Dielectric properties of brain tissue between 0.01 and 10 GHz

Dielectric permittivity and conductivity are reported for grey and white matter from dog brain tissue between 0.01 and 10 GHz. Between 0.01 and approximately 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 water molecules in tissue; the apparent rotational relaxation frequency at 37 degrees C is 21--25 GHz, slightly below the 25 GHz characteristic frequency of pure water at that temperature. The microwave data are analysed using the Maxwell mixture theory applicable for a suspension of nonconducting, low permittivity spheres in bulk water. From the increase in conductivity above 1 GHz, and the tissue permittivity at 2--4 GHz, the apparent volume fraction of water is approximately 0.70 and 0.55 for grey and white matter, respectively, about 10--15% lower than respective values from the literature. This discrepancy is apparently due to a small fraction of water which does not contribute to the tissue permittivity above 1 GHz. Empirical equations are given to summarise the dielectric properties of 'average' brain tissue at 37 degrees C for future theoretical studies of microwave absorption in the head.     

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。     

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 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.     

Bulk optical properties of healthy female breast tissue

We have measured the bulk optical properties of healthy female breast tissues in vivo in the parallel plate, transmission geometry. Fifty-two volunteers were measured. Blood volume and blood oxygen saturation were derived from the optical property data using a novel method that employed a priori spectral information to overcome limitations associated with simple homogeneous tissue models. The measurements provide an estimate of the variation of normal breast tissue optical properties in a fairly large population. The mean blood volume was 34 +/- 9 microM and the mean blood oxygen saturation was 68 +/- 8%. We also investigated the correlation of these optical properties with demographic factors such as body mass index (BMI) and age. We observed a weak correlation of blood volume and reduced scattering coefficient with BMI: correlation with age, however, was not evident within the statistical error of these experiments. The new information on healthy breast tissue provides insight about the potential contrasts available for diffuse optical tomography of breast tumours.     

Dielectric properties of mammalian breast milk at radiofrequencies

The relative permittivity and AC conductivity of breast milk have been investigated in four different mammalian species, human, cow, goat and sheep, in the frequency range 0.1-100 MHz and at a room temperature of 26.5 +/- 0.5 degrees C. The results showed that the sheep milk exhibited the largest dielectric dispersion, followed in decreasing order by milks from the goat, cow and human. The dielectric data were fitted to the Debye and Cole-Cole structural equations and the fitted parameters have been presented for the different species. The curve-fitting analysis has shown that for all the milk samples the Cole-Cole model gave a better fit to the dielectric data than the Debye model, thus suggesting heterogeneity of structure in milk. On the basis of the Cole-Cole model, the relaxation times in the mammalian milks were found to be distributed about the mean values of 162 +/- 10, 171 +/- 9, 177 +/- 14 and 192 +/- 12 ns for human, cow, goat and sheep milks, respectively.     

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.     

Elastic properties of microstructural components of human bone tissue as measured by nanoindentation.

The elastic properties of several microstructural components of dry human vertebrae (T-12 and L-1) and tibiae have been investigated in the longitudinal and transverse directions using nanoindentation. The largest Young's modulus was that for the interstitial lamellae in the longitudinal direction (25.7 +/- 1.7 GPa). This was followed in decreasing order by osteons in the longitudinal direction (22.4 +/- 1.2 GPa), trabeculae in the longitudinal direction (19.4 +/- 2.3 GPa), an average over osteons and interstitial lamellae in the transverse direction [16.6 +/- 1.1 GPa (it was difficult to microstructurally distinguish osteons from interstitial lamellae in the transverse direction)], and trabeculae in the transverse direction (15.0 +/- 2.5 GPa). An ANOVA statistical analysis revealed that the values all are significantly different (p < 0.05). Since the elastic moduli in the longitudinal direction are all greater than in the transverse, measurable elastic anisotropies exist in the components. The hardnesses also varied among the microstructural components in the range 0.52-0.74 GPa.     

Pleomorphic adenoma of the human female breast.

We are presenting an interesting rare benign breast tumor which meets the characteristics of a salivary gland pleomorphic adenoma. The tumor was misdiagnosed during frozen section procedure, because several clusters, mainly composed of myoepithelial cells and surrounded by a chondroid matrix, were mistaken for cancerous blasts. Additionally the clinical and mammographic findings were very suspicious. Although this particular tumor is very infrequent, the pathologist should be aware of the difficulties in the differential diagnosis during frozen section and thus defer his final answer to the paraffin sections.     

Bulk optical properties and tissue components in the female breast from multiwavelength time-resolved optical mammography

We present the results of a clinical study about optical properties and bulk composition of the female breast. The clinical study involved more than 150 subjects that underwent optical mammography. A multiwavelength time-resolved mammograph designed to collect time-resolved transmittance images of the breast at different wavelengths in the range 637 to 980 nm is used to this purpose. From the absorption spectrum of the breast, the concentrations of the main tissue constituents, i.e., oxygenated and deoxygenated hemoglobin, lipid, and water, are obtained for a subset of 113 breasts. The lipid content of breast is estimated for the first time on such a large number of subjects. The total hemoglobin concentration, blood oxygen saturation, lipid, and water content of breast is correlated to demographic information collected during the trial. As expected, breast optical properties and components undergo huge variations among different subjects. Different constituents, however, show interesting correlation with clinical parameters such as age, breast size, body mass index, and mammographic parenchymal pattern. These results suggest that optical measurements on breasts can be exploited to obtain relevant information on breast tissue composition.     

T1 and T2 temperature dependence of female human breast adipose tissue at 1.5 T: groundwork for monitoring thermal therapies in the breast

The T₁ and T₂ temperature dependence of female breast adipose tissue was investigated at 1.5 T in order to evaluate the applicability of relaxation‐based MR thermometry in fat for the monitoring of thermal therapies in the breast. Relaxation times T₁, T₂ and T_2TSE (the apparent T₂ measured using a turbo spin echo readout sequence) were measured in seven fresh adipose breast samples for temperatures from 25 to 65 °C. Spectral water suppression was used to reduce the influence of the residual water signal. The temperature dependence of the relaxation times was characterized. The expected maximum temperature measurement errors based on average calibration lines were calculated. In addition, the heating–cooling reversibility was investigated for two samples. The T₁ and T_2TSE temperature (T) dependence could be fitted well with an exponential function of 1/T. A linear relationship between T₂ and temperature was found. The temperature coefficients (mean ± inter‐sample standard deviation) of T₁ and T_2TSE increased from 25 °C (dT₁/dT = 5.35 ± 0.08 ms/°C, dT_2TSE/dT = 3.82 ± 0.06 ms/°C) to 65 °C (dT₁/dT = 9.50 ± 0.16 ms/°C, dT_2TSE/dT = 7.99 ± 0.38 ms/°C). The temperature coefficient of T₂ was 0.90 ± 0.03 ms/°C. The temperature‐induced changes in the relaxation times were found to be reversible after heating to 65 °C. Given the small inter‐sample variation of the temperature coefficients, relaxation‐based MR thermometry appears to be feasible in breast adipose tissue, and may be used as an adjunct to proton resonance frequency shift (PRFS) thermometry in aqueous tissue (glandular + tumor). Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

In vitro dielectric properties of human tissues at radiofrequencies

In vitro permittivity measurements of excised human liver, spleen, kidney and cardiac muscle at frequencies from 10 kHz to 100 MHz are described. An end-of-the-line capacitive sensor and a computer-controlled network analyser HP 3577 were employed. The results were compared with human data reported by other investigators as well as with the animal (cat) data obtained earlier in this laboratory. It was found that the conductivity of most of the human tissues tested was significantly higher than that of the animal tissues for the test frequencies. The dielectric constants for human kidney and spleen are higher than the corresponding animal (cat) tissues at frequencies from 10 kHz to approximately 1 MHz and at around 100 MHz. However, the values for liver do not differ significantly between the two species in the same frequency range.     

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.     

Prostate tissue stiffness as measured with a resonance sensor system: a study on silicone and human prostate tissue in vitro

Prostate cancer is the most common form of cancer in men in Europe and in the USA. Some prostate tumours are stiffer than the surrounding normal tissue, and it could therefore be of interest to measure prostate tissue stiffness. Resonance sensor technology based on piezoelectric resonance detects variations in tissue stiffness due to a change in the resonance frequency. An impression-controlled resonance sensor system was used to detect stiffness in silicone rubber and in human prostate tissue in vitro using two parameters, both combinations of frequency change and force. Variations in silicone rubber stiffness due to the mixing ratio of the two components could be detected (p<0.05) using both parameters. Measurements on prostate tissue showed that there existed a statistically significant (MANOVA test, p<0.001) reproducible difference between tumour tissue (n=13) and normal healthy tissue (n=98) when studying a multivariate parameter set. Both the tumour tissue and normal tissue groups had variations within them, which were assumed to be related to differences in tissue composition. Other sources of error could be uneven surfaces and different levels of dehydration for the prostates. Our results indicated that the resonance sensor could be used to detect stiffness variations in silicone and in human prostate tissue in vitro. This is promising for the development of a future diagnostic tool for prostate cancer.     

Reconstructed human cornea produced in vitro by tissue engineering.

The aim of the present study was to produce a reconstructed human cornea in vitro by tissue engineering and to characterize the expression of integrins and basement membrane proteins in this reconstructed cornea. Epithelial cells and fibroblasts were isolated from human corneas (limbus or centre) and cultured on plastic substrates in vitro. Reconstructed human corneas were obtained by culturing epithelial cells on collagen gels containing fibroblasts. Histological (Masson's trichrome staining) and immunohistological (laminin, type VII collagen, fibronectin as well as beta1, alpha3, alpha4, alpha5, and alpha6 integrin subunits) studies were performed. Human corneal epithelial cells from the limbus yielded colonies of small fast-growing cells when cultured on plastic substrates. They could be subcultured for several passages in contrast to central corneal cells. In reconstructed cornea, the epithelium had 4-5 cell layers by the third day of culture; basal cells were cuboidal. The basement membrane components were already detected after 3 days of culture. Integrin stainings, except for the alpha4 integrin, were also positive after 3 days. They were mostly detected at the epithelium-stroma junction. Such in vitro tissue-engineered human cornea, which shows appropriate histology and expression of basement membrane components and integrins, provides tools for further physiological, toxicological and pharmacological studies as well as being an attractive model for gene expression studies.     

Effects of hyaluronan on the invasive properties of human breast cancer cells in vitro

Hyaluronan (HA) is a high molecular weight glycosaminoglycan present mostly in the extracellular matrix (ECM). HA binds to specific receptors such as CD44. Its production is increased at the tumour-stroma interface, including those in breast cancer tumours. It has been suggested that it facilitates invasion of tumour cells into the ECM by a hydrodynamic effect, or by altering tumour cell behaviour. Using in vitro tests we studied the effect of immobilized (iHA) and soluble (sHA) HA on the invasive properties of four human breast cancer cell lines with different levels of CD44 expression. Our results show that iHA acts as an adhesive, haptotactic, and motility stimulating factor for the CD44 positive Hs578T cells and induces the expression of membrane CD44. sHA also changes the motility properties of the Hs578T and MDA-231 cells and increases their CD44 expression. sHA or iHA have no measurable effect on the adhesion, motility or CD44 expression of the ZR-75-1 and MCF-7 breast cancer cells. Our results establish that in high CD44 expressing breast cancer cells HA modulates tumour cell adhesion and motility and also increases the expression of its own receptor, CD44.