Evaluation of Temperature Increase with Different Amounts of Magnetite in Liver Tissue Samples

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Abstract
The biologic effects of magnetically induced heating effects using iron oxide, magnetite, were examined in vitro in liver tissue samples as a first step toward potential applications in cancer therapy. For the determination of the temperature profile around an iron oxide sample, a cylinder containing 170 mg of magnetite was constructed and placed into pureed liver tissue from pig, together with thermocouples of copper and constantan wires positioned at defined distances from it. Temperature measurements were performed during the exposure to an alternating magnetic field (frequency: 400 kHz; amplitude: approximately 6.5 kA/m) generated by a circular coil (90 mm of diameter). Moreover, variable amounts of magnetite (dissolved in approximately 0.2 mL physiologic saline) were injected directly into carrageenan gels. During the exposure to a magnetic field for 4 minutes the temperature increase was determined in the area of iron oxide deposition using a thermocouple. Additionally, variable amounts of magnetite were injected directly into isolated liver tissue samples (diameter: 20 mm; height: 30 mm) and exposed to a magnetic field for 2 minutes. The extent of the induced macroscopically visible tissue alterations (light brown colorations caused by heating) was examined by means of volume estimations. The degrees of cellular necrosis were investigated by histopathologic studies. The temperature profile around a magnetite cylinder revealed a significant decrease of temperature difference between the beginning and the end of heating, depending on increasing distance from the sample center. The extent of the temperature difference correlated with increasing heating time. No significant variations of temperature were observed at a distance of approximately 12 mm from the sample center. A good correlation (r = 0.98) between the injected amounts (31 to 200 mg) and the temperature increase since the start of heating (6.8-33.7 °C) in the area of iron oxide deposits was detected. The volume of damaged liver tissue was approximately seven times higher than the injected volume of iron oxide dispersion. Histologically different degrees of cellular necrosis were observed. The parameters determined in this article show that iron oxides are able to induce considerable heating effects in the surroundings. After an adequate optimization of the technical procedure, it is conceivable that heating properties of magnetites can be used in future cancer treatments.