High-Tc second-order gradiometer for magnetocardiography in an unshielded environment

Abstract

We have fabricated planar first-derivative gradiometers in which an asymmetric flux transformer patterned in a single-layer YBa2Cu3O7−x film is permanently bonded to a directly coupled magnetometer based on a dc superconducting quantum interference device (SQUID). The gradiometer base line is 48 mm. The common mode rejection of uniform magnetic fields is typically one part in a few hundred. The outputs of two such gradiometers are subtracted digitally to form a second-derivative gradiometer. Additionally, three orthogonal SQUID magnetometers are used to reduce the residual response to uniform magnetic fields to better than 100 ppm. The system is able to detect magnetic signals from a human heart in an unshielded environment.

A simplified HTc rf SQUID to analyze the human cardiac magnetic field

“…1,[3][4][5][6][7][8][9][10][11][12] The first-order axial gradiometer recording results are in less distortion than the second-order axial gradiometer with the same baseline for HT c SQUID MMCG system in a MSR. 1,6,12 The drawback of such gradiometers is impossible to keep in parallel with each other strictly. Considering the flexibility and stability of gradiometer, software gradiometer is an available way to obtain the high quality MCG signals that has been demonstrated by some impressive researches using various digital signal processing methods.…”

“…Recently, it has been shown that MCG provides practical and informative for diagnosing of the pre-excitation syndromes, ischemic heart disease (IHD) and the accurate localization of arrhythmogenic substrates and accessory pathways for catheter ablation or surgery with sufficient spatial accuracy necessary for clinical purpose, [1][2][3] this useful technique based on superconducting quantum interference device (SQUID) magnetometer, no matter on cryogenic or hyperthermia, have been developed. [4][5][6] Conceptually, MCG is not new. Actually, the first MCG recording system was carried out only after the invention of the SQUID in early 1970s.…”

“…6. Process of 3D Magnetic field, isomagnetic filed and current vectors in a healthy adult at T wave.…”

Second-order, high-temperature superconducting gradiometer for magnetocardiography in unshielded environment

“…Until present, first-and second-order HTS SQUID gradiometers, measuring axial or tangential fields, were demonstrated and MCG data recorded without magnetic shielding. [3][4][5] In these measurements, low-pass filters with a cutoff frequency of below 30 Hz were used to reduce the power line interference at 50 Hz, or a 60 Hz notch filter was used. 5 However, the frequency components of the MCG higher than 50 and 60 Hz contain significant information.…”

“…[3][4][5] In these measurements, low-pass filters with a cutoff frequency of below 30 Hz were used to reduce the power line interference at 50 Hz, or a 60 Hz notch filter was used. 5 However, the frequency components of the MCG higher than 50 and 60 Hz contain significant information. 2,6 For clinical diagnostics, a MCG system has to have a bandwidth wider than 100 Hz, so that further development is warranted.…”