Ultrasound is what’s going on, this is a big problem, mainly from the concept of ultrasound, characteristics and imaging principles of science, first clarify the concept of ultrasound, ultrasound is a mechanical wave, refers to the frequency > 20000Hz or more, more than the upper limit of the threshold of human hearing sound waves, which is ultrasound. The frequency of sound waves at the threshold of hearing of the human ear is 20-20,000Hz, then more than 20,000Hz is ultrasound, below 20Hz is called infrasound. Commonly used medical diagnostic frequency is 2-20MHz, 1MHz = 10^6Hz, which means that the frequency of medical diagnostic ultrasound is very high. That medical ultrasound has what physical characteristics, mainly introduced the following six aspects: first, with directionality; second, interface; third, ultrasound field; fourth, absorption and attenuation; fifth, Doppler effect; sixth, the penetration and resolution of ultrasound. Having these characteristics lays a good foundation for the imaging of ultrasound. So how exactly does ultrasound form the image? Need to use an important part of the ultrasound instrument, that is, the probe. The probe is a device with the emission of sound waves and receive sound waves, the probe will receive the echo signal from different tissue interfaces after the emission of sound waves, these echo signals also contain acoustic information of different tissues, and then through the signal processing system after processing, in different forms of echo images displayed on the monitor for doctors to diagnose, which is ultrasound.