Abstract: A method and device are disclosed for improved minimally invasive vascular treatments. The procedure comprises introducing a mono-channel or multichannel catheter into a vein to be treated, under local anesthesia, where the multichannels can be essentially concentric. This special catheter receives an energy transmitting elongate member in a channel and a fluid in another channel, or in the case of a mono-channel fluid flows around the member. Fluids that can be used, but not limited to, are saline solutions, cooled saline solutions, liquids for vapor generation, vasoconstricting agents, anesthetic agents and/or a formulation containing an ingredient which can be activated by the applied energy. Anesthesia, where used, is introduced into the inside of the vein, thus eliminating the need of external or tumescent anesthesia. In addition, the previously mentioned substances can also be combined according to the treatment requirements for different purposes and effects.