细胞和组织射频介电弛豫特性分析

Analysis of Dielectric Relaxation Properties of Cells and Tissues at Radio Frequencies

本文分析了人血红细胞悬液、人脑胶质瘤和周围组织样本在５～５００ＭＨｚ频率范围的射频介电弛豫特性。介电数据由轴传输线反射法生物介电测量系统测量得出。描述介电弛豫分布性质的Ｃｏｌｅ－Ｃｏｌｅ非线性方程，有五个拟合参数：中心弛豫频率ｆｃ、远离ｆｃ的静态介电常数εｓ和高频介电常数ε∞、弛豫分布参数α、静态电导率σｓ。不同年龄组的人血红细胞悬液样本，ｆｃ接近，说明其介电弛豫机制相似，介电差异主要表现在σｓ和ε∞上，高年龄的比低年龄的小。用复数阻抗率的虚部关于实部作图表征方式使红细胞介电弛豫特性更加直观。脑肿瘤组织的α比周围组织的小，归因于前者结构分化小，从而弛豫时间的分布比较集中；前者的ｆｃ高出后者的４倍多，表明两者吸收电磁能的频率选择性；损耗角正切ｔｇδ表征电热能量转换的量度，在１５～５００ＭＨｚ频率区域，脑肿瘤组织的ｔｇδ较大，１００ＭＨｚ左右的入射电磁波对周缘正常组织的损伤相对较小，频率选择性吸收对电磁波治癌的临床方案制定有实用指导意义。

he dielectric relaxation properties were analysed for human red blood cells (RBC)in suspension and human glioma andsurrounding tissues at radio frequencies from 5～500MHz. The dielectric data were obtained from the biological dielectric measure-ments based on the method of coaxial transmission line reflection with a computerized network analyzer. The dielectric propertiesare represented by the non-liear Cole-Cole equation with five parameters including center relaxation frequency(fc) , the limitingpermittivity values at frequencies respectively far below and far above fc(εs and ε∞), relaxation spread parameter a,and the con-ductivity at low frequency(σs).The relaxation mechanism of RBC samples from volunteers in different ages is similar to the valuesof fc and less changed,therewithal the main dielectric differences are reflected in σs and ε∞ with larger values in higher ages. Therelaxation processes of RBC can be described more obviously with the specific imlredance diagram. The a value of brain tumour islarger than that of surrounding tissue due to less structure differentiation in the former,resuled in the narrow spread of relaxationtimes. The tumour has fc 4 times higher than that of the surrounding tissue to indicate a difference of frequency dependence be-tween both relaxations, while the loss tangent(tgδ)gives the level of electrical-thermal energy transformation. In the frequencyrange of between 15～500MHz,tumour tissue has a higher tgδ with the maximum at around 100 MHz. The results of a selectiveaborbtion of frequency dependence supply were useful information for clinical application of radio frequency electromagnetic irradi-ation for the hyperthermia of human brain tumours.