Low-cost 7-Channel Magnetocardiographic System for Unshielded Environment

Abstract

The purpose of this work was to develop a low-cost ($150 000) magnetocardiography (MCG) system for use at cardiology clinics without magnetic shielding. The device consists of 7 channels – 4 signal and 3 reference ones. 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 estimated 2D current density distributions at a frontal plane.