Development of Compact Ultra-Low-Field MRI System Using an Induction Coil

Ultra-low-field magnetic resonance imaging (ULF-MRI) is attractive for MRI applications such as a concurrent system of magnetoencephalography (MEG) and MRI. We are developing a compact ULF-MRI system that can be combined with a small-animal MEG system. In this paper, we developed a detection method that uses an induction coil instead of a superconducting quantum interference device for the ULF-MRI. The induction coil has advantages such as being more robust, easy to handle, and flexible for designing. We fabricated an induction coil from a copper wire with dimensions of 29 mm x 39 mm x 29 mm (inner diameter x outer diameter x length). A capacitor was connected to increase the sensitivity by the LC resonance effect. The resonance frequency was 3 kHz, and the corresponding magnetic field density for MRI measurement was 70 μT. The detection coil was integrated with the compact ULF-MRI system and placed inside a magnetically shielded box. MRI measurement was demonstrated by using water phantoms with a total volume of 5.5 x 10
³
mm
³
. The size of the obtained image was 32 x 32 pixels for 30.2 mm x 30.2 mm. A clear shape of the water phantom was taken with this ULF-MRI system. This result shows the induction coil can be used for the compact ULF-MRI system.