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Cardiac Magnetic Detection Based on Atomic Magnetometer
Cardiac Magnetic Detection Based on Atomic Magnetometer
December 17, 2023
Significance of cardiac magnetic signal detection
The human body's magnetic field can reflect information about various tissues and organs within the human body. Measurement of the human body's magnetic field can be used to obtain information about human diseases, and its detection effect and convenience have exceeded the measurement of the human body's bioelectricity. The size of the heart's magnetic field is on the order of a few tens of pT, which is one of the earliest magnetic fields studied by human beings, compared to the brain's. The atrial and ventricular muscles of the heart are the most important parts of the body.
Magnetocardiography (MCG) is the result of the complex alternating bioelectric currents that accompany the cyclic contraction and diastole of the atrial and ventricular muscles of the heart. Compared to Electrocardiogram (ECG), cardiac magnetic field detection is not affected by the chest wall and other tissues, and MCG can detect the cardiac magnetic field through a multi-angle, multi-dimensional sensor array, thus providing more information about the heart and enabling precise localization of cardiac heart foci. Compared to CT, MRI and other cardiac research techniques, magnetocardiography is completely radiation-free. Currently, the technology of Magnetocardiography is becoming increasingly mature, with more than 100,000 clinical applications, which are mainly reflected in the following aspects:
01 Coronary heart disease
Coronary heart disease is a common and frequent disease, according to statistics, at present, China's coronary heart disease patients have more than 11 million people. Coronary heart disease is the most common cause of death, and the number of deaths even exceeds the total number of deaths from all tumors. For coronary heart disease, MCG mainly detects myocardial repolarization inconsistency caused by myocardial ischemia. For example, Li et al. measured MCG in 101 patients with coronary artery disease and 116 healthy volunteers. The results showed that the three parameters of R-max/ T-max, R-value, and mean angle were significantly higher in patients with coronary artery disease than in normal people. Among 101 patients with coronary artery disease, the proportions of myocardial ischemia detected by MCG, electrocardiography, and echocardiography were 74.26%, 48.51%, and 45.54%, respectively, which showed that the diagnostic accuracy of MCG in patients with coronary artery disease was significantly higher than that of electrocardiography and echocardiography. This shows that the diagnostic accuracy of MCG in patients with coronary heart disease is significantly higher than that of ECG and echocardiography.
Reference：Int. J. Clin. Exp. Med. 8(2):2441-2446(2015)
Arrhythmia is defined as an abnormality of the cardiac impulse at the site of origin, the frequency and rhythm of the heartbeat, and any part of the impulse conduction. According to statistics, the number of arrhythmia patients in China is more than 20 million, and MEG can be used to accurately localize the lesions of arrhythmia patients. Ito et al. studied 51 arrhythmia patients, and by analyzing three parameters of the magnetocardiograms, they were able to determine the location of the different foci that caused the arrhythmia (right ventricular outflow tract, aortic sinus) with an accuracy of 94%.
Reference：Heart Rhythm, 11(9):1605-1612(2014)
03 Fetal Heart Screening
Every year in China, about 100,000-200,000 children are born with congenital heart disease. Currently, fetal ECG is often affected by the sebaceous glands, amniotic fluid and amniotic membrane on the surface of the fetus, and is unable to accurately obtain information on heart activity. Unlike fetal electrocardiograms, magnetic signals do not interfere with body tissues, making fetal magnetocardiograms the only means of detecting fetal cardiac activity during pregnancy, as they accurately reflect the fetal heart. Campbell et al. observed two singleton pregnancies and one twin pregnancy admitted with supraventricular tachyarrhythmias, and used MCGs to monitor the pregnant women's and fetuses' cardiac arrhythmias. MCG was utilized to monitor maternal and fetal arrhythmias and based on this, pharmacological treatment was carried out and the results showed that all three patients with fetal arrhythmias in the study were effectively treated.
With decades of development in cardiac magnetic technology, magnetometers can be broadly categorized into superconducting and non-superconducting magnetometers.
Superconducting magnetometers are based on the technology of magnetic flux quantization and the superconducting Josephson junction effect, and are the earlier magnetometers to enter clinical applications. At present, there are mature manufacturers at home and abroad, such as: the United States Cardio Ma, Germany SQUID AG, Finland Neuromag, China MANDI Medical, Cardiomag and so on.
Superconducting magnetocardiography requires a large magnetically shielded room and a large amount of liquid helium to maintain the superconducting state, and with the current global shortage of helium, the price of liquid helium is rising, resulting in extremely high operating costs, which greatly limits clinical applications. However, the clinical effectiveness of MRI is remarkable and scientists have been searching for alternatives.
Detection of adult human heart magnetism based on multi-channel atomic magnetometer
Atomic magnetometers are magnetometers with ultra-high sensitivity that have been developed in recent years. In 2012, scientists built a 4-channel array of ultra-sensitive atomic magnetometers (with a sensitivity of up to 6-11 fT/Hz1/2 per channel) using alkali-metal-based atomic magnetometers and successfully obtained adult magnetocardiograms in a magnetically shielded room.
Reference：Phys. Med. Biol. 57 (2012) 2619–2632
Since atomic magnetometer-based magnetometers have almost no operation and maintenance costs, they have the potential for large-scale clinical applications.In 2017, Genetesis, Inc. started the research and development of atomic magnetometer-based magnetometers, and subsequently launched the world's first atomic magnetometer-based magnetometer, CardioFlux™, which is now in clinical use.
Atomic magnetometer-based magnetometers have become an important development direction in the field of magnetometry, and atomic magnetometers, as their core components, further improve the sensitivity of magnetometry while effectively reducing operating costs. CIQTEK has developed and released the Quantum Spin Magnetometer (SpinMag-I) based on its profound technical accumulation and application practice in the field of quantum precision measurement.
The Quantum Spin Magnetometer (SpinMag-I) developed by CIQTEK utilizes the spin nature of the outer electrons of alkali metal atoms (Rb-87), and uses a pump laser as a means of manipulation to generate spin polarization in alkali metal atoms. Under the action of an external weak magnetic field, the alkali metal atoms undergo Larmor progression, changing the absorption of the detection laser, thus realizing highly sensitive magnetic field measurements. The quantum spin magnetometer is characterized by high sensitivity, small size, low energy consumption and easy portability, which will lead mankind to enter the quantum era in the field of magnetic sensing in scientific research, biomedicine and other fields in the future.