A first guidewire structure includes a medical guidewire extendable beyond a distal end of a medical instrument and having first and second segments, wherein the bending moment of inertia of the first segment is less than the bending moment of inertia of the second segment. A second guidewire structure includes a medical guidewire extendable beyond a distal end of a medical instrument having a mechanized guidewire drive assembly. The medical guidewire has an exterior surface including a repetitive series of spaced-apart surface elevation features. One example of surface elevation features is external threads. The spaced-apart surface elevation features are adapted for operable engagement with the mechanized guidewire drive assembly.
