1. System for the investigation of a body volume ( 3 ), particularly for diagnosing breast cancer, comprising an X-ray device ( 1 , 5 ) for generating projections (P, P′) of the body volume ( 3 ) from different directions; a data processing unit ( 7 ) that is coupled to said X-ray device and adapted to reconstruct sectional images (a, b, c, d, b′, b″) of the body volume ( 3 ) at different depths (z); an indication device ( 8 ) for interactively indicating a structure of interest ( 4 ) in a reference image (R) which is derived from one of said projections (P, P′) and/or sectional images (a, b, c, d, b′, b″), wherein the data processing unit ( 7 ) is adapted to estimate the depth (z) of said structure ( 4 ) in the body volume ( 3 ) with the help of said sectional images (a, b, c, d, b′, b″).