An intervention instrument (60) employs a shaft (61) and a shaft tracker (62) partially or completely encircling the shaft (61) and movable to a primary tracking position along the shaft (61) between a distal tip and a proximal hub of the shaft (61). The primary tracking position is derived from a distance from an entry point of the distal tip into an anatomical region to a target location of the distal tip within the anatomical region. The shaft tracker (62) includes a primary position sensor (63) operable for tracking the shaft tracker (62) relative to the anatomical region at or offset from the primary tracking position.
