Magnetic resonance imaging systems. A guide to the technology

Magnetic resonance imaging (MRI) has become firmly established as an essential imaging tool. Two characteristics of MRI--its ability to image soft tissue and its avoidance of harmful ionizing radiation--more than compensate for the costs, complexity, safety issues, and patient discomfort associated with it. Today, MRI is the modality of choice for a number of neurological and musculoskeletal indications and is being used for more applications than ever before. In some cases, MRI is supplementing existing techniques, such as vascular and cardiac imaging, while in others it is used to image physiologic processes that are invisible to any other imaging modality. MRI scanners are growing increasingly complex. As the technology develops, capabilities that were once available only to researchers are becoming routine in clinical applications. As a result, buyers now have more decisions to make when selecting a scanner than ever before. It is no longer simply a choice of field strength or whether to opt for an open or closed system. To gain an understanding of the important factors to consider when selecting MRI equipment, it is necessary to have a good understanding of how the systems work. In this article, we describe the operating principles of MRI systems. We also describe the major components of a system and the considerations involved when implementing MR imaging. Finally, we describe the issues surrounding the higher-powered three-tesla systems that are beginning to see commercial use.