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Bio- Magnetic Imager / SQUIDS (John Zimmerman)

Bio- Magnetic Imager / SQUIDS (John Zimmerman)


We have been developing SQUID systems for various applications, with special emphasis on systems for biomagnetic applications. In 1987, Koyanagi and Kado fabricated and integrated a SQUID system made entirely of thin-film integrated SQUID. Research and development activities on multichannel SQUID system integration has been undertaken by various groups. The Superconducting Sensor Laboratory (SSL) project was one of the most significant of these activities. Such activities in North America and Europe have mostly been pursued by commercial groups, who have been fabricating commercial systems for end users. However, large-scale system distribution to end users is still impractical because of high costs and the lack of user-friendliness. As former members of the SSL project, some of us at the Kanazawa Institute of Technology began the development of SQUID systems aimed at overcoming previous problems such as high cost and the low level of user-friendliness. In this paper, we describe our concept of system integration and the level of the system’s sophistication.

Magnetic Field Imaging (MFI) is a non-invasive and side-effect-free cardiac diagnostic methode. It detects and records the electromagnetic signals that are associated with the heartbeat using a multi channel magnetic sensor array. The electric signals are known from the ECG and recordings of the magnatic signals are also known from Magnetocardiography (MCG). In comparison to MCG, MFI, among others, always records the whole relevant area above the chest of the person, is focused on clinical routine application and supplies convenient and easy to use parameters for the clinician based on images.

The general principal of MFI is based on two facts:

  • Cell activity in the human body is connected to electric activity (based on Galvani, Italy 1786).
  • Electric current is associated with a corresponding magnetic field (based on Ørsted, Denmark 1819).

The difference between the electric and the magnetic signals:

In comparison to the electric signals, which are influenced by the differently conductive tissue of the body and varying resistance of the skin before they can be recorded, the magnetic signals travel through the body almost without disturbance. The differences in the electric potentials, that are recorded by the ECG are directly depending on the inhomogenity and geometry of the torax, the magnetic signals outside of the torax depend primarily on the intracelular currents of the cardiac tissue and only secondarily on the secondary currents generating the elctric signal. Furthermore, the magnetic signals of so called vortex currents, which occur regularly in every heartbeat and include important information for an advanced and more accurate cardiac diagnosis (first theoreticaly discribed by Wikswo, J.), can be acquired with an MFI system, but can not be recorded electrically on the body surface (First experimental hint by Brockmeier et al 1994 and comprihensive demonstration Brockmeier et al 1997).

Patient during an MFI acquisition


MFI is safe, as it is an absolutely non-invasive, contact-free, radiation-free, purely passive recording of information from the electrical activity of the heart on a cellular level. MFI does not need any external magnetic field, no other external energy sources to be absorbed or reflected by the patient and no contrast agents.


The main fields of use are the risk stratification of ventricular tachycardia (VT) and the detection of stress induced ischemia. The MFI system can detect the onset of arrhythmic and ischemic diseases in a very early stage with high accuracy for both acute and asymptomatic patients.

Early Detection: Arrhythmia; Ischemia; Angina pectoris; Cardiac microvascular diseases

Direct diagnosis of heart function after myocardial infarction (MI) and surgery of heart transplantation

On-going Monitoring of patients with heart surgical intervention: Patients with a stent or who underwent a balloon dilatation; Post bypass patients; Post heart trans-plantation patients

As MFI is absolutely risk free and harmless for the patient, the procedure can be repeated without any negative effects for the patient, which gives the cardiologist the opportunity to observe a patient's progressive changes. The non-invasiveness of MFI makes it an ideal tool for the diagnosis of pregnant women as well as it can in addition detect the cardiac signal of an unborn child starting from the 4th month of pregnancy.