Development of a permanent magnet assembly for MRI.

A permanent magnet assembly for MRI (magnetic resonance imaging) has been developed using a high energy sintered Nd-Fe-B magnet. There are three types of magnet assembly for MRI: superconductive magnet, resistive conductive magnet and permanent magnet. Permanent magnet type does not require any liquid helium, electricity or cooling water, and can be intsalled in a small space. In spite of these advantages, however, the permanent type has not been widespread. The main reasons have been the difficulty of getting ppm order homogeneity and the tremendous magnet weight. However, a high energy Nd-Fe-B magnet developed in 1983 has made it possible to realize the permanent magnet type MRI. Using this magnet and investigating optimum configuration of pole pieces with shims, we obtained 30 ppm of Pκ/ Pκ deviation value in 35 cm diameter of spherical volume at the center of an air gap.