Sound waves are a form of mechanical energy. The number of vibrations per second of a sound source is called frequency, generally expressed in hertz, abbreviated as Hz. sound waves with a frequency of 2000 Hz or more are called ultrasound. Ultrasonic waves in the propagation process to reflect, refraction and the Doppler effect. When ultrasound waves propagate in a medium, sound energy attenuation occurs. Therefore, when ultrasound passes through some substantial organs, reflections of different shapes and intensities will occur. When the beam passes through tumor tissue, the absorption and attenuation of acoustic energy are also obvious. Due to the different physiological, pathological and anatomical conditions of human tissues and organs, the reflection, refraction and absorption of ultrasound attenuation are different. Ultrasound diagnosis is based on the number of these reflected signals, strength, distribution patterns to determine a variety of diseases. 40’s has been exploring the use of ultrasound examination of the human body, 50’s has been the study, the use of ultrasound so that the organs constitute the ultrasound level image, the early 70’s and the development of real-time ultrasound technology, can be observed in the heart and fetal activity. Ultrasound diagnostic equipment is not as expensive as CT or MRI equipment, can obtain any cross-section of the organ image, but also to observe the activities of moving organs, imaging fast, timely diagnosis, no pain and danger, belong to the non-invasive examination, therefore, the application of the clinic has been popularized, is an important part of medical imaging. The disadvantage is that the contrast resolution and spatial resolution of the image is not as high as CT and MRI. First, the physical properties of ultrasound ultrasound is a mechanical wave, generated by the mechanical vibration of the object. With wavelength, frequency and propagation speed and other physical quantities. Used for medical ultrasound frequency of 2.5 ~ 10MHz, commonly used is 2.5 ~ 5MHz. ultrasound needs to be propagated in the medium, its speed varies depending on the medium, the fastest in the solid, followed by the liquid, the slowest gas. In the soft tissue of the human body is about 150 m / s. The medium has a certain acoustic impedance, acoustic impedance is equal to the density of the medium and the product of ultrasound velocity. Ultrasound propagates in a straight line in a medium with good directivity. This is the basis for the detection of human organs with ultrasound. When the ultrasound transmitted through two different acoustic impedance of neighboring media interface when the difference in acoustic impedance is greater than 0.1%, and the interface is significantly larger than the wavelength, that is, the large interface, the reflection occurs, a part of the acoustic energy in the interface behind the neighboring media in the refraction of ultrasound continues to propagate, encountered another interface and then reflect until the exhaustion of acoustic energy. The reflected ultrasound is an echo. The larger the difference in acoustic impedance, the stronger the reflection, and if the interface is smaller than the wavelength, i.e., a small interface, scattering occurs. Ultrasound propagating in a medium also undergoes attenuation, i.e., the amplitude and intensity decrease. The attenuation is proportional to the attenuation coefficient of the medium, inversely proportional to the distance squared, and is also related to the absorption and scattering of the medium. Ultrasound also has a Doppler should (Doppler effect), the activity of the interface to the source of relative motion can change the reflected echo rate. This effect allows ultrasound to detect cardiac activity and fetal activity and blood flow. Second, the basic principles of ultrasound imaging human structure for ultrasound is a complex medium, a variety of organs and tissues, including pathological tissue has its specific acoustic impedance (Table 1-4-1) and attenuation characteristics. Thus, there are differences in acoustic impedance and differences in attenuation. Ultrasound into the body, from the surface to the deep, will pass through different acoustic impedance and different attenuation characteristics of organs and tissues, resulting in different reflections and attenuation. This difference in reflection and attenuation is the basis of the ultrasound image. The received echoes, according to the echo strength, with different light and dark points sequentially displayed on the screen, the human body can be shown on the cross-section of the ultrasound image, which is called acoustic image. The surface of the human organ is surrounded by a membrane, and the difference in acoustic impedance between the membrane and the tissue underneath is large, forming a good interface reflection, and a complete and clear peripheral echo appears on the acoustic image, thus revealing the contour of the organ. Based on the peripheral echoes, the shape and size of the organ can be determined. When ultrasound passes through the interior of different normal organs or lesions, the internal echoes can be anechoic, hypoechoic, or strong echoes of different degrees. No echo: The area where the ultrasound passes through is not reflected, and becomes a dark area without echo (black shadow), which may be caused by the following situations: ① liquid dark area: homogeneous liquid, with no difference in acoustic impedance or a very small difference, which does not constitute a reflective interface, forming a liquid dark area, such as blood, bile, urine, and amniotic fluid, etc.. In this way, blood vessels, gallbladder, bladder and amniotic cavity, etc. are liquid dark areas. Pathologic conditions such as pleural effusion, pericardial effusion, ascites, pus, pyelonephrosis, and fluid-containing cystic masses and encapsulated cysts also present as fluid dark zones, which are well permeable. In the dark area below the common echo enhancement, the appearance of bright light band (white shadow). ② Attenuated dark area: tumor, such as giant cancer, due to the absorption of ultrasound by the tumor, resulting in obvious attenuation and no echo, appearing attenuated dark area. (iii) Parenchymal dark area: homogeneous parenchyma with small acoustic impedance difference may appear as non-echoic dark area. Normal tissues such as renal parenchyma, spleen, etc. and diseased tissues such as renal carcinoma and hyaline degeneration can be manifested as parenchymal dark zone. Hypoechoic: parenchymal organs such as the liver, internal echoes are evenly distributed point-like echoes, in the event of acute inflammation and exudation, its acoustic impedance is smaller than that of normal tissues, and the transmittance increases, resulting in a hypoechoic area (gray shadow). Strong echoes: can be stronger echoes, strong echoes and very strong echoes. ① Stronger echoes: tumors with dense tissue or increased vascularity in parenchymal organs, with large acoustic impedance difference and increased reflective interfaces, resulting in enhanced local echoes and dense light spots or light clusters (gray shadows), such as carcinoma, leiomyosarcoma, and hemangioma. ② strong echoes: the internal structure of the medium is dense, and the neighboring soft tissues or liquids have obvious acoustic impedance difference, causing strong reflection. For example, bone, stone, calcification, can appear band or block strong echo area (white shadow), due to the poor sound transmission, the sound energy attenuation below, and the emergence of non-echo dark area, that is, acoustic shadow (acoustic shadow). ③ very strong echo: gas-containing organs such as lungs, inflatable gastrointestinal, because of the difference in acoustic impedance with the neighboring soft tissues is very large, almost all of the acoustic energy is reflected back, can not be transmitted, and there is a very strong light band. Third, ultrasound equipment ultrasound equipment types. Early application of amplitude modulation (amplitude mode), that is, A-type ultrasound, to reflect the change in wave amplitude echo. Gray-scale modulation type, that is, B-type ultrasound, the Department of light and dark spots to reflect the echo changes, in the shadow screen display 9 to 64 levels of gray-scale images, strong echoes of bright spots, weak echoes of dark spots. M-type ultrasound diagnostic as well as echocardiography used to detect the function of the human heart, echocardiography, ultrasound Doppler diagnostic (also known as the D-type diagnostic ultrasound), and so on. Doppler ultrasound diagnosis is to send ultrasound waves of a certain frequency to the part to be examined by the probe, if the interface moves toward the probe, the echo frequency increases, when the interface moves away from the probe, the echo frequency decreases. The difference between them is called the differential frequency, and the size of the differential frequency is proportional to the speed of movement of the interface. The Doppler signal detected to analyze and processed, amplified or detected, displayed on the oscilloscope screen, can be made into a variety of Doppler ultrasound diagnostic instrument. Such as Doppler auscultation type diagnostic instrument, ultrasound Doppler pulse meter, ultrasound Doppler blood flow measurement instrument and so on. It is a non-invasive method to examine the fetal heart, fetal and placental circulation, cardiovascular, cranial, cerebral, hepatobiliary, pancreatic, splenic, renal, ocular, abdominal and pelvic masses, as well as plasmapheresis, breast, thyroid, adrenal, and bladder, and peripheral vascular diseases. According to the different imaging methods, it is divided into static imaging and dynamic imaging or real timeimagimg. The former obtains static sonograms, image display a wider range of images, image is clearer, but the examination time is long, less application, the latter can be obtained in a short period of time, multi-frame images (20 ~ 40 frames / s), so you can observe the dynamic changes in the organ, but the image display range is small, the image is slightly less clear. Ultrasound equipment mainly consists of ultrasound transducer, i.e., probe (probe) and transmission and reception, display and recording, and power supply and other components. The transducer is an electroacoustic transducer, composed of piezoelectric crystals, to complete the generation of ultrasound and echo reception, and its performance affects the sensitivity, resolution and artifacts, such as interference.B-type ultrasound equipment, mostly pulse-echo type. Electronic line array multi-probe line square scanning, electronic phased array probe line fan scanning. In order to guide the perforation with the help of acoustic image, there are also perforated probe. Probe performance points 3.0, 3.5, 5.8MHz, etc.. The larger the MHz, the smaller the permeability. According to the examination part to choose the appropriate probe. For example, an 8 MHz probe is used for eye scanning, while for pelvic scanning, a 3.0 MHz probe is used. A single ultrasound device can be equipped with several alternative probes of different performance. A cathode ray tube is used for the monitor, and multi-frame cameras and video recorders are used for recording. Fourth, the USG image characteristics of the acoustic image is to light (white) and dark (black) between the different shades of gray to reflect the presence or absence of echo and the strength of the echo, no echo is a dark area (black shadow), a strong echo is a bright area (white shadow). The acoustic image is a level image. By changing the position of the probe, the sonogram can be obtained in any direction, and the movement of moving organs can be observed. But the scope of the image display is not as large and clear as X-ray, CT or MRI images. Fifth, the USG examination technique ultrasound exploration is mostly used in the supine position, but can also be used in the lateral position and other positions. The position can be changed during the exploration. The orientation of the section can be transverse, longitudinal or oblique section. The patient to take the appropriate position, reveal the skin, coated with coupling agent, in order to discharge the air between the probe and the skin, the probe close to the skin scanning, scanning to observe the image, freezing, that is, stopping the frame when necessary, line of careful observation, make a good record, and photographic or video. Attention should be paid to the size and shape of the organ, peripheral echoes, especially the posterior wall echoes, internal echoes, activity status, the relationship between the organ and neighboring organs and activity. Internationally, ultrasound diagnostic instruments are becoming more and more sophisticated with the rapid development of computers, communications, microelectronics, images and other related technologies. In recent years in the following aspects have been significantly developed: 1, ultrasound transducer: a. Composite materials, b micro-ultrasound transducer, c fine beam transducer, d high-density transducer, e a variety of intracavity probe and surgical probe. 2, all-digital ultrasound diagnostic device: since the early 1990s ATL company took the lead in launching the first all-digital B ultrasound, so far the world’s major several medical ultrasound diagnostic instrument manufacturers have almost launched their own all-digital beam-forming technology as the representative of the all-digital color ultrasound. Its development trend is multi-beam and high-capacity channels, improving the imaging speed and resolution. 3, sound beam above, 128 channels to 512 channels of products have been mass production. 4, several new imaging techniques: a Doppler energy imaging, b Doppler tissue imaging, c second harmonic and acoustic contrast imaging 5, three-dimensional imaging 5, remote and networking ultrasound image workstation.