Ultrasound is in the domain of sound waves of a certain wavelength inaudible for human ears. Using a converter, it can visualize organs on 2D still images or in motion and measure the flow properties (primarily speed) of fluids. Lately 3D computer imaging is also possible (such as ultrasound imaging of the fetus). The examination is harmless to the body and may be repeated without causing any side effects, thus widely used in diagnostics.