3D image data of a skeletal portion is acquired. A location of a proximal portion of a tool is calculated and a location is derived of a distal portion of the tool with respect to the skeletal portion, with respect to the 3D image data. A display indicates the derived location. First and second 2D images of the distal portion of the tool are acquired from two different poses of a 2D imaging device with respect to the subject and registered with the 3D image data. The location of the distal portion with respect to the 3D image data of the skeletal portion is determined based on the registration and an identified location of the distal portion within the 2D x-rays. Based upon the determined location, the display updates the indicated location of the distal portion. Other embodiments are also described.
