Distal extremity 62 may be a polymer such as PTFE, FEP, polyimide, or Pebax, and is preferably reinforced with a metallic or polymeric braid to resist radial expansion when expandable member 24 is expanded. [0051] Preferably, proximal extremity 64 has a smaller transverse dimension than distal extremity 62 to accommodate the added width of guidewire tube 34 within the vessel lumen, as well as to m