Feasibility of New Heating Method of Hepatic Parenchyma Using a Sintered MgFe2O4 Needle Under an Alternating Magnetic Field

BackgroundMagnetic metal particles such as magnesium ferrite (MgFe2O4) induce heat energy under an alternating magnetic field that was produced by electric current. We have developed a new heating device using a sintered MgFe2O4 needle under an alternating magnetic field. This device can repeatedly heat target tissue at lower temperatures than that for radiofrequency ablation therapy. This study aims to assess whether the new heating device has the ability to heat rat liver tissue.MethodA small needle made from MgFe2O4 particles was prepared by sintering at 1100°C and inserted into rat liver tissue. The rat liver was then heated under an alternating magnetic field, 4 kA/m, for 30 min. We measured the temperature of rat tissue during the heat treatment, and sequentially evaluated histological changes and hepatocyte cellular activity after heat stimulus by using nicotinamide adenine dinucleotide diaphorase staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining.ResultsThe mean temperature of the liver tissue during heating was 60.7 ± 1.1°C. Immediately after heating, nuclei of the hepatocytes were hyper-chromatin, with hepatocytes negative for nicotinamide adenine dinucleotide diaphorase activity in the heat-injury area. The injury area spread progressively until 3 d after heating, when the area was surrounded by fibroblasts, with hepatocytes positive for terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining.ConclusionsThis is the first time that a ferromagnetic metal heating device under an alternating magnetic field has achieved a temperature beyond 60°C and led hepatocytes to complete cell death. This device would be of future use as a local heat-treatment for human liver cancer.