An electrically conductive link (connection lead) or transmission line (13) including at least one transformer (41, 42; 83) for coupling at least two lead segments (51, 52; 81, 82) of the line (13) and for providing safety of the line when guided through a RF field. These lines are especially provided for use with a magnetic resonance (MR) imaging system and for connecting an electrical device (10), especially a catheter or another invasive device for the examination of a human body, to a connection unit (12) such as, for example, a power supply or control unit outside the examination zone (1) without imposing the risk of disturbances and/or destruction of the electrical device and/or the connection unit and of burning a patient (P) by a heating of the line when guided through RF fields.