The design and use of secondary shielding in MRI systems-experiments from 4 years of operation

Whole-body superconducting magnets are essential for MRI (magnetic resonance imaging) systems to perform spectroscopy and to get high-quality imaging. These magnets produce a large fringe field that interferes with other imaging equipment in a clinical environment. An approach to shielding magnets using primary shielding, which is comprised of a light-weight flux-return yoke near the magnet and secondary shielding in the desired direction, was developed. Primary shieldings for 0.5 T and 2 T were developed, built, and tested at the authors´ company, and installed at customer sites. It was found that this approach to shielding is the most cost effective in terms of using steel and achieving good homogeneity.