Systems can include at least one friction wheel configured to engage a catheter of an intravascular system such that proximal or distal motion of the catheter causes the friction wheel to rotate. A position sensor can include a reference element and a movable element, wherein the movable element is configured to move relative to the reference element in response to rotation of the at least one friction wheel. The position sensor can provide a position signal representative of the rotation of the at least one friction wheel. An intravascular processing engine can receive both the position signal from the position sensor and an intravascular signal from the catheter.