Embodiments hereof relate to a guidewire formed from an elongated shaft, at least a portion of the shaft having an outer layer, a plurality of channels formed through the outer layer, and an inner core. The outer layer is formed from a material non susceptible to erosion by an erosion agent and the inner core is formed from a radiopaque material susceptible to erosion by the erosion agent. When exposed to the erosion agent, core material adjacent to the channels is removed to form a pattern of integral radiopaque segments or markers with a plurality of voids therebetween. By controlling the location of channels and the rate of erosion of the core material, the pattern of integral radiopaque segments and voids allow for in situ measurement when viewed under fluoroscopy.
