Thermo-controlled device for inducing deep coagulation in the liver with the Nd:YAG laser

Abstract

Background and Objective To increase the effectiveness of laser‐induced interstitial thermotherapy (LITT), a new thermo‐controlled application system for minimal invasive intervention was designed. Our system consists of a laser applicator of 2.5 mm in diameter, insertion equipment, and a Nd:YAG‐laser source. Study Design/Materials and Methods A cylindrical light emitting fiber (1–6 cm in length) was placed in the center of the applicator. The surrounding tissue was irradiated through a Duran® window at the distal end of the applicator. The power of the laser source was controlled dynamically by thermosensors in a water‐cooling system of the laser applicator. The temperature at the surface of the Duran® window was kept constant at ∼60°C, without charring the surrounding tissue. Results/Conclusion We obtained homogeneous coagulation zones. In in vitro experiments with pig livers, we reached ellipsoid coagulation volumes of 3 and 5 cm in diameter within 10 minutes, corresponding to a volume of ∼25 cm3. Lasers Surg. Med. 20:149–156, 1997. © 1997 Wiley‐Liss, Inc.

Microwave Tissue Ablation: Biophysics, Technology, and Applications

“…Rapid impedance elevation during RF ablation near 100 °C is also known to inhibit electrical current flow, effectively halting further application of RF energy unless the tissue is cooled and allowed to rehydrate, or artificially hydrated using ionic fluid infusion 22–24. A similar problem exists with laser and ultrasound energies, where high-temperature heating can inhibit further energy application 25, 26. By comparison, while dielectric properties can change substantially during treatment, microwave propagation is not hindered by these changes 14.…”

Laserinduzierte Thermotherapie Technische Voraussetzungen zur Behandlung maligner Lebertumoren

“…Eine weitere Steigerung der Coagulationseffizienz Applikatoren ist durch eine Erhöhung der maximalen thermischen Belastbarkeit mittels Kühlung des Applikatorschaftes erzielbar [13,16]. Von der eigenen Arbeitsgruppe wurde inzwischen ein gekühltes Applikationssystem entwickelt, im Vergleich mit ungekühlten Diffuser-Tip-Applikatoren sind deutlich gröûere Coagulationsvolumina von bis zu 25 cm 3 induzierbar [16].…”

“…Von der eigenen Arbeitsgruppe wurde inzwischen ein gekühltes Applikationssystem entwickelt, im Vergleich mit ungekühlten Diffuser-Tip-Applikatoren sind deutlich gröûere Coagulationsvolumina von bis zu 25 cm 3 induzierbar [16]. Orth et al entwickelten einen gekühlten Streuapplikator mit integrierter Temperaturmessung mittels eines distalen Temperatursensors, der eine automatische Anpassung der Laserleistung an die Kontakttemperatur ermöglicht [13]. Ein weiterer Nachteil der gekühlten Applikatoren ist in den deutlich höheren Kosten zu sehen.…”

Feedback control of liver thermotherapy using optical spectroscopy

“…This approach has been previously investigated using thermocouples [13,14] and intraoperative MRI [15][16][17]. Currently, some RFA systems use embedded thermocouples in the electrode arrays to provide continuous temperature readings; these local temperatures can be used in a feedback control mode to modulate ablation power in order to achieve and maintain a certain target temperature.…”