Jan Vrba | Czech Technical University in Prague (original) (raw)

Papers by Jan Vrba

2021 15th European Conference on Antennas and Propagation (EuCAP)

The evaluation of non-invasive microwave thermometry using a differential microwave imaging appro... more The evaluation of non-invasive microwave thermometry using a differential microwave imaging approach is investigated in an experimental setup. The setup consists of a monopole microwave tomographic system, a muscle phantom, and a circulation/heating system. The saline solution is used as the heated medium inside the muscle phantom. Based on Born Approximation and regularization by TSVD we reconstructed the distribution of both dielectric parameters, relative permittivity and electrical conductivity inside the investigation area. A promising agreement between measured and reconstructed electrical conductivity was achieved and some specifics for future improvement of microwave thermometry were identified.

The eukaryotic cell is a basic unit of plants, fungi and animals and it is also a likely source o... more The eukaryotic cell is a basic unit of plants, fungi and animals and it is also a likely source of electromagnetic field whose function we would like to examine in the future. Eukaryotic cells contain various organelles and structures. It is expected that the electromagnetic activity originates mainly in cytoskeleton that is a structure that protects and organizes the cell, enables a motion of the cell and is necessary for cell division. This structure is composed of three types of filaments. Microtubules, which are one of them, fulfil all conditions for generation of cellular electromagnetic field. We approximate electrical properties of basic structure of a microtubule (tubulin heterodimer) as elementary electric dipole and then we calculate electromagnetic field around them. In this paper, we present results from calculations of power and electric intensity around two models of microtubule network.

International Journal of Molecular Sciences, Jul 30, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

International Journal of Radiation Biology, Sep 7, 2016

Purpose: Cancer initialization can be explained as a result of parasitic virus energy consumption... more Purpose: Cancer initialization can be explained as a result of parasitic virus energy consumption leading to randomized genome chemical bonding. Materials and methods: Analysis of experimental data on cell-mediated immunity (CMI) containing about 12,000 cases of healthy humans, cancer patients and patients with precancerous cervical lesions disclosed that the specific cancer and the non-specific lactate dehydrogenase-elevating (LDH) virus antigen elicit similar responses. The specific antigen is effective only in cancer type of its origin but the non-specific antigen in all examined cancers. CMI results of CIN patients display both healthy and cancer state. The ribonucleic acid (RNA) of the LDH virus parasitizing on energy reduces the ratio of coherent/random oscillations. Decreased effect of coherent cellular electromagnetic field on bonding electrons in biological macromolecules leads to elevating probability of random genome reactions. Results: Overlapping of wave functions in biological macromolecules depends on energy of the cellular electromagnetic field which supplies energy to bonding electrons for selective chemical bonds. CMI responses of cancer and LDH virus antigens in all examined healthy, precancerous and cancer cases point to energy mechanism in cancer initiation. Conclusions: Dependence of the rate of biochemical reactions on biological electromagnetic field explains yet unknown mechanism of genome mutation.

Journal of Electrical Engineering & Technology, Nov 1, 2016

The main purpose of this article is a complex hyperthermia applicator system design for treatment... more The main purpose of this article is a complex hyperthermia applicator system design for treatment of head and neck region. The applicator system is composed of four waveguides with a stripline horn aperture and circular water bolus. The specific absorption rate (SAR) and temperature distribution from this applicator in various numerical phantom models was investigated. For used targets, the treatment planning based on the optimization process made through the SEMCAD X software is added to show the steering possibilities of SAR and thereby temperature distribution. Using treatment planning software, we proved that the SAR and temperature distribution can be effectively controlled (by amplitude and phase changing) improving the SAR and temperature target coverage approximately by 20 %. For the proposed applicator system analysis and quantitative evaluation of two parameters 25 % iso-SAR and 41°C iso-temperature contours in the treatment area with the respect to sensitive structures in treatment area were defined. To verify our simulation results, the real measurement of reflectivity coefficient as well as the temperature distribution in a homogenous phantom were performed.

Paper deals with the complex permittivity measurement of biological tissues. Ap- plication of a w... more Paper deals with the complex permittivity measurement of biological tissues. Ap- plication of a waveguide probe for this measurement is shown. A non-destructive and non-invasive method based on re∞ection coe-cient measurement attaching the material under test is used. New types of the probes are under investigation | the section of waveguide with H cross-section, the section of waveguide with the rectangular cross-section and with shorted walls, the section of waveguide with inserted dielectric wedge and flnally the section of waveguide fllled with the liquid dielectric. Properties of these prototypes are studied in the frequency range from 300kHz to 3GHz. The method of flnite difierence in time domain is utilized for the numerical modeling and simulation of the re∞ection coe-cient. The condition for the input re∞ection coe-cient of the waveguide probe is the range from (0.7{0.3) in the broad frequency band. Although the waveg- uide is a narrowband microwave component, its modiflcations could have broadband frequency behavior of the re∞ection coe-cient. Results indicate that the most interesting and suitable is the solution with removable dielectric. This liquid dielectric with the low value of permittivity has signiflcant in∞uence on the cut-ofi frequency of waveguide with dominant mode propagation. The knowledge of dielectric parameters of materials is essential for microwave or radio engineers in analysis and synthesis of devices. Relative permittivity, loss factor and conductivity are input parameters for electromagnetic fleld modeling and simulations. Although for many materials these parameters could be found in the tables, very often their experimental determination is necessary. Dielectric properties of biological tissues are determining factors for the dissipation of elec- tromagnetic energy in the human body and therefore they are basic parameters in hyperthermia cancer treatment. Measurement of the dielectric parameters of biological tissues is also a promis- ing method in the medical diagnostics and imaging. Knowledge of the complex permittivity in an area under treatment, i.e., knowledge of the complex permittivity of healthy and tumor tissue, is very important for example in the diagnosing of tumor cell-nests in the human body or in the design of thermo-therapeutic applicators which transform electromagnetic energy into thermal in the pathological tissue (1).

IntechOpen eBooks, Aug 25, 2022

This chapter deals with the description of recent research activities oriented on the perspective... more This chapter deals with the description of recent research activities oriented on the perspective of microwave technologies in medicine and biology. It brings new ideas about the possibilities of using microwaves in thermotherapy—above all toward hyperthermia in cancer treatment. Development of new types of hyperthermia applicators (based, e.g., on technologies such as metamaterials, evanescent modes in waveguides, and other types of transmission structures) will be discussed here. Furthermore, we would like to underline in this chapter perspectives of microwaves in medical diagnostics. It is possible to expect that, e.g., microwave differential tomography, UWB radar, and microwave radiometers (all three can be used both for medical diagnostic and for noninvasive temperature measurement) will soon play an important role in it. Finally, experimental equipment necessary for research on the biological effects of EM fields is presented.

Proceedings of SPIE, Apr 7, 2004

This contribution outlines possibilities of the numerical method for the evaluation of electromag... more This contribution outlines possibilities of the numerical method for the evaluation of electromagnetic field and the temperature distribution in front of the applicator's aperture. This modeling is useful for having basic idea about the distribution of the temperature inside the treated area.

DOAJ (DOAJ: Directory of Open Access Journals), Apr 1, 2008

This paper describes and evaluates a method for determining complex permittivity, and presents re... more This paper describes and evaluates a method for determining complex permittivity, and presents results of permittivity measurement of some substances. Complex permittivity of a phantom of biological muscle tissue, of some industrial chemicals and dielectrics is found. A nondestructive and non-invasive method based on reflection coefficient measurement of an open-ended coaxial line attaching the material under test is used. Two coaxial probes are under investigation. Vector measurement of the reflection coefficient on the interface between probes and measured samples is performed with the aid of network analyzer in the frequency range from 300 kHz to 3 GHz. Numerical modeling (FDTD) is compared with measurement. The results indicate that using the coaxial probe with dimensions of N connector the method is suitable in the frequency range approximately from 30 MHz to 1 GHz and using the probe with dimensions of SMA connector in range approximately from 30 MHz to 3 GHz.

SPIE Proceedings, Apr 7, 2004

Paper deals with new results in the field of intracavitary microwave applicators used for Benign ... more Paper deals with new results in the field of intracavitary microwave applicators used for Benign Prostatic Hyperplasia (BPH) treatment. Costs and risks associated with classical BPH treatment (TURP and open surgery) have promoted the development of minimally invasive methods. Microwave thermotherapy, varying forms of laser treatment, transurethral needle ablation, etc. have all been developed in the 1990s. The underlying principle behind these methods is to coagulate prostatic adenomatous tissue by means of heat. Of all the available minimal invasive treatment modalities, transurethral microwave is one of the most wide spread at present [1]. We have investigated basic types of microwave intracavitary applicators suitable for BPH treatment, i.e., monopole, dipole and a helical coil structures. These applicators are designed to work at 915 MHz. In the conference contribution we would like to discuss it's effective heating depth, based on the comparison of the theoretical and experimental results. Basic mechanisms and parameters influencing (limiting) heating effective depth are described and explained in ref. [2-4]. The basic type of intracavitary applicator is a monopole applicator. The construction of this applicator is very simple, but numerically modelled (calculated by software product SEMCAD) and measured "Specific Absorption Rate" ("SAR") distribution along the applicator is more complicated. During measurements of SAR along the applicator we have found, that typically there is not only a one main "SAR" maximum (first from the right side), but also a second and/or higher order maximas can be created, being produced by outside back wave propagating along the coaxial cable. To eliminate this second maximum and optimise the focusing of "SAR" in predetermined area of biological tissue needs to use the helical coil antenna structure. After coil radius and length optimisation we have obtained very good results of "SAR" distribution. As a novel results of our work we could mention that various microwave applicators for prostate cancer or BPH treatment have been developed and evaluated. Theoretical analysis of effective heating depth of these applicators and its experimental evaluation will be given.

2021 IEEE Conference on Antenna Measurements & Applications (CAMA), 2021

Temperature monitoring during thermal therapies is used to regulate the amount of heat distribute... more Temperature monitoring during thermal therapies is used to regulate the amount of heat distributed to the cancerous tissue and therefore improve the clinical outcome of the oncological treatment. For the development of a hybrid hyperthermia system with non-invasive temperature monitoring by means of ultra-wideband (UWB) imaging, the optimal configuration of sensing antennas and heating applicators has to be investigated. In this paper we present the results of numerical simulations of several possible antenna arrangements, which are then validated by experiments with the radar system. The performance of each channel configuration was analyzed and benefits for the different clinical scenarios were specified.

2008 14th Conference on Microwave Techniques, 2008

Paper deals with the complex permittivity measurement of biological tissues. Application of a wav... more Paper deals with the complex permittivity measurement of biological tissues. Application of a waveguide probe for this measurement is shown. A non-destructive and non-invasive method based on reflection coefficient measurement attaching the material under test is used. New types of the probes are under investigation - the section of waveguide with H cross-section, the section of waveguide with the rectangular cross-section and with shorted walls, the section of waveguide with inserted dielectric wedge and finally the section of waveguide filled by the liquid dielectric. Properties of these prototypes are studied in the frequency range from 300 kHz to 3 GHz. The method of finite difference in time domain is utilized for the numerical modeling and simulation of the reflection coefficient. The condition for the input reflection coefficient of the waveguide probe is the range from (0.7 - 0.3) in the broad frequency band. Although the waveguide is a narrowband microwave component, its modifications could have broadband frequency behavior of the reflection coefficient. Results indicate that the most interesting and suitable is the solution with removable dielectric. This liquid dielectric with the low value of permittivity has significant influence on the cut-off frequency of waveguide with dominant mode propagation.

This article deals with the design and testing of planar microwave two-wireArchimedean spiral app... more This article deals with the design and testing of planar microwave two-wireArchimedean spiral applicator. Applicator is designed to work on the frequency f = 434MHz, aperture has a size of 35mm £ 35mm and its matrix composition consists of the flve applicator of the same type. In this case, aperture has a size of 100mm £ 100mm. Design simulation and the simulations of Speciflc Absorption Rate distribution are created in program CST MICROWAVE STUDIO 2009. Final evaluation of construction solution is established on SIXPORT for S11 coe-cient and evaluation of SAR distribution is evaluated by infrared camera FLIR P25. 1. INTRODUCTION Nowadays the use of microwave thermotherapy is a common part of the clinical hyperthermia oncology treatment. Thus, the paper deals with the prospective type of microwave planar applicator for thermotherapy. The discussed applicator is Archimedean two-wire spiral applicator. We are mainly interested in the shape of radiated power from the aperture and the depth of efiective penetration of the biological tissue. This two main parameters have the crucial impact on the process of hyperthermia oncology treatment. Thus, we want to irradiate the cancerous tissues with the predictable doze of microwave radiation. This is reason why we are running the simulations of this above mentioned microwave thermo therapeutic applicator not only for the impedance matching to the biological tissue, but also for the shape of radiated power from applicator aperture together with the determining the depth of efiective penetration. Numeric veriflcation of SAR distribution is calculated in homogenous plane phantom having electrically the same parameters as the biological tissue.

The Environmentalist, Jul 1, 2007

The effect of long-term exposure to high frequency electromagnetic field (HF EMF) on some somatic... more The effect of long-term exposure to high frequency electromagnetic field (HF EMF) on some somatic and neural characteristics was studied in neurodefective Lurcher mutant (+/Lc) and normal wild type mice (+/+). Both newborn and young adult (3 months) animals derived from two strains (C3H, B6CBA) were exposed to HF EMF (870 MHz) from 1st to 21st day or from 91st to 120th day respectively. In animals of both groups and controls we observed the development of body weight. Moreover, in the HF EMF exposed adult B6CBA animals we studied spatial learning ability, motor functions and the CNS excitability. To investigate specific energy absorption rate (SAR) in experimental animals we have done the basic 3D calculations of the electromagnetic energy distribution in the simplified model of the mouse. The HF EMF exposed animals exhibited mild differences of body weight between them and unexposed controls. The long-term exposure to HF EMF did not significantly influence the ability to learn in the Morris water maze. However, significant lower swimming speed was found in the irradiated +/Lc as well as lower motor activity of +/+ in the open field when compared to controls. No significant differences were found between HF EMF irradiated animals and controls in examination of the CNS excitability and motor functions.

Prague Medical Report, 2012

Physical processes in living cells were not taken into consideration among the essentials of biol... more Physical processes in living cells were not taken into consideration among the essentials of biological activity, regardless of the fact that they establish a state far from thermodynamic equilibrium. In biological system chemical energy is transformed into the work of physical forces for various biological functions. The energy transformation pathway is very likely connected with generation of the endogenous electrodynamic field as suggested by experimentally proved electrodynamic activity of biological systems connected with mitochondrial and microtubule functions. Besides production of ATP and GTP (adenosine and guanosine triphosphate) mitochondria form a proton space charge layer, strong static electric field, and water ordering around them in cytosol – that are necessary conditions for generation of coherent electrodynamic field by microtubules. Electrodynamic forces are of a long-range nature in comparison with bond and cohesive forces. Mitochondrial dysfunction leads to distu...

Principles and Technologies for Electromagnetic Energy Based Therapies, 2022

2017 Progress In Electromagnetics Research Symposium - Spring (PIERS), 2017

The main topic of this contribution is the design and demonstration of combination the hypertherm... more The main topic of this contribution is the design and demonstration of combination the hyperthermia applicator system for head and neck area working on frequency 434 MHz with UWB radar antenna array for differential temperature detection. For our numerical simulations, the simplified homogenous phantom and 3D numerical model of patient were used. For two-dimensional reconstruction of reflected signals the Delay and Sum beamforming algorithm were used. The phantom was locally heated up using the microwave hyperthermia applicator and the temperature distribution was used as an inhomogeneity (through change in relative permittivity and specific conductivity). The results confirm the feasibility and usability of temperature change detection via UWB signal in the head and neck area.