Development of Magnetocardiograph without Magnetically Shielded Room Using High-Detectivity TMR Sensors

Development of Magnetocardiograph without Magnetically Shielded Room Using High-Detectivity TMR Sensors

A magnetocardiograph that enables the clear observation of heart magnetic field mappings without magnetically shielded rooms at room temperatures has been successfully manufactured. Compared to widespread electrocardiographs, magnetocardiographs commonly have a higher spatial resolution, which is ex...

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Bibliographic Details
Published in:Sensors (Basel, Switzerland) Vol. 23; no. 2; p. 646
Main Authors: Kurashima, Koshi, Kataoka, Makoto, Nakano, Takafumi, Fujiwara, Kosuke, Kato, Seiichi, Nakamura, Takenobu, Yuzawa, Masaki, Masuda, Masanori, Ichimura, Kakeru, Okatake, Shigeki, Moriyasu, Yoshitaka, Sugiyama, Kazuhiro, Oogane, Mikihiko, Ando, Yasuo, Kumagai, Seiji, Matsuzaki, Hitoshi, Mochizuki, Hidenori
Format: Journal Article
Language:English
Published: Switzerland MDPI AG 06-01-2023
MDPI
Subjects:
Accuracy
Algorithms
Arrhythmia
Arrhythmias, Cardiac - diagnosis
Cardiac arrhythmia
Cardiomyopathy
Cardiovascular disease
Death, Sudden
Electrocardiography
environmental noise
Frequencies
Heart
Humans
Integrated circuits
Magnetic fields
Magnetic shielding
Magnetocardiography
Magnetoresistance
Magnetoresistivity
Multilayers
Myocardial Ischemia
Noise levels
Office buildings
Printed circuit boards
projection operation
Risk management
Room temperature
Sensor arrays
Sensors
Signal processing
signal space separation
Spatial resolution
Superconducting quantum interference devices
TMR sensors
projection operation
environmental noise
TMR sensors
magnetocardiography
signal space separation
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Summary:A magnetocardiograph that enables the clear observation of heart magnetic field mappings without magnetically shielded rooms at room temperatures has been successfully manufactured. Compared to widespread electrocardiographs, magnetocardiographs commonly have a higher spatial resolution, which is expected to lead to early diagnoses of ischemic heart disease and high diagnostic accuracy of ventricular arrhythmia, which involves the risk of sudden death. However, as the conventional superconducting quantum interference device (SQUID) magnetocardiographs require large magnetically shielded rooms and huge running costs to cool the SQUID sensors, magnetocardiography is still unfamiliar technology. Here, in order to achieve the heart field detectivity of 1.0 pT without magnetically shielded rooms and enough magnetocardiography accuracy, we aimed to improve the detectivity of tunneling magnetoresistance (TMR) sensors and to decrease the environmental and sensor noises with a mathematical algorithm. The magnetic detectivity of the TMR sensors was confirmed to be 14.1 pT on average in the frequency band between 0.2 and 100 Hz in uncooled states, thanks to the original multilayer structure and the innovative pattern of free layers. By constructing a sensor array using 288 TMR sensors and applying the mathematical magnetic shield technology of signal space separation (SSS), we confirmed that SSS reduces the environmental magnetic noise by -73 dB, which overtakes the general triple magnetically shielded rooms. Moreover, applying digital processing that combined the signal average of heart magnetic fields for one minute and the projection operation, we succeeded in reducing the sensor noise by about -23 dB. The heart magnetic field resolution measured on a subject in a laboratory in an office building was 0.99 pT and obtained magnetocardiograms and current arrow maps as clear as the SQUID magnetocardiograph does in the QRS and ST segments. Upon utilizing its superior spatial resolution, this magnetocardiograph has the potential to be an important tool for the early diagnosis of ischemic heart disease and the risk management of sudden death triggered by ventricular arrhythmia.
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content type line 23
ISSN:1424-8220
1424-8220
DOI:10.3390/s23020646