4D ultrasound is a kind of B ultrasound. B ultrasound contains black and white B ultrasound, 2D ultrasound, 3D ultrasound and 4D ultrasound, while B ultrasound is a kind of ultrasound. There are four types of ultrasound: the first one is called A ultrasound, which is mainly used for industrial probe ultrasound, and is also the earliest ultrasound used for clinical diagnosis later. A ultrasound is a method to display tissue characteristics by waveform and identify the physical characteristics of diseased tissue. The second type is called B ultrasound, which is also commonly used in clinical practice as B ultrasound and two-dimensional color ultrasound. It is used to display the specific situation of the tissues being probed in the form of flat graphics, while the later developed three-dimensional and four-dimensional color ultrasound are also B ultrasound, but they are three-dimensional imaging formed by using digital reconstruction technology of computers. The third type is the M-ultrasound, which is mainly used for cardiac examinations. The fourth type is the D ultrasound, which examines blood flow through the Doppler phenomenon.