A prototype 0.5 tesla whole body imaging magnet system

A prototype superconducting 0.5-T/1-m bore whole-body magnetic resonance imaging (MRI) system recently completed by GA Technologies Inc. for Ishikawajima-Harima Heavy Industries (IHI) is described. The magnet system makes use of the following key features: a precision-wound, profiled, 250-A coil, which exhibits high inherent field uniformity ( approximately 100 p.p.m./50 cm DSV); superconducting shim coils, which allow uniformity without passive bore shims; a novel cold mass support system for omnidirectional 5-g support with low heat leak; two concentric heat shields, cooled by an integral Gifford-McMahon two-stage refrigerator, yielding a net helium boiloff at 0.1 L/h with no liquid-nitrogen system; mechanically retractable, thermally decoupling current leads; and low-current-drift persistent-mode operation (0.085 p.p.m./h), with an internal protection circuit.