Echography is an examination method that uses ultrasound and allows the visualisation of certain parts of the body that are usually hidden from view. It is mainly used in obstetrics (imaging of the foetus) and in cardiology (heart and vessels), but also to perform a puncture or a biopsy, to visualize certain glands (thyroid) and most organs. Ultrasound, which has the ability to move through liquids, is stopped only by air and bones. Solid organs, such as the kidneys or liver, are particularly well studied through the use of ultrasound.