Permanent magnets for magnetic resonance imaging

Several permanent-magnet structures for whole-body nuclear magnetic resonance diagnostics are described and compared. All provide a field of 1.5 kOe over working volumes of about 0.9 m
³
without the use of electrical solenoids or bulky power supplies. A previously proposed ferrite model now weighs more than 11 tons. By using more unorthodox configurations employing rare earth permanent magnets, the same performance can be attained with as little as 3.6 tons of material.