Ultrasound refers to sound waves with a frequency >20,000Hz or more, which exceeds the upper limit of the hearing threshold of the human ear. The frequency of ultrasound commonly used in our medical diagnosis is 2-20MHz. According to the different forms of echo display, the diagnostic ultrasound instrument is divided into type A, type B, type M and type D. Among them, type B ultrasound its echo display is light dots, indicated by gray scale, which is a diagnostic method of examination based on a series of cut surfaces of the human body, also known as two-dimensional gray scale sonogram. What we usually call B-type ultrasound refers to an examination method, which is a non-invasive examination method and diagnostic technique that uses B-type ultrasound diagnostic instrument to examine the human body and diagnose diseases according to certain physical characteristics of ultrasound, mainly used to observe the size, structure, morphology and internal echogenicity of certain organs or lesions, surrounding tissue relationships, etc. It cannot be used to observe blood flow, and B-type ultrasound is the most basic examination technique.