Dielectric properties of mammalian brain tissue between 1 and 18 GHz

A newly developed frequency domain technique was used to measure the dielectric properties of white matter, grey matter and macerated rabbit brain at 20 and 37 degrees C. An analysis of the data showed that between 1 and 4 GHz there were substantial contributions from processes other than the gamma dispersion. However, above 7.5 GHz it appeared that mainly free water was relaxing although evidence of a small spread of relaxation times was found for the bulk water in the white matter. Mouse and rat brain were also measured but no significant differences were found between the species. The quantity of bound water was estimated but there was no evidence of a difference in the amount between either the tissues or the temperatures.     

Dielectric properties of female human breast tissue measured in vitro at 3.2 GHz.

Complex permittivities of in vitro diseased and undiseased human female breast tissues have been measured at 3.2 GHz using a resonant cavity technique. Ranges of dielectric properties and water contents of these tissues are presented. Experimental data are compared with models predicted from mixture equations. Measured permittivity data lie within limits set by two-phase mixture theory, but some conductivity data are in excess of those expected for a mixture of saline and protein. At any particular microwave frequency in all tissue of a given type, the relationship between permittivity and conductivity may be parametrized using the Debye relaxation equations. For each breast tissue type a characteristic relaxation frequency was calculated and found to be lower than that of physiological saline at the same temperature. It is concluded that the dielectric relaxation of tissue water is not the only dispersive process occurring at this frequency: dielectric relaxation of bound water and the tail end of a beta-dispersion may also contribute to the dielectric properties. The similarity of the dielectric properties of benign and malignant breast tumours measured in this work suggest that in vivo dielectric imaging methods will not be capable of distinguishing them.     

Dielectric properties of Co-gamma-irradiated and microwave-heated rat tumour and skin measured in vivo between 0.2 and 2.4 GHz

The dielectric properties of a rat tumour (rhabdomyosarcoma R1H), skin and muscle were measured in vivo with an open-ended coaxial line and a computer-controlled system based on a network analyser. The permittivity of the tumour R1H and of the normal tissues in anaesthetised rats was determined at frequencies between 0.2 and 2.4 GHz. No significant differences were observed either between rat tumour and muscle or between normal and 15 Gy irradiated rat tumour and skin. However, after a hyperthermia treatment at 43 degrees C for 60 min the dielectric properties, especially of the rat skin, changed due to the hyperthermic induced oedema which is related to an increase in tissue water content. The process of the oedema modifies the dielectric properties of the skin to a higher degree than those of the tumour.     

Dielectric properties of biological tissue at low temperatures demonstrated on fatty tissue.

Dielectric behaviour of fatty tissue was investigated from T = 300 K to 4 K and f = 20 Hz to 1 MHz. Characteristic curves were obtained only at low frequencies. With decreasing temperature four important features were detected: the water-ice transition at T = 265 K, a relaxation process of the fat molecules (near 260 K) and one connected with the ice-part (210 K-170 K). The reason for the fourth relaxation at T = 140 K has not been fully understood yet: it may be caused by segmental rotation of the fatty acid molecules or the presence of multiple bonds. The epsilon"-maximum caused by the ice relaxation at T congruent to 200 K can be used to detect successful application of cryotherapy, i.e. the temperature fall below the minimum value of 233 K.     

MRI拉莫尔频率范围内人体脑胶质瘤组织的介电特性

目的:研究人体脑胶质瘤组织在MRI拉莫尔频率范围内（50~500 MHz）的介电特性,建立人体脑胶质瘤组织介电参数频率谱图,为磁共振断层成像技术提供理论依据和数据参考。方法:以神经外科手术中切下的脑胶质瘤组织为标本,在温度为37 °C的恒温水箱中,利用开端同轴线法,在50~500 MHz频率范围内使用AV 3656A网络分析仪测量脑胶质瘤组织标本的介电特性。以四阶Cole-Cole模型为基础,利用最小二乘曲线拟合方法,提取人体脑胶质瘤组织的介电特征参数。同时,将实验测得的脑胶质瘤组织介电特性与健康人体组织介电特性数据库中的正常脑组织进行比较。结果:在测频率范围内,人体脑胶质瘤组织实测数据与Cole-Cole模型吻合良好,且有人体脑胶质瘤组织的相对介电常数比正常脑组织高29.5%~36.6%,电导率比正常脑组织高56.1%~64.8%。结论:本文报道了37 °C下人体脑胶质瘤组织在MRI拉莫尔频率范围内（50~500 MHz）的介电特性数据及相应的Cole-Cole模型介电特征参数,可为人体脑胶质瘤组织介电特性研究和磁共振断层成像技术提供基础数据。     

The dielectric properties of rabbit tissue, pure water and various liquids suitable for tissue phantoms at 35 GHz

Newly developed microwave apparatus was used to measure the complex permittivity of some rabbit tissues and water over the temperature range 20-37 degrees C. Various liquid mixtures which might be suitable as phantom tissue equivalents at 35 GHz were also considered. Some of the measured tissue data were compared with previous lower frequency data and it was concluded that the observed behaviour was not anomalous.     

Dielectric properties of human normal, malignant and cirrhotic liver tissue: in vivo and ex vivo measurements from 0.5 to 20 GHz using a precision open-ended coaxial probe

Hepatic malignancies have historically been treated with surgical resection. Due to the shortcomings of this technique, there is interest in other, less invasive, treatment modalities, such as microwave hepatic ablation. Crucial to the development of this technique is the accurate knowledge of the dielectric properties of human liver tissue at microwave frequencies. To this end, we characterized the dielectric properties of in vivo and ex vivo normal, malignant and cirrhotic human liver tissues from 0.5 to 20 GHz. Analysis of our data at 915 MHz and 2.45 GHz indicates that the dielectric properties of ex vivo malignant liver tissue are 19 to 30% higher than normal tissue. The differences in the dielectric properties of in vivo malignant and normal liver tissue are not statistically significant (with the exception of effective conductivity at 915 MHz, where malignant tissue properties are 16% higher than normal). Also, the dielectric properties of in vivo normal liver tissue at 915 MHz and 2.45 GHz are 16 to 43% higher than ex vivo. No statistically significant differences were found between the dielectric properties of in vivo and ex vivo malignant tissue (with the exception of effective conductivity at 915 MHz, where malignant tissue properties are 28% higher than normal). We report the one-pole Cole-Cole parameters for ex vivo normal, malignant and cirrhotic liver tissue in this frequency range. We observe that wideband dielectric properties of in vivo liver tissue are different from the wideband dielectric properties of ex vivo liver tissue, and that the in vivo data cannot be represented in terms of a Cole-Cole model. Further work is needed to uncover the mechanisms responsible for the observed wideband trends in the in vivo liver data.     

The sorptive properties of brain tissue in newborn and adult rats

Summary The sorption properties of the brain were determined in newborn ratlings, in adult intact and adrenalectomized rats after administration of the same dose of neutral red (per gm of body weight). The data obtained with the aid of photocolorimetry show that the sorption faculty of the newborns is three times lower than that in adult rats, whele adrenalectomy does not change the sorption properties of the brain in adult rats. This investigation confirms the conclusions of the previous author's works according to which increased Medinal content in the brain of the newborn ratlings is a result of increased permeability of the hematoencephalic barrier.(Presented by AMN SSSR Active Member V. M. Karasik) Translated from Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 52, No. 8, pp. 111–112, August, 1961     

Mechanical properties of brain tissue by indentation: Interregional variation

Although many studies on the mechanical properties of brain tissue exist, some controversy concerning the possible differences in mechanical properties of white and gray matter tissues remains. Indentation experiments are conducted on white and gray matter tissues of various regions of the cerebrum and on tissue from the thalamus and the midbrain to study interregional differences. An advantage of indentation, when compared to standard rheological tests as often used for the characterization of brain tissue, is that it is a local test, requiring only a small volume of tissue to be homogeneous. Indentation tests are performed at different speeds and the force relaxation after a step indent is measured as well. White matter tissue is found to be stiffer than gray matter and to show more variation in response between different samples which is consistent with structural differences between white matter and gray matter. In addition to differences between white matter and gray matter, also different regions of brain tissue are compared.     

Dielectric properties of low-water-content tissues

The dielectric properties of two low-water-content tissues, bone marrow and adipose tissue, were measured from 1 kHz to 1 GHz. From 1 kHz to 13 MHz, the measurements were performed using a parallel-plate capacitor method. From 10 MHz to 1 GHz, a reflection coefficient technique using an open-ended coaxial transmission line was employed. The tissue water contents ranged from 1 to almost 70% by weight. The dielectric properties correlate well with the values predicted by mixture theory. Comparison with previous results from high-water-content tissues suggests that bone marrow and adipose tissues contain less motionally altered water per unit dry volume than do the previously studied tissues with lower lipid fractions. The high degree of structural heterogeneity of these tissues was reflected in the large scatter of the data, a source of uncertainty that should be considered in practical applications of the present data.     

脑组织钙,钙调素与兔感染性脑水肿关系的探讨

采用百日咳菌液右侧颈内动脉注射造成家兔急性感染性脑水肿（ＢＥ），测定不同时间脑组织水、钙、钙调素（ＣａＭ）含量，注射菌液后１ｈ，右侧脑组织水、钙含量均已明显增高（Ｐ〈０．０１），脑组织ＣａＭ含量也相应增高，注射菌液后２ｈ，其含量较对照组差异具有显著性意义（Ｐ〈０．０５），ＢＥ的发展与脑组织钙与ＣａＭ变化均呈正相关（ｒ＝０．８９０２，ｒ＝０．７９２５，Ｐ〈０．０１）。结果显示：脑组织钙聚积和ＣａＭ活     

Dielectric relaxation properties of linear polythioethers

Values of the dielectric loss tangent were obtained as a function of temperature for poly(pentamethylene sulfide) (P5MS) and poly(1,3-dithiocane) (PDTC). Both P5MS and PDTC exhibit a β absorption, located in the vicinity of their respective glass transition temperatures, ?105°C and ?73°C, which is believed to be associated with micro-Brownian motions in the amorphous phase of the crystalline polymers. The glass-rubber transitions of the polymers are discussed in terms of the flexibility of the chains, as expressed by their conformational partition functions and entropies.     

Age dependence of dielectric properties of bovine brain and ocular tissues in the frequency range of 400 MHz to 18 GHz

In order to identify possible age-dependent dielectric properties of brain and eye tissues in the frequency range of 400 MHz to 18 GHz, measurements on bovine grey and white matter as well as on cornea, lens (cortical) and the vitreous body were performed using a commercially available open-ended coaxial probe and a computer-controlled vector network analyser. Freshly excised tissues of 52 animals of two age groups (42 adult animals, i.e. 16-24 month old and 10 young animals, i.e. 4-6 month old calves) were examined within 8 min (brain tissue) and 15 min (eye tissue), respectively, of the animals' death. Tissue temperatures for the measurements were 32+/-1 degrees C and 25+/-1 degrees C for brain and eye tissues, respectively. Statistical analysis of the measured data revealed significant differences in the dielectric properties of white matter and cortical lens tissue between the adult and the young group. In the case of white matter the mean values of conductivity and permittivity of young tissue were 15%-22% and 12%-15%, respectively, higher compared to the adult tissue in the considered frequency range. Similarly, young cortical lens tissue was 25%-76% higher in conductivity and 27%-39% higher in permittivity than adult cortical lens tissue.     

Complex dielectric constant of arginine-DNA and protamine-DNA aqueous systems at 10 GHz

The complex dielectric constant of arginine and protamine from herring sperm (clupeine) and their complexes with herring sperm DNA was measured at 10 GHz in the temperature range -20 to +45 degrees C by a microwave cavity perturbation method. The experimental results were analysed in terms of a three-component equation (solute molecules, interfacial water and bulk water) to calculate the fractional volume of modified water and hence the specific hydration of the samples. A fourfold reduction of the specific hydration is observed for the clupeine molecule as compared to the free monomers. This is consistent with a folded conformation of the protein in solution. The specific hydration of the complex between clupeine and DNA is reduced by 50% with respect to the weighted average for the uncomplexed components. This result indicates an intimate contact between clupeine and DNA with exclusion of water molecules and is consistent with the highly condensed form of nucleoprotamines which is known in vivo.     

In vitro determination of normal and neoplastic human brain tissue optical properties using inverse adding-doubling

To complement a project towards the development of real-time optical biopsy for brain tissue discrimination and surgical resection guidance, the optical properties of various brain tissues were measured in vitro and correlated to features within clinical diffuse reflectance tissue spectra measured in vivo. Reflectance and transmission spectra of in vitro brain tissue samples were measured with a single-integrating-sphere spectrometer for wavelengths 400-1300 nm and converted to absorption and reduced scattering spectra using an inverse adding-doubling technique. Optical property spectra were classified as deriving from white matter, grey matter or glioma tissue according to histopathologic diagnosis, and mean absorption and reduced scattering spectra were calculated for the three tissue categories. Absolute reduced scattering and absorption values and their relative differences between histopathological groups agreed with previously reported results with the exception that absorption coefficients were often overestimated, most likely due to biologic variability or unaccounted light loss during reflectance/transmission measurement. Absorption spectra for the three tissue classes were dominated by haemoglobin absorption below 600 nm and water absorption above 900 nm and generally determined the shape of corresponding clinical diffuse reflectance spectra. Reduced scattering spectral shapes followed the power curve predicted by the Rayleigh limit of Mie scattering theory. While tissue absorption governed the shape of clinical diffuse reflectance spectra, reduced scattering determined their relative emission intensities between the three tissue categories.