Development of Magnetocardiograph without Magnetically Shielded Room Using High-Detectivity TMR Sensors
Koshi Kurashima,
Makoto Kataoka,
Takafumi Nakano,
Kosuke Fujiwara,
Seiichi Kato,
Takenobu Nakamura,
Masaki Yuzawa,
Masanori Masuda,
Kakeru Ichimura,
Shigeki Okatake,
Yoshitaka Moriyasu,
Kazuhiro Sugiyama,
Mikihiko Oogane,
Yasuo Ando,
Seiji Kumagai,
Hitoshi Matsuzaki,
Hidenori Mochizuki
Affiliations
Koshi Kurashima
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
Makoto Kataoka
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
Takafumi Nakano
Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba-yama, Aoba-ku, Sendai 980-8579, Miyagi, Japan
Kosuke Fujiwara
Spin Sensing Factory Corporation, Research Center for Rare Metal and Green Innovation, 403 468-1 Aramaki Aza-Aoba, Aoba-ku, Sendai 980-0845, Miyagi, Japan
Seiichi Kato
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
Takenobu Nakamura
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
Masaki Yuzawa
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
Masanori Masuda
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
Kakeru Ichimura
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
Shigeki Okatake
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
Yoshitaka Moriyasu
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
Kazuhiro Sugiyama
Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba-yama, Aoba-ku, Sendai 980-8579, Miyagi, Japan
Mikihiko Oogane
Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba-yama, Aoba-ku, Sendai 980-8579, Miyagi, Japan
Yasuo Ando
Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba-yama, Aoba-ku, Sendai 980-8579, Miyagi, Japan
Seiji Kumagai
Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba-yama, Aoba-ku, Sendai 980-8579, Miyagi, Japan
Hitoshi Matsuzaki
Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba-yama, Aoba-ku, Sendai 980-8579, Miyagi, Japan
Hidenori Mochizuki
Device & Process Application Development Unit, Research & Development Center, Asahi Kasei Microdevices Corporation, Atsugi AXT Maintower 20F, 3050 Okata, Atsugi 243-0021, Kanagawa, Japan
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 pTrms 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 pTrms 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.
