Suitable materials for insulator 36 include, but are not limited to, polytetrafluoroethylene (Teflon???, polyimides, polyamides and other insulating polymers known to those skilled in the art. [0047] Referring now to FIG. 4B, in one embodiment lumens 30 and apertures 30??? are of sufficient diameter to allow the free movement of guidewire 24 in catheter 18 so as to be able to controllably position