IEEE Trans Biomed Eng. 2021 Jan;68(1):90-98. doi: 10.1109/TBME.2020.2996825. Epub 2020 Dec 21.
To investigate the thermal and frequency dependence of dielectric properties of ex vivo liver tissue - relative permittivity and effective conductivity - over the frequency range 500 MHz to 6 GHz and temperatures ranging from 20 to 130 °C.
We measured the dielectric properties of fresh ex vivo bovine liver tissue using the open-ended coaxial probe method (n = 15 samples). Numerical optimization techniques were utilized to obtain parametric models for characterizing changes in broadband dielectric properties as a function of temperature and thermal isoeffective dose. The effect of heating tissue at rates over the range 6.4-16.9 °C/min was studied. The measured dielectric properties were used in simulations of microwave ablation to assess changes in simulated antenna return loss compared to experimental measurements.
Across all frequencies, both relative permittivity and effective conductivity dropped sharply over the temperature range 89 - 107 °C. Below 91 °C, the slope of the effective conductivity changes from positive values at lower frequencies (0.5-1.64 GHz) to negative values at higher frequencies (1.64-6 GHz). The maximum achieved correlation values between transient reflection coefficients from measurements and simulations ranged between 0.83 - 0.89 and 0.68 - 0.91, respectively, when using temperature-dependent and thermal-dose dependent dielectric property parameterizations.
We have presented experimental measurements and parametric models for characterizing changes in dielectric properties of bovine liver tissue at ablative temperatures.
The presented dielectric property models will contribute to the development of ablation systems operating at frequencies other than 2.45 GHz, as well as broadband techniques for monitoring growth of microwave ablation zones.
研究离体猪肝组织的介电特性（相对介电常数和有效电导率）在 500MHz 至 6GHz 的频率范围内和 20 至 130°C 的温度范围内的热频依赖性。
我们使用开口同轴探头法（n = 15 个样本）测量了新鲜离体牛肝组织的介电特性。利用数值优化技术，获得了参数模型，用于描述宽带介电特性随温度和热等效应剂量的变化。研究了以 6.4-16.9°C/min 的速率加热组织的效果。利用测量得到的介电特性对微波消融模拟进行了仿真，以评估与实验测量相比，模拟天线回波损耗的变化。
在所有频率下，相对介电常数和有效电导率在 89-107°C 的温度范围内急剧下降。在 91°C 以下，有效电导率的斜率在较低频率（0.5-1.64GHz）下为正值，在较高频率（1.64-6GHz）下为负值。当使用依赖于温度和依赖于热剂量的介电特性参数化时，测量和模拟的瞬态反射系数之间的最大相关值分别在 0.83-0.89 和 0.68-0.91 之间。
我们提出了用于表征在消融温度下牛肝组织介电特性变化的实验测量和参数模型。
所提出的介电特性模型将有助于开发在 2.45GHz 以外频率工作的消融系统，以及用于监测微波消融区域生长的宽带技术。
