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Biomagnetic field measurement is a promising tool for the investigation of electrical activities in a living body. Room temperature (RT) magnetic sensors with an improved resolution such as magnetoresistance (MR) devices have been recently employed for the detection of weak magnetic fields, which were earlier detected solely using superconducting interference device magnetic sensors. The position, orientation, and sensitivity of each magnetic sensor in a sensor array must be precisely determined for accurate magnetic source analysis. We proposed a calibration method using an array of multiple coils, which is applicable to an RT magnetic sensor array. To demonstrate the validity of the proposed calibration method, we applied it to an MR devicebased magnetocardiography (MCG) system equipped with an L-shaped planar sensor array, which was newly developed for the simultaneous observation of both anterior and lateral sides of the body. The deviation of the sensor parameters from the designed values was estimated via calibration. The result of the marker coil localization test indicated that the calibration considerably improved the accuracy of the magnetic source analysis. Finally, we demonstrated a preliminary MCG measurement using the calibrated magnetic sensor array.

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In recent years, many kinds of magnetic sensors have been developed for biomagnetic measurement, such as magnetocardiography (MCG) and magnetoencephalography (MEG). However, it is difficult to evaluate their performance using only actual MCG or MEG measurements. In this paper, we propose the use of the calibrated MEG phantom for quantitative evaluation of magnetic sensors and present the experimental method. We choose a magneto-impedance (MI) sensor as an example of the magnetic sensor to be evaluated. The magnetic field distribution near the phantom was measured using the MI sensor and a signal source was localized with different averaging numbers and different signal source intensities. The results suggest that the MEG signal cannot be observed in the usual averaging time (i.e., 100), even when the sensor is located near the head; 4.0 mm of source localization accuracy can be achieved with 400-times averaging if the sensor noise decreases to 1/10. The use of the calibrated phantom, instead of examination with human subjects, is effective for quantitative evaluation of the performance of magnetic sensors.

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