌肉的电容耦合而存在的。导致电容的两个因素是肌肉电导率和空气中天线尺寸较小。描述了两个旨在避免脂肪过热的施加器示例：一个用于将大肿瘤加热到7厘米深度的27兆赫兹分段偶极子，以及一个用于将小肿瘤加热到5厘米深度的100兆赫兹偶极子。第一个使用水垫，第二个使用带有低介电常数条带的水垫以减少天线端部的正常场。这项研究的结果描述了电场施加器的基本局限性，并说明了一种强大的施加器设计工具的使用，该工具允许快速评估各种施加器方案，而这些方案通过实验测试需要数月甚至数年时间。
