Low-cost 7-channel magnetocardiographic system for unshielded environment.

The purpose of this work was to develop a low-cost magnetocardiography (MCG) system for use at cardiology clinics, without any magnetic shielding. The device consists of seven channels: four signal and three reference channels. The signal channels are based on relaxation-oscillation SQUIDs. The reference channels are assembled into an orthogonal reference vector magnetometer (RVM). The 11-litre magnetotransparent helium cryostat allows operation for 5 days without refilling. With the 4-channel device, it is possible to perform measurements of magnetic maps in a standard 36-point grid so that only 9 spatial positions of the multichannel magnetometer are used; acquiring 30 s of data for each observation point takes about 10-15 minutes. Software was developed for the device adjustment, data acquisition, and data processing, including preliminary processing, MCG-mapping, and medical analysis. Digital filtering, adaptive noise compensation, and averaging are used to suppress magnetic noises. Cardiac sources were modelled with effective magnetic dipoles, and with estimated 2D current density distributions at a frontal plane.

Evaluation of magnetocardiography indices in patients with cardiac diseases.

The purpose of this work was to reveal pathological electrophysiological changes in patients with different cardiological diseases by means of magnetocardiographic (MCG) mapping. MCG mapping was performed with a 7-channel magnetocardiograph without a magnetically shielded room. We divided the 159 subjects studied into seven groups: 44 healthy controls, 42 patients with coronary artery disease (CAD), 11 patients affected with myocardiac infarction (MI), 11 with hypertension (HT), 14 with silent ischemia (SI), 13 with heart failure (HF), 14 with fibrillation (FB), and 10 patients after stunning of coronary arteries (ST). All patients were examined using a standard 12-lead electrocardiogram (ECG), biochemical analyses, and loading tests (bicycle-ergometry); some were also studied by holter monitoring, echocardiography, electrophysiological test, and coronary angiography. Morphological and correlation analyses of MCG maps were performed. Moreover, a number of quantitative MCG indices, which reflect the distribution of the excitation in the heart, were proposed. We observed that some indices demonstrated efficiency in recognition of pathologic activity for 5 diseases: CAD, MI, HT, HF, SI and FB.