Broadband Dielectric Spectroscopy with a Microwave Ablation Antenna

Microwave ablation is a technique used to treat tumorous tissue. Its clinical use has been greatly expanding in the last few years. Because the design of the ablation antenna and the success of the treatment greatly depend on the accurate knowledge of the dielectric properties of the tissue being treated, it is highly valuable to have a microwave ablation antenna that is also able to perform in-situ dielectric spectroscopy. In this work, an open-ended coaxial slot ablation antenna design operating at 5.8 GHz is adopted from previous work, and its sensing abilities and limitations are investigated in respect of the dimensions of the material under test. Numerical simulations were performed to investigate the functionality of the floating sleeve of the antenna and to find the optimal de-embedding model and calibration option for obtaining accurate dielectric properties of the area of interest. Results show that, as in the case of the open-ended coaxial probe, the accuracy of the measurement greatly depends on the likeness between the calibration standards' dielectric properties and the material under test. Finally, the results of this paper clarify to which extent the antenna can be used to measure dielectric properties and paves the way to future improvements and the introduction of this functionality into microwave thermal ablation treatments

Broadband Dielectric Spectroscopy with a Microwave Ablation Antenna

Microwave ablation is a technique used to treat tumorous tissue. Its clinical use has been greatly expanding in the last few years. Because the design of the ablation antenna and the success of the treatment greatly depend on the accurate knowledge of the dielectric properties of the tissue being treated, it is highly valuable to have a microwave ablation antenna that is also able to perform in-situ dielectric spectroscopy. In this work, an open-ended coaxial slot ablation antenna design operating at 5.8 GHz is adopted from previous work, and its sensing abilities and limitations are investigated in respect of the dimensions of the material under test. Numerical simulations were performed to investigate the functionality of the floating sleeve of the antenna and to find the optimal de-embedding model and calibration option for obtaining accurate dielectric properties of the area of interest. Results show that, as in the case of the open-ended coaxial probe, the accuracy of the measurement greatly depends on the likeness between the calibration standards’ dielectric properties and the material under test. Finally, the results of this paper clarify to which extent the antenna can be used to measure dielectric properties and paves the way to future improvements and the introduction of this functionality into microwave thermal ablation treatments

Dielectric Properties of Healthy Ex-Vivo Ovine Lung Tissue at Microwave Frequencies

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 densit

Dielectric Spectroscopy with the Microwave Ablation Antennas operating at 2.45 and 5.8 GHz

Microwave thermal ablation is a therapeutic technique used to treat tumor in different types of tissue. The technique utilizes a specially designed antenna which increases the tissue temperature causing cellular necrosis. The treatment can be advanced further by utilizing the antenna's potential to perform dielectric spectroscopy of the tissue in-situ. This information can be elaborated to determine the antenna's position in the tissue, monitor the ablation zone evolution and provide additional characterization of malignancies for future scientific studies. This work studied the ability of asymmetric dipole antennas for microwave ablation to perform broadband dielectric spectroscopy. The frequency limitations for measurements were established in respect to the antenna-surrounding material matching and the transversal dimensions of the material in which the antenna is immersed

Characterization of ex-vivo ovine lung tissue in relation to density at microwave frequencies

Lung cancer is the leading cause of cancer deaths worldwide1. Recently, advances in lung navigation technologies have been facilitating progress in minimally-invasive thermal ablative treatments for targeting lung malignancies 2. For the success of microwave thermal ablation, the accurate knowledge of the electromagnetic response of the target, i.e. the tissue’s dielectric properties, is paramount. Nevertheless, lung tissue is the least characterised among the biological tissues, in particular above 100MHz 3. Lung tissue is an heterogenous tissue, with variable air content, resulting in a noticeable variability of the measured properties. In this work, the dielectric properties of ex vivo ovine lung tissue are investigated and correlated with the tissue density, used to estimate the air content

Broadband Dielectric Spectroscopy with a Microwave Ablation Antenna

Microwave ablation is a technique used to treat tumorous tissue. Its clinical use has been greatly expanding in the last few years. Because the design of the ablation antenna and the success of the treatment greatly depend on the accurate knowledge of the dielectric properties of the tissue being treated, it is highly valuable to have a microwave ablation antenna that is also able to perform in-situ dielectric spectroscopy. In this work, an open-ended coaxial slot ablation antenna design operating at 5.8 GHz is adopted from previous work, and its sensing abilities and limitations are investigated in respect of the dimensions of the material under test. Numerical simulations were performed to investigate the functionality of the floating sleeve of the antenna and to find the optimal de-embedding model and calibration option for obtaining accurate dielectric properties of the area of interest. Results show that, as in the case of the open-ended coaxial probe, the accuracy of the measurement greatly depends on the likeness between the calibration standards’ dielectric properties and the material under test. Finally, the results of this paper clarify to which extent the antenna can be used to measure dielectric properties and paves the way to future improvements and the introduction of this functionality into microwave thermal ablation treatments

Wideband Dielectric Characterization of Biological Tissues and Realistic Phantom Preparation at Microwave Frequencies

Oncological hyperthermia is a medical technique whose aim is to heat tumours at 41-43 °C for one hour through the application of an electromagnetic field (EMF). Hyperthermia proved to improve both chemotherapy and radiotherapy. For best hyperthermia performances, the knowledge of the dielectric properties (permittivity and conductivity) of the patient is essential, since these properties represent the response of materials to the applied EMF. This information can be used to optimize the treatment’s results but also to validate the hyperthermia device before the application on the patient. The validation procedure is usually done on phantoms, i.e., mixtures of materials which mimic the dielectric properties of biological tissues. This work presents the realization of a muscle equivalent mixture and the measurement of its dielectric properties with the open-ended probe technique. Results were compared with the dielectric properties of ex-vivo animal muscle samples that were measured with the same procedure

Histology-validated electromagnetic characterization of ex-vivo ovine lung tissue for microwave-based medical applications

Abstract Microwave thermal ablation is an established therapeutic technique for treating malignant tissue in various organs. Its success greatly depends on the knowledge of dielectric properties of the targeted tissue and on how they change during the treatment. Innovation in lung navigation has recently increased the clinical interest in the transbronchial microwave ablation treatment of lung cancer. However, lung tissue is not largely characterized, thus its dielectric properties investigation prior and post ablation is key. In this work, dielectric properties of ex-vivo ovine lung parenchyma untreated and ablated at 2.45 GHz were recorded in the 0.5–8 GHz frequency range. The measured dielectric properties were fitted to 2-pole Cole–Cole relaxation model and the obtained model parameters were compared. Based on observed changes in the model parameters, the physical changes of the tissue post-ablation were discussed and validated through histology analysis. Additionally, to investigate the link of achieved results with the rate of heating, another two sets of samples, originating from both ovine and porcine tissues, were heated with a microwave oven for different times and at different powers. Dielectric properties were measured in the same frequency range. It was found that lung tissue experiences a different behavior according to heating rates: its dielectric properties increase post-ablation while a decrease is found for low rates of heating. It is hypothesized, and validated by histology, that during ablation, although the tissue is losing water, the air cavities deform, lowering air content and increasing the resulting tissue properties