Iordana Astefanoaei

Controlling temperature in magnetic hyperthermia with low Curie temperature particles

Hyperthermia induced by the heating of magnetic particles (MPs) in alternating magnetic field receives a considerable attention in cancer therapy. An interesting development in the studies dedicated to magnetically based hyperthermia is the possibility to control the temperature using MPs with selective magnetic absorption properties. This paper analyzes the temperature field determined by the heating of MPs having low Curie temperature (a FeCrNbB particulate system) injected within a malignant tissue, subjected to an ac magnetic field. The temperature evolution within healthy and tumor tissues was analyzed by finite element method simulations in a thermo-fluid model. The cooling effect produced by blood flowing in blood vessels was considered. This effect is intensified at the increase of blood velocity. The FeCrNbB particles, having the Curie temperature close to the therapeutic range, transfer the heat more homogeneous in the tumor keeping the temperature within the therapeutic range in whole tumor vol...

Internal stress distribution in DC joule-heated amorphous glass-covered microwires

As known, the magnetic properties of AGCMs are determined by the radial, azimuthal and axial internal stresses induced during both the preparation process and the suitable thermal treatments of these microwires. In this paper we have proposed a theoretical model in order to determine the total internal stresses induced during the dc joule-heating thermal treatment (heating?crystallization?cooling). In this view (i) we have started from the internal stress values obtained in the preparation process, (ii) we have considered the supplementary axial tensile stresses due to the mechanical drawing of the microwire during the preparation process and (iii) we have taken into account the difference between the thermal expansion coefficients of metal and glass. We have found that (i) the maximum value of the axial stresses obtained after the thermal treatment is bigger than that obtained in the preparation process, the difference being about 450?MPa, (ii) the maximum values for the azimuthal and radial stresses decrease by and ?MPa respectively, (iii) the dimensions of the cylindrical inner core increase significantly (by ), which involves an increase of the degree of magnetic order in the AGCMs and consequently leads to the appearance of a large Barkhausen effect (LBE) in low axially applied magnetic fields and (iv) the reduced remanence increases from 0.90 to 0.95.

Thermofluid Analysis in Magnetic Hyperthermia Using Low Curie Temperature Particles

Magnetic hyperthermia uses the targeted therapeutic heat from magnetic particles (MPs) in an alternating magnetic field to kill cancer cells. MPs with low Curie temperature (Tc) (in the range 42°C-45°C), high magnetization, and magnetic permeability/susceptibility are good candidates for their use in hyperthermia therapy. This paper analyzes the hyperthermic effects determined by the MPs with low Tc within a tumoral configuration from healthy tissue when an alternating magnetic field is applied. The temperature field was determined as a solution of the Pennes bioheat transfer equation. The spatial distribution of the particles after their injection within the tissues was computed by solving the convection-diffusion equation in porous tissues. Results show that the MP injection rate significantly influences the spatial distribution of the particles and the temperature field of the tumor. Higher values of the ferrofluid flow rate push more particles to the tumor center, thus also elevate its central temperature. The temperature field becomes uniform in a percentage of 90% of tumor volume if a blood vessel is localized at the tumor center.

The temperature dependence of hysteretic processes in Co nanowires arrays

In this paper, the temperature dependence of the hysteretic processes of Co nanowires, squarelly ordered in an array prepared by electrodeposition in nanopores of alumina membranes was analyzed. Both the magnetostatic interactions induced in the nanowires arrays and the thermal stresses radial, azimuthal and axial stresses, which appear during the cooling of the system nanowire and alumina template from room temperature to 3 K was evaluated. The analysis of thermal induced stresses provides useful informations concerning the magnetic anisotropy in the Co nanowires. The temperature dependence of the remanent magnetization and coercitive field as an effect of the induced thermal stresses and magnetostatic interactions between nanowires was studied.

A thermo-fluid analysis in magnetic hyperthermia

In the last years, hyperthermia induced by the heating of magnetic nanoparticles (MNPs) in an alternating magnetic field received considerable attention in cancer therapy. The thermal effects could be automatically controlled by using MNPs with selective magnetic absorption properties. In this paper, we analyze the temperature field determined by the heating of MNPs, injected in a malignant tissue, subjected to an alternating magnetic field. The main parameters which have a strong influence on temperature field are analyzed. The temperature evolution within healthy and tumor tissues are analyzed by finite element method (FEM) simulations in a thermo-fluid model. The cooling effect produced by blood flow in blood vessels from the tumor is considered. A thermal analysis is conducted under different distributions of MNP injection sites. The interdependence between the optimum dose of the nanoparticles and various types of tumors is investigated in order to understand their thermal effect on hyperthermia therapy. The control of the temperature field in the tumor and healthy tissues is an important step in the healing treatment.

Induced Thermal Stresses in Core Shell Magnetic Particles

In this paper, the induced thermal stresses that appear during the cooling process from the room temperature to a lower temperature for core shell magnetic particles are analyzed. Using a finite element method for solving the Fourier heat transport equation, the thermal stresses in the system were calculated taking into account of the temperature dependence of thermal conductivity, heat capacity and different thermal expansion coefficients of the two materials (iron core + alumina shell) in contact. The thermal stresses depend on the particles radius and the thickness of the alumina shell, having negative values due to the thermal contraction. It was estimated the influence of shell thickness on thermal stresses and on the speed of reaching the mechanical and thermal equilibrium state.

Thermal performance of Fe-Cr-Nb-B systems in magnetic hyperthermia

In magnetic hyperthermia, the temperature control within the malignant tissues is an important step to increase the efficiency of the therapy. A temperature analysis is a good method to improve the heating process of the magnetic particles injected within tissues. This paper analyzes the thermal effects induced within malignant tissues by the magnetic systems like: magnetite and Fe-Cr-Nb-B when an external time-dependent magnetic field is applied. The heat generation by Neel and Brown relaxations was modeled using the thermal and magnetic properties of the Fe-Cr-Nb-B particles experimentally determined. A lognormal particle size distribution was considered for these magnetic systems with dimensions from 5 nm to 30 nm. After their injection at the center of the tumor, according to the solution of the transient convection-diffusion equation in a porous medium, the mass concentration of the particles within ferrofluid has a spatial and temporal distribution. The ferrofluid injection process was modeled using...

Magnetic hyperthermia with Fe - Cr- Nb - B magnetic particles

The temperature field developed by the magnetic nanoparticles injected directly within malignant tissues provides precious information about the main parameters which influence their heating mechanisms. This paper analyses the temperature field induced within a tumoral tissue by the Fe - Cr - Nb - B and magnetite systems, when an external time - dependent magnetic field is applied. An analytical temperature model which predicts the temperature in a tumoral tissue was developed. The particles with a lognormal size distribution were considered. The heat generation by Neel and Brown relaxations was modeled using the thermal and magnetic properties of the Fe - Cr - Nb - B particles experimentally determined. Fe - Cr - Nb - B magnetic systems have a particular behavior with the frequency and amplitude of the AC magnetic field. The temperature field can be controlled by tuning of the magnetic field parameters. As a result of their magnetic and thermal properties, these systems can be used for the magnetic hyper...

Monitoring the thermal effects in the magnetic hyperthermia

Magnetic hyperthermia is a clinical therapy which uses the heat given by the magnetic nanoparticles (MNPs) in alternating magnetic fields for the treatment of various cancers. The control of temperature within the tumor and healthy tissues is an important step for the success of this therapy. This paper analyzes the temperature field determined by the heating of FeCrNbB systems injected within a tumor subjected to an alternating magnetic field. The temperature inside as well as outside the tumor was computed by finite element method (FEM) in a thermo-fluid model. The cooling effect produced by blood flowing in a blood vessel (BV) inside the tumor was take into account. The frequency and amplitude of magnetic field, MNPs concentration are optimized to obtain the temperature therapeutic range: 41 - 45 Celsius degrees within tumors with different sizes. The heat propagation is focused in tumor volume due to MNPs magnetic and thermal characteristics.

Dissipation and Thermal Time Constants in Graphite of an Ultra-Small Bead Thermistor

The thermistors are indispensable devices in experimental arrangements for electrical calibration of graphite calorimeters. The present experiments determine the two basic thermal constants in graphite – the thermal time constant, \( \tau_{g} \) and dissipation constant, \( \delta_{g} \) – of commercially-available VECO ultra-small bead thermistors; these constants are essential parameters in thermal modeling of graphite calorimeters. For the above-mentioned kind of thermistors, the dissipation constant in graphite is found to be approximately ten times larger than that in still air, whereas the thermal time constant in graphite is approximately one hundred times smaller than that corresponding to a thermistor placed in still air.