“A British six-year-old boy has become the first person in the world to have a heart valve widened using an MRI scan for guidance rather than X-ray imaging.”

http://news.bbc.co.uk/1/hi/health/8448787.stm

The catheters for the pulmonary valvuloplasty were stiffened with glass fibre instead of the usual steel wire. Being able to monitor with MRI means less radiation and additional information about soft tissues during the procedure.