Apparatus for performing a procedure using a tool configured to be advanced into a skeletal portion within a body of a subject along a longitudinal insertion path, and for use with:(a) a 3D imaging device configured to acquire 3D image data of the skeletal portion.(b) a 2D x-ray imaging device that is unregistered with respect to the subject's body and configured, while a portion of the tool is disposed at a first location along the longitudinal insertion path.
