Magnetic Field Imaging (MFI) is a new method of diagnosis employed primarily in cardiology. It is, however, also suitable for use in other specialisms, such as neurology or foetal diagnosis.

MFI records the magnetic fields of the electrophysiological function of the heart and is able to display these graphically. MFI is the only electrophysiological method of diagnosis that is non-invasive and contact-free.

Physical bases of magnetic field imaging

MFI is based on two laws of nature:

1. Cell activity, particularly that of muscles and nerve cells, is always linked with electric activity.
2. Electric activity is always linked with a corresponding magnetic field.

Cardiological examinations using MFI are possible because the heart consists of many synchronously functioning, electrically active cells, which produce a sufficient total volume of cardiac electrical signals to enable MFI to function. This has particular benefits for the patient: the magnetic field can be recorded inductively (contact-free).

Unlike electrical signals, which are influenced by the varying electric conductivity of the tissue, magnetic fields leave the body almost intact. Magnetic recording, unlike electric recording, is reference-free and is therefore particularly suitable for recording low-frequency or static magnetic fields as well. In addition, the magnetic fields of such currents, which cannot be detected electrically on the surface of the body, can also be recorded magnetically. In this way, the vortex currents within the heart, which contain important information for cardiac diagnosis, can be recorded and displayed.

Use of MFI

MFI is used primarily in the diagnosis of ischemia and in the risk stratification of sudden cardiac death. By diagnosing ischemia at an early stage, an effective therapy can be indicated in good time to prevent a myocardial infarction. MFI enables the risk of cardiac arrhythmia (ventricular tachycardia, VT), which at its peak can lead to sudden cardiac death, to be identified at an early stage. Armed with this information, the attending physicians are then able to initiate further recording. However, there are also other areas of application for MFI in clinical research: early diagnosis of coronary heart disease in asymptomatic patients, monitoring patients who have had a stent implant or undergone a balloon dilatation procedure, monitoring patients after a bypass operation or heart transplant, examination of diabetes patients, as well as the diagnosis of cardiovascular diseases.

In the course of diagnosing ischemia, the MFI system can also display the electrophysiological effects of microcirculatory disturbances in the smallest vessels, thus facilitating focused, further treatment.

Components of the diagnostic system

MFI generally consists of three components: the sensor, data acquisition and data analysis system. The sensor consists of a 55-channel hexagonal sensor matrix with a diameter of 28 cm. This allows the entire relevant range to be recorded on the chest of a patient in one pass, which makes an extremely wide range of diagnostic questions possible.

So-called SQUIDs (Superconducting QUantum Interference Device), the most sensitive sensors available today, are used with MFI as individual sensor elements. This is important because the differences in the magnetic field to be recorded are about one million times smaller than the earth's magnetic field. The SQUID technology primarily developed by Cohen, Edelsack and Zimmerman in the late sixties and early seventies was further developed by Erné amongst others and can now be used in clinical routines today. After the well-known laser, the SQUID is the second quantum mechanical effect that can be used macroscopically. It is based on a microscopic superconducting ring with one or two Jospheson Junctions, which make this highly-sensitive magnetic detection even possible. The second important component of a MFI system is the data acquisition system, which amplifies the extremely weak signals, minimises environmental interference and prepares the signals for diagnosis. The item particularly important for the user is the analysis system. It is used to clearly and easily interpret data optimised for the respective clinical question in order to draw medical conclusions.

Clinical studies

The applicability of MFI was been convincingly established several times in the recent past in various studies. These results shall now be confirmed on a large patient population. In some multicentric clinical studies, research is currently being carried out on the diagnosis of ischemia and on the risk stratification of sudden cardiac death.