Imaging tests may be helpful in diagnosing prostate cancer, pinpointing its location, and determining how advanced it is (its stage). Magnetic resonance imaging (MRI), for example, can be helpful in staging. This test uses a magnetic field to produce pictures of structures inside the body. Another imaging test, transrectal ultrasonography (TRUS) uses sound waves to create pictures. However, doctors generally use it to guide a biopsy, not for screening or diagnosis.