A magnetic resonance imaging (MRI) system includes an interventional instrument and a switched, segmented transmission (Tx) line which ensures safety during an MRI protocol while the interventional instrument is located in the system. The transmission line includes at least two electrically conductive Tx line segments separated by a non-conductive gap. An electrically conductive bridge, having an open and a closed state, and a parallel connected impedance bridge, having a known impedance which suppresses RF current between the line segments, bridge the non-conductive gap. A measurement unit measures the impedance across the Tx line while the conductive bridges are open. The line segments are verified to be decoupled if the measured impedance of the line is substantially equal to that of the impedance bridge.
