A guidewire includes a tapered core, an elongated non-radiopaque inner coil that is coincident with the core and extends over a distal portion of the core, and a radiopaque outer coil that fits over a distal end of the inner coil. The inner coil tapers between its proximal end and distal end, to form...http://www.google.ca/patents/US5551444?utm_source=gb-gplus-sharePatent US5551444 - Flexible guidewire with radiopaque outer coil and non-radiopaque inner coil
