Biopsy cannula adjustable depth stop

A biopsy system with a grid plate used as either a lateral or medial compression plate of a localization fixture used with a breast coil includes a rotatable guide cube that may be inserted into a desired rectangular recess in the grid plate after rotating to position a selected guide hole in the desired spatial orientation. Versions of a guide cube include those rotatable in two axes to provide additional hole positions, angled holes, enlarged circular holes that function with a rotating guide to support a noncircular biopsy instrument cannula (e.g., trocar/sleeve combination, core biopsy probe of a biopsy device) for rotation. A rotating guide may have an unlocked state for easily sliding to a selected longitudinal position thereon. Thereafter, the rotating guide is locked to serve as a positive depth stop (e.g., quarter turn locking elastomeric rings, triangular and scissor clips, and shutter depth stops).