Apparatus is provided that includes a tissue anchor, which (a) includes a helical tissue-coupling element which has a distal tissue-penetrating tip at a distal end of the tissue anchor, and which is configured to be advanced into soft tissue, and (b) is shaped so as to define a longitudinal channel extending to the distal end of the tissue anchor. The apparatus further includes a depth-finding tool, which includes a radiopaque bead that is axially moveable along the channel so as to serve as a marker indicating a depth of penetration of the tissue-coupling element into the soft tissue.
