Biomagnetic field detection using very high sensitivity magnetoimpedance sensors for medical applications

This paper demonstrates the performance of magnetoimpedance (MI) sensors for biomagnetic field recording. The rms noise of an amorphous wire MI sensor with 600 turns of pick-up coil was estimated as approximately 3 pT/Hz(1/2) at 1 Hz. Here, we demonstrate that this sensitivity is enough to clearly detect magnetic cardiogram signals. We also measured the biomagnetic field around a smooth muscle tissue sample taken from a guinea-pig. We discovered that the magnetic-field waveform of a small tissue sample is similar to the voltage waveform measured by a microelectrode array in a smooth muscle sheet sample. The results suggest that the localized biomagnetic field generated by smooth muscle cells can be detected by an MI sensor. We concluded that the MI sensor is a promising device for use as a noninvasive tool to test cell activity or function through magnetic-field measurement. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim