An imaging system comprising: imaging apparatus for obtaining an image of an internal part of an object placed in an examination region of the imaging apparatus; a reference frame which carries a radiation sensing arrangement and is fixed with respect to a treatment position; a tool which is required to be accurately positioned with respect to the object when the object is in the treatment position; a radiation emitting arrangement associated with the tool which emits radiation for detection by the sensing arrangement to produce signals indicative of the position of the tool with respect to the reference frame; and display means for displaying said image of the object and utilising said signals produced by said sensing arrangement to provide a representation of said tool in said display at a position and orientation with respect to said image of the object corresponding to the position and orientation of the tool with respect to the actual object; characterised in that said reference frame and hence said treatment position is fixed in position with respect to said examination region.