M. A. Golombeck, O. Dössel, and J. Raiser. Improvement of patient return electrodes in electrosurgery by experimental investigations and numerical field calculations. In Med Biol Eng Comput, vol. 41(5) , pp. 519-528, 2003
Numerical field calculations and experimental investigations were performed to examine the heating of the surface of human skin during the application of a new electrode design for the patient return electrode. The new electrode is characterised by an equipotential ring around the central electrode pads. A multi-layer thigh model was used, to which the patient return electrode and the active electrode were connected. The simulation geometry and the dielectric tissue parameters were set according to the frequency of the current. The temperature rise at the skin surface due to the flow of current was evaluated using a two-step numerical solving procedure. The results were compared with experimental thermographical measurements that yielded a mean value of maximum temperature increase of 3.4 degrees C and a maximum of 4.5 degrees C in one test case. The calculated heating patterns agreed closely with the experimental results. However, the calculated mean value in ten different numerical models of the maximum temperature increase of 12.5 K (using a thermodynamic solver) exceeded the experimental value owing to neglect of heat transport by blood flow and also because of the injection of a higher test current, as in the clinical tests. The implementation of a simple worst-case formula that could significantly simplify the numerical process led to a substantial overestimation of the mean value of the maximum skin temperature of 22.4 K and showed only restricted applicability. The application of numerical methods confirmed the experimental assertions and led to a general understanding of the observed heating effects and hotspots. Furthermore, it was possible to demonstrate the beneficial effects of the new electrode design with an equipotential ring. These include a balanced heating pattern and the absence of hotspots.
In the last few years, radioactive stents has been proved to inhibit neointima formation. This paper describes the actual status of producing such radioactive stents. After a short discussion of the different radioisotopes suitable for radioactive stents, potential production methods are discussed. The ion beam implantation of P-32 applied at the Karlsruhe Research Centre shall be described in more detail.
Conference Contributions (21)
M. A. Golombeck, and O. Dössel. MR-tomography on patients with heart pacemakers-a numerical study. In Conference Proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, vol. 2, pp. 1076-1079, 2004
Patients having a heart pacemaker are not allowed to go to MR tomography (MRT). One of the most dangerous effects is the heating of the tissue around the electrode caused by the coupling to the RF field of the MR system. Experiments have been carried out using tanks filled with saline water and large heating has sometimes been observed. Other experiments e.g. with electrodes in the brain did not show any heating at all. In this work numerical studies have been carried out to understand the different results. In conclusion it is suggested that MRT could be possible if the "normal" geometry of the wires of a heart pacemaker is ensured and an open MR system is used.
M. A. Golombeck, and O. Dössel. Magnetic resonance imaging and implanted electrodes: Deduction of rules for reducing hazards for patients by the use of numerical methods. In Biomedizinische Technik, vol. 48-1, pp. 366-367, 2003
M. A. Golombeck, J. Thiele, and O. Dössel. Magnetic resonance imaging with implanted neurostimulators: numerical calculation of the induced heating. In Biomedizinische Technik, vol. 47-1, pp. 660-663, 2002
Magnetic resonance imaging (MRI) is still contraindicated in patients with implanted active medical devices, as the applied radiofrequency (RF) fields can lead to significant heating of the implants and the electrodes. A head model with an implanted deep brain stimulation electrode (DBS) was exposed to a continuous RF-field similar to the excitational field used in MRI at a frequency of 64 MHz. In this study a two-step procedure for the accurate estimation of electrode-heating during MRI is presented. First the energy loss was calculated in the frequency domain during an applied RF-pulse. Then a thermodynamic algorithm taking heat transfer mechanisms into account was used. The applied method showed to be numerically stable and gave more accurate results than first calculated using a simple worst-case approximation.
M. A. Golombeck, C. H. Riedel, and O. Dössel. Calculation of the Dielectric Properties of Biological Tissue using simple Models of Cell Patches. In Biomedizinische Technik, vol. 47-1, pp. 253-256, 2002
M. A. Golombeck, M. Tabbert, and O. Dössel. Numerische Berechnung elektromagnetischer Felder in einem Oberkörperphantom mit Elektroden bei der Magnetresonanztomographie. In Biomedizinische Technik, vol. 46-1, pp. 464-465, 2001
M. A. Golombeck, and O. Dössel. Simulation der Auswirkung medizinischer Therapie- und Diagnosemethoden auf den menschlichen Körper unter der besonderen Berücksichtigung von Implantaten. In Biomedizinische Technik, vol. 45-1, 2000
C. H. Riedel, M. A. Golombeck, and O. Dössel. Simulation study for the non-contact measurement of the impedance of biological tissue using an axial gradiometer. In Proc. IEEE EMBS and BMES, pp. 1748-1749, 2002
The paper presents a simulation of the transient temperature distribution in the human body caused by induced eddy currents during magnetic resonance imaging (MRI). In a first simulation the validity of the used heat conduction equation was proven using a simple example of a cool-down-process of a sphere. Thereafter the heating of a phantom model with an implanted electrode placed in a MRI-System (active body coil) was examined. The resulting increase in temperature was compared with existing measurements. Finally the implications of the heating of the tissue are discussed based on the observed experimental and numerical results.
M. A. Golombeck. Feldtheoretische Studien zur Patientensicherheit bei der Magnetresonanztomographie und der Elektrochirugie. Universität Karlsruhe (TH), Institut für Biomedizinische Technik. Dissertation. 2003