A simplified superconducting quantum interference device system to analyze vector components of a cardiac magnetic field

We have developed a 64-channnel superconducting quantum interference (SQUID) system that can analyze the vector components of a cardiac magnetic field, and that is more compact and requires fewer SQUID sensors and measuring circuits than existing systems. To adjust the position of the dewar, containing sensor array and liquid He relative to the chest, the bed is capable of three-dimensional movement. The magneto-cardiogram (MCG) data from the 64 channels are stored and analyzed using a personal computer. Each measurement site contains first-order gradiometers to detect the Bz component on the torso. The typical noise of the system in a magnetically shielded room (MSR) is less than 20 fT/√Hz. Tangential components at each measuring site can be calculated from the first-order gradient of Bz in the x- and y-directions. Two types of magnetic-field patterns of the Bz component and the Bxy tangential components are obtained at the same time. The position and distribution of a current source in the heart can be visualized through a two-dimensional projection using the analyzed tangential magnetic field