A catheter comprising:-a transmission line (104, 106, 924, 1202, 1302, 1902,), wherein the transmission line comprises a plurality of radio frequency traps (118, 318, 418, 518, 618, 718, 818, 918, 1018, 1202, 1404,) and-a cooling line (104, 304, 1200, 1900) for cooling the plurality of radio frequency traps with a fluid.