sentences:  Until that time, it was believed that even a small amount of contrast agent within a coronary artery would be fatal.Until the 1950s, placing a catheter into either the arterial or venous system involved a "cut down" procedure, in which the soft tissues were dissected out of the way until the artery or vein was directly visualized and subsequently punctured by a catheter; this was known as the Sones technique.The percutaneous approach that is widely used today was developed by radiologist Sven-Ivar Seldinger in 1953.