Efficient Magnetic Gradient Field Generation With Arbitrary Axial Displacement for Magnetic Particle Imaging

The magnetic particle imaging method applies a magnetic gradient field featuring a field-free point (FFP) to determine the spatial distribution of superparamagnetic nanoparticles. Such a field is generated by two opposing electromagnetic coils, carrying currents in opposite directions. To achieve a large field of view, the FFP needs to be shifted in space. This can be realized by superimposing currents flowing in the same direction in both coils. For large displacements, the power loss increases drastically. In this letter, a new coil geometry is proposed, which is considerably more efficient for generating an FFP at off-center positions. It consists of four coils in which the currents are optimized to generate the required field at minimal power loss.