Progress in MRI magnets

Since its appearance in the early 1980\´s, Magnetic Resonance Imaging (MRI) has taken its place as a major player in the noninvasive diagnosis of disease. It is the imaging modality of choice for detecting abnormalities of the brain, spine and musculoskeletal systems. It is on the verge of widespread application in diagnosis of cardiovascular disease and in image guided surgery. While permanent and resistive magnets are used for low field applications ("open" MRI) most systems use high field superconducting magnets making MRI the largest commercial application of superconductivity. The MRI magnet is the largest and most expensive component in the MRI system. Magnet configuration is the determining factor in MRI system architecture and directly connected to issues such as patient comfort, ease of siting, life cycle cost and functionality. All of these factors drive magnet requirements. Thus, MRI magnet requirements are determined by a combination of MRI system needs, technical requirements and market forces, plus the need for continuous reduction of both magnet-acquisition cost and total cost of ownership. Cost of ownership, in turn, includes siting, installation, operation and service. In this paper we trace the evolution of superconducting MRI magnet systems-taking note of the importance of advances in cryogenic technology and design practice-as they have responded to both market forces and competing magnet technologies.