DIELECTRIC PROPERTIES OF BRAIN-TISSUE BETWEEN 0.01 AND 10 GHZ
DIELECTRIC PROPERTIES OF BRAIN-TISSUE BETWEEN 0.01 AND 10 GHZ
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DOI：
10.1088/0031-9155/24/6/008
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发表时间：
1979-01-01
影响因子：
3.5
通讯作者：
SCHWAN, HP
中科院分区：
文献类型：
--
作者：
FOSTER, KR;SCHEPPS, JL;SCHWAN, HP
据报道，狗脑组织灰质和白质的介电常数和电导率在0.01和10 G[千兆赫]Hz之间。在0.01和。apprx之间。1 GHz时，介电常数减小，电导率随频率幂律增大。在1 GHz以上，由于组织中游离H2O分子偶极重取向，电导率随频率呈二次增长；旋转松弛频率为37度。C为21-24 GHz，略低于该温度下纯水的25 GHz特征频率。用麦克斯韦混合理论对微波数据进行了分析，该理论适用于非导电低介电常数球在水体中的悬浮。从1 GHz以上电导率的增加和2-4 GHz的组织介电常数来看，灰质和白质中H2O的表观体积分数分别约为0.70和0.55，比文献中各自的值低约10-15%。这种差异显然是由于水的一小部分，它不贡献组织介电常数bbb1ghz。给出了经验方程，总结了平均脑组织在37度时的介电特性。C为今后头部微波吸收的理论研究奠定基础。
Dielectric permittivity and conductivity are reported for gray and white matter from dog brain tissue between 0.01 and 10 G[giga]Hz. Between 0.01 and .apprx. 1 GHz, the permittivity decreases and conductivity increases as a power law of frequency. Above 1 GHz, the conductivity increases quadratically with frequency due to dipolar reorientation of free H2O molecules in tissue; the apparent rotational relaxation frequency at 37.degree. C is 21-24 GHz, slightly below the 25 GHz characteristic frequency of pure H2O at that temperature. The microwave data are analyzed using the Maxwell mixture theory applicable for a suspension of nonconducting, low permittivity spheres in bulk H2O. From the increase in conductivity above 1 GHz, and the tissue permittivity at 2-4 GHz, the apparent volume fraction of H2O is approximately 0.70 and 0.55 for gray and white matter, respectively, about 10-15% lower than respective values from the literature. This discrepancy is apparently due to a small fraction of H2O which does not contribute to the tissue permittivity > 1 GHz. Empirical equations are given to summarize the dielectric properties of average brain tissue at 37.degree. C for future theoretical studies of microwave absorption in the head.