ABSTRACT
When an NMR imaging unit is to be installed in a hospital area, problems arise with the interaction of magnetic and Rf fields from the machine and the hospital environment which require safety considerations. In order to maintain these limits, NMR installations with high field superconductive magnets might require magnetic shielding. In addition, precautions must be taken for the possible occurrence of a quench in a superconductive unit. The coolant must be directed to the outdoor atmosphere of the room must be of sufficient volume to accommodate the coolant and still leave sufficient air volume at ground level to support life. A magnetic circuit of ferromagnetic material can reduce the power requirement for a resistive magnet considerably. The fringe fields are also largely reduced and can be neglected in many installation considerations. Permanent magnets bridge the field-strength gap between the resistive and medium-field superconducting NMR imaging systems.
