**1.1 Definition of ultrasonographic method**

Ultrasound exploration (ultrasonography) is a very common diagnostic method. It is part of imaging procedures, without using ionizing radiations but ultrasounds (US) with usual frequencies of 2 - 5 - 12 MHz. Ultrasounds cross biological environments and are reflected at the demarcation limit between structures of different consistencies. The current procedure of ultrasound examination called "scanning" is based on the analysis of every plane from a region of interest in the human body. Each plane contains a high number of points with different brightness (within the limit of the gray scale used by the equipment) and their sum makes a defining "echostructure" for each organ. Ultrasound diagnosis is based on changes in tissue density due to pathological changes, resulting in echostructure transformation. Ultrasonography is an anatomical, hemodynamic and functional exploration.
