Piotr Gas

Specifying the ferrofluid parameters important from the viewpoint of magnetic fluid hyperthermia

The article presents the experimental study of magnetic fluid hyperthermia (MFH) utilizing magnetite nanoparticles with diameter of 15.2 nm. Temperature measurements of the ferrofluid samples were carried out in real measurement system using parallel resonance phenomenon. Based on the obtained temperature curves the basic heating parameters of ferrofluid, namely the Specific Absorption Rate (SAR) and power losses in tested nanoparticles have been specified. The authors systematize the current knowledge of these quantities and additionally propose two models that simplify their determination with given errors, omitting the mass and volume concentrations of the individual components of magnetic fluid.

Transient Analysis of Interstitial Microwave Hyperthermia Using Multi-slot Coaxial Antenna

This paper outlines the impact of the number of air gaps appearing in the microwave antenna structure on the transient temperature distribution in the human tissue. From the mathematical point of view this problem can be described by coupling the wave equation in sinusoidal steady-state and the bioheat transfer equation in transient form with the adequate boundary-initial conditions. Moreover, the Cole–Cole model has been used to evaluate the complex relative permittivity of the human tissues for the antenna operating frequency of 2.45 GHz. At the stage of numerical realization the finite element method has been applied. The computational results in case of the 2D analysis of singe-, double- and triple-slot antennas are presented and compared to each other for several tissues typically treated during interstitial microwave hyperthermia.

Determination of the optimal multi-slot coaxial antenna sizes based on the microwave antenna reflection coefficient characteristics

This paper describes a method of determination of the optimal sizes and locations of cylindrical air gaps inside the multi-slot coaxial antenna operating at 2.45 GHz. The dimensions of the microwave antenna with a 50-ohm coaxial feed were revised with regard to antenna reflection coefficient distributions. It should be emphasized that there are some differences between the operating frequencies of such antennas described in the literature and the resonant frequencies obtained from the antenna characteristics. It may significantly affect the interstitial hyperthermia treatment. It is also possible to resize the antenna slots to minimalize the S11-parameter value and obtain the best antenna impedance matching inside various tissues commonly treated in this method. The numerical implementation of such multi-physical problem is based on the finite element method.

The S 11 -parameter Analysis of Multi-slot Coaxial Antenna with Periodic Slots

The motivation behind this study is specifying the proper arrangement of periodic air slots within the multi-slot coaxial antenna with 50-Ω feeding load operating at 2.45 GHz to provide the conformal microwave thermotherapy. The desired temperature profile of the liver tissue was numerically evaluated for coupled electromagnetic and thermal problems by the finite element method. Considering the growing number of radiating apertures within the thin microwave needle applicator requires some unique optimization approach based on the S 11-parameter characteristics to guarantee the best antenna–tissue impedance matching. Moreover, the proposed multi-step iterative numerical procedure allows effective modelling of optimal placement of the periodic slots of microwave antenna, required limit levels of the antenna power input and thus conformal cancer treatment for both interstitial microwave hyperthermia and thermal ablation.

SAR calculations for titanium bar-implant subjected to microwave radiation

The paper describes the assessment of exposure of a six-year-old male patient with a titanium bar implanted after Nuss procedure to microwave radiation with frequency of 2.45 GHz. The local SAR concentrations inside the boys trunk for two variants of plane wave polarizations with regard to the titanium implant have been considered. It was demonstrated that an analyzed concave bar-implant poses no danger during occupational and environmental exposures according to current safety standards.

Mutual Forces Acting on Chains of Particles

This paper describes a method to determine mutual forces acting between dielectric particles, which form chains. The Maxwell stress tensor method together with finite element method are used. It is shown that particles placed in inhomogeneous field, because of dielectrophoretic forces acting between them, have a tendency to collect one by one giving in effect even long particles chains. In this article, Maxwell stress tensors are integrated over particle surfaces to give total mutual forces interacting between molecules.

Magnetophoretic placement of ferromagnetic nanoparticles in RF hyperthermia

This article presents a method of permanently placing ferromagnetic particles in the tumor region for the duration of the treatment. It is based on the phenomenon of magnetophoresis, that is, the influence of a magnetic field with a strongly variable gradient on magnetically induced magnetic moment of particle. The presented approach has a great importance in particle separation industry as well as in nanoparticle tumor targeting.

Cooling effects inside water-cooled inductors for magnetic fluid hyperthermia

The paper lists several well-known formulas for on-axis magnetic field inside ideal solenoid and compares them with the values obtained from the computer simulation of the actual water-cooled coil for magnetic fluid hyperthermia (MFH) purpose. Performed analysis of coupled electro-thermal problem using finite element method (FEM) may led to the estimation of impact of heat losses due to water cooling on temperature within a region of interest (ROI) for some important model parameters. It is shown that cold water circulating inside the copper windings cause significant cooling of such inductors. What is important, it enables convenient conditions for ferrofluid testing and reliable operation of temperature sensors placed inside helical coils.

Comparative analysis between the 2D and 3D models of interstitial microwave hyperthermia

The aim of this study is the comparison of the 2D and 3D finite element time-dependent analysis for interstitial microwave hyperthermia treatment. The described method is based on microwave heating of pathologic human tissue using a thin coaxial-slot antenna placed invasively in the diseased tissue. The shown problem relies on the solving of coupled electromagnetic and thermal fields under the assumption of an axial symmetrical model. The wave equation in a sinusoidal steady state and the bioheat equation under a transient state condition are considered. The numerical calculations for the 2D and 3D models give consistent results with an acceptable level of relative error. Increasing the finite element mesh density for the refined 2D* model leads to a more accurate evaluation of the tissue temperature while reducing computation time.

Numerical analysis on cathodic protection of underground structures

The presented paper describes the principles of cathodic protection (CP) of underground tanks using the sacrificial anode as well as method of calculation of the potential, current density and polarization distribution on all sides metallic tanks buried underground. Differential equations with boundary conditions are developed and next solved by FEM in 2D and 3D cases. The main goal of this publication is the computation of such distribution of the external protecting electrodes where protected structure will not corrode and next the calculations in 2D and 3D were compared. The article shows that it is sufficient to use 2D analysis for which the speed of equations solution is significantly larger than in 3D space.