Comparison of coaxial open-ended probe based dielectric measurements on ex-vivo thermally ablated liver tissue (original) (raw)
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Physics in Medicine and Biology, 2007
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.
IEEE Transactions on Biomedical Engineering, 2018
The released energy during radio frequency thermal ablation (RFTA) therapy changes the dielectric properties of biological tissues. Understanding changes of dielectric properties of biological tissues during heating is fundamental to suitably model the medical procedure. The aim of this work is to obtain the thermal dependences of conductivity and permittivity of ex-vivo porcine liver tissue at six frequencies from 5 to 500 kHz, during heating from 37 °C to 100 °C at three heating rates of approximately 0.1, 3 and 10 °C/min. Methods: Two experimental setups using different heating sources and a four-needle electrode connected to an Impedance Analyzer were developed to evaluate the thermal dependencies. Results: The results at a body temperature of 37 °C show a good agreement with the data reported in the literature. The conductivity initially shows an increase followed by a decrease, whereas the permittivity increases before a subsequent sharp decrease. Above 60 °C different trends are observed for the three heating rates studied. Conclusion: The electric conductivity and permittivity show a similar behavior at all evaluated frequencies and heating rates. The observed abrupt change of the slope near 45 °C at slow heating rate may be used to identify the region of reversible changes in the tissue. Significance: These results confirm the connection between tissue dielectric properties, working frequency and exposure time with thermal damage during heating.
Physics in Medicine and Biology, 1996
Three experimental techniques based on automatic swept-frequency network and impedance analysers were used to measure the dielectric properties of tissue in the frequency range 10 Hz to 20 GHz. The technique used in conjunction with the impedance analyser is described. Results are given for a number of human and animal tissues, at body temperature, across the frequency range, demonstrating that good agreement was achieved between measurements using the three pieces of equipment. Moreover, the measured values fall well within the body of corresponding literature data.
—The development of microwave tumor ablation devices depends largely on numerical simulations of antenna characteristics and transient electromagnetic heating. However, without an adequate tissue model simulation predictions can vary widely from experimental results. In this study, tissue dielectric properties are measured to capture changes induced by temperature, cellular makeup and water content during thermal ablation. Measurements made using this technique agree closely with previous measurements for temperatures up to 50 °C, but both relative permittivity and conductivity decrease by as much as 50 percent when temperatures approach 100 °C.
Dielectric properties of animal tissues in vivo at frequencies 10 MHz – 1 GHz
Bioelectromagnetics, 1981
An open-ended coaxial line sensor in conjunction with an automatic network analyzer was used to measure in vivo the permittivity of several feline tissues (skeletal and smooth muscle, liver, kidney, spleen, and braingray and white matter) at frequencies between 10 MHz and 1 GHz. The estimated uncertainties of measurement were between 1.5% and 5%. The data are in general agreement with previously obtained data in vitro and in vivo. Significant differences in the properties of different types of the same tissue (eg, skeletal and smooth muscle) were observed. Many tissues were found to be non-homogeneous in its permittivity.
Study of Dielectric Properties of Biological Tissues in the Microwave Frequency Range
2009
The complex dielectric constants at room temperature of various goat tissues (liver, muscle, kidney, heart and brain) and corn syrup were measured in the frequency range 1 to 10 GHz with the help of a HP Network Analyzer N5230A. Open ended coaxial cable method was employed for the measurement. The system imperfections are completely avoided by calibrating the system with four known materials and their reflection coefficients were used in the calculation along with the reflection coefficient of the sample. The relaxation frequency in the δ region, spread of relaxation, volume fraction of protein present in tissues are calculated from the measured dielectric data. The dielectric constant of corn syrup samples suggests the feasibility of using corn syrup as a tissue equivalent for microwave imaging applications. Introduction and Scope Electrical properties of biological materials and their interaction with electromagnetic waves have attracted the attention of researchers working in the...
Microwave Estimation of Dielectric Properties of Biological Tissue Under Thermal Modification
Archiv Euromedica
The aim of this study was to estimate changes of tissue dielectric parameters under the action of high temperature. We fixed the shifts of dielectric properties of biological tissue samples, associated with short-time influence of high temperature (600C, 5 min.) in vitro. The dielectric properties of tissues (permittivity - ε and conductivity - σ) were determined using original software and hardware complex for near-field resonant microwave sensing developed at the Institute of Applied Physics of the RAS. The study of these parameters was performed at a depth of 5 mm. It was found that short processing of a biological sample in moderate hyperthermia (600C) leads to significant change of dielectric characteristics of the tissue. This is manifested in a significant decrease in the dielectric permittivity (in 2.48 times for an intact specimen) and conductivity (on 25.3%) of the studied biological sample, due to its dehydration. It was shown that used regimen of heating decreases the pe...
Dielectric Properties of Healthy Ex-Vivo Ovine Lung Tissue at Microwave Frequencies
IEEE Transactions on Dielectrics and Electrical Insulation
Knowledge of dielectric properties of lung tissue is fundamental for the improvement of lung disease diagnostics and therapeutic solutions (e.g. microwave imaging and microwave thermal ablation treatment). Although lung disease rates are increasing, lung tissue remains one of the least characterized tissues due to its heterogeneity, variability in air content, and handling difficulties. In this work, dielectric properties of ex-vivo ovine lung tissue samples were measured in the frequency range 500 MHz-8 GHz, together with measurements of sample density (air content). Different Cole-Cole models were applied to the measured dielectric properties values. The best fitting model was chosen, and results were compared with available literature. Furthermore, the dielectric property measurements were correlated with the air content of the samples. Updated Cole-Cole models for lung tissue of different density is provided in the 500 MHz-8 GHz range. The existence of air content threshold in lung is shown. Below this limit, the properties begin to change drastically with the change in density. Index Terms-Cole-Cole model fitting, dielectric spectroscopy, lung tissue air content, lung tissue dielectric properties, open-ended coaxial probe I. INTRODUCTION NOWLEDGE of tissue dielectric properties is paramount in various electromagnetic-based medical applications such as diagnostics, therapy, dosimetry, and monitoring. A diagnostic and monitoring technique relying on dielectric properties knowledge is Microwave Imaging (MWI) [1]. MWI determines the position of healthy and malignant tissue based on contrast in dielectric properties. Examples of its use from the literature are in the liver [2], and lately, in lung tissue [3]. A therapeutic technique that benefits from an accurate knowledge of the dielectric properties is microwave thermal ablation (MWA) [2], [4], [5]. While tissues such as liver [5]-[7], heart [6], muscle [5], [6], [8], and breast tissue [9] are well characterized, lung tissue remains insufficiently studied in the microwave range due to handling difficulties and tissue heterogeneity [6]. Nevertheless, the number of lung diseases diagnosed yearly is continuously rising, the incidence of lung cancer is second This research was funded by Government of Ireland, Disruptive Technology Innovation Fund (DTIF), grant number DT2020189. K. Vidjak and M. Cavagnaro are with the
2018
RESUMEN A comparative numerical study of three probe types with the same radial dimensions, three probe models, and five reference materials is presented for six biological tissues: liver, muscle, kidney, heart, blood and fat. The Probe-Model-Reference (PMR) combinations that lead to the most accurate results of the permittivity at frequencies from 300 MHz to 3 GHz are investigated for a coaxial probe without flange, a coaxial probe with flange, and a coaxial probe open into a propagation circular wave guide. The probe models considered are capacitive model, antenna model, and virtual line model. The reference materials are distilled water, 0.02 M NaCl(aq) solution, ethanol, methanol and 0.5 M NaCl(aq) solution. The results corroborates that when measuring the RF permittivity of biological materials using an open-ended coaxial line the proper selection of the probe type, probe model and reference material is crucial if good accuracy of measurements is expected. The presented methodo...
In vivo and in vitro dielectric properties of animal tissues at radio frequencies
Bioelectromagnetics, 1982
An open-ended coaxial tine and an improved measurement method employing a computer controlled network analyzer were used to measure the permittivity of cat tissues. Muscle, spleen, kidney cortex, liver,and brain cortex were measured in vivo and in vitro at frequencies between 100 MHz and 8 GHz. The differences between the permittivities of these cat tissues, in the aforementioned range of frequencies, when measured in vivo and a few (up to four) hours after death, were found to be within the experimental uncertainty.