Design, Test, and Shimming of a 1.5-T Head-Only MRI Superconducting Magnet

As the core component of magnetic resonance imaging (MRI) system, superconducting magnet provides a high-intensity, stable, and homogeneous magnetic field background for the system. The strength, stability, and homogeneity of the magnetic field directly affect the imaging quality of MRI. This article presents the design, test, and shimming of a 1.5-T head-only MRI superconducting magnet developed by the Wuhan National High Magnetic Field Center. The magnet consists of seven primary coils and two shielding coils and is operated at an operating current of 510 A using bath cooling. The test has shown that the magnet reached the target field of 1.5 T directly after the first ramp-up without any quench. Under the magnetic field of 1.5 T, the magnetic field decay rate of the magnet is less than 0.02 ppm/hr. After three rounds of passive shimming, the magnet achieves a magnetic field inhomogeneity of 2.89 ppm over an imaging sphere within a diameter of 26 cm. The successful development of this magnet provides practical engineering validation for the lightweight technology of head-only MRI superconducting magnets.