Accuracy Improvement of Low-Invasive Temperature Measurement for Hyperthermia Treatment Using a Ferromagnetic Implant with Low Curie Temperature

We investigated a hyperthermia treatment method in which a ferromagnetic implant with a low Curie temperature (FILCT) is implanted into a malignant tumor and then a high-frequency magnetic field is applied outside the body. In earlier studies, we confirmed that the target temperature of the tumor can be noninvasively monitored by detecting changes in the magnetic field caused by changes in magnetic permeability. It was very difficult, however, to detect the FILCT temperature if the applied magnetic field was in an unstable state. Additionally, if the initial bias is higher, it is more difficult to detect the FILCT temperature because the resolution of the lock-in amplifier is reduced. In order to improve the accuracy of low-invasive temperature measurement, we formulated a method that reduces the drift in the pickup coil voltage caused by instability from the applied magnetic field. In addition, we experimentally confirmed that the influence of fluctuations in the applied magnetic field can be reduced by adjusting the initial bias value to close to 0 V.