Effects of magnetic thermoablation in muscle tissue using iron oxide particles: an in vitro study.

RATIONALE AND OBJECTIVES To study the effects of magnetic thermoablation in muscle tissue from cow to assess interrelations that might be relevant for a minimally invasive therapy system in the long term. METHODS Magnetite particles (50-180 mg) were placed in muscle tissue. Temperature elevations as a function of time and distance from the center of the magnetite deposition area were measured during the exposure (up to 304 seconds) to an alternating magnetic field (frequency 400 kHz, amplitude 6.5 kA/m) generated by a circular coil (diameter 90 mm). Measured curves were reproduced by numerical calculations. Tissue alterations, macroscopically visible as light-brown discoloration, were recorded by volume estimations and histopathologic studies. RESULTS Significant temperature elevations (up to 87 degrees C) were reported within a distance of less than 15 mm from the magnetite deposition area. High initial heating rates were observed during the first 150 seconds of heating. The reproduction of the measured curves by numerical calculations was good (SD = 0.7 degrees C). The theoretical simulation was verified and applied to situations beyond the range of experimental conditions. Damaged tissue comprised pyknotic cell nuclei and degenerated myofibrils. Corresponding volumes were found to be up to 10 times higher than the volume of iron oxide dispersion. CONCLUSIONS The data demonstrate the applicability of local magnetic thermoablation for therapy of muscle lesions in the long term.