Instrument visualization in a magnetic resonance imaging environment

Magnetic resonance (MR) imaging has a number of characteristics that make it attractive for interventional guidance, including superior soft tissue contrast; the lack of ionizing radiation; the ability to provide functional information such as flow, perfusion, and diffusion; and the ability to monitor tissue temperature during ablation therapy. To date, MR scanning has played only a minor role in interventional guidance. One hindrance is that current interventional instruments are poorly visualized in an MR image. This article presents a number of approaches to making instruments visible in an MR scanning environment. Passive techniques, using signal voids, contrast agents, or susceptibility artifacts, as well as active alternatives, including optical triangulation, MR tracking, MR profiling, and active field inhomogeneity, are discussed.