Finite Element Analysis of Hepatic Radiofrequency Ablation Probes using Temperature-Dependent Electrical Conductivity

BACKGROUND: Few finite element models (FEM) have been developed to describe the electric field, specific absorption rate (SAR), and the temperature distribution surrounding hepatic radiofrequency ablation probes. To date, a coupled finite element model that accounts for the temperature-dependent electrical conductivity changes has not been developed for ablation type devices. While it is widely acknowledged that accounting for temperature dependent phenomena may affect the outcome of these models, the effect has not been assessed. METHODS: The results of four finite element models are compared: constant electrical conductivity without tissue perfusion, temperature-dependent conductivity without tissue perfusion, constant electrical conductivity with tissue perfusion, and temperature-dependent conductivity with tissue perfusion. RESULTS: The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures. These errors appear to be closely related to the temperature at which the ablation device operates and not to the amount of power applied by the device or the state of tissue perfusion. CONCLUSION: Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100°C

Laserforschung. Grundlagenuntersuchungen zur Wirkung der kombinierten Anwendung von NIR-Laserstrahlung und Hochfrequenzstrom Abschlussbericht

fState of research: Biological tissue is cut and coagulated by NIR-lasers and monopolar RF (radio frequency)-current. Bipolar RF-cutters are occasionally available. Bipolar interstitial coagulation has not been performed yet. The possibilities of the combination of both types of energy has not been investigated yet too. Reason for / aim of investigation: It has to be investigated if an improvement of surgical procedures (cutting, coagulation, interstitial coagulation) is possible by the combination of laser radiation and RF-current. Method: Construction of bipolar RF-cutting applicators and bip. RF-ITT (interstitial thermotherapy) probes (bringgn the RF-ITT to the same level of development as the LITT). Construction of combined instruments (cutting with RF, coagulating with the laser). In-vitro-investigation of the effect on biological tissue. Development of a computer model for the simulation of the interstitial application of laser radiation and RF current. Results: The bipolar RF-cutter and the RFITT probe respectivley, have proven to be a powerful alternative to the corresponding laser techniques (bare fiber / focusing hand piece, LITT). The combination of laser radiation and RF current does only make sense in those cases when both techniques are assigned different tasks (e.g. RF for cutting and laser for coagulation in case of bleedings). If both types of energy are used for the same purpose (e.g. ITT) no improvement can be achieved in comparison to a single application. Conclusion / possible applications: Bipolar RFITT is a new kind of therapy with versatile possibilities of application in the field of ENT (concha hyperplasia), urology (benign prostate hyperplasia) and interventional radiology / surgery (liver metastases). The constructive (and financial) effort building up combined instruments is not justified in most of the cases. Especially for use in ITT an applicator build up solely in bipolar RF technique is a skillful and good value instrument. (orig.)SIGLEAvailable from TIB Hannover: F99B779+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Grundlagenuntersuchungen zur Ultraschall- und Laserlichtuebertragung ueber Lichtwellenleiter (LUST)

SIGLEAvailable from TIB Hannover: F97B1205+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman