Ultrasonography, also known as acoustic imaging, is a technique that uses contrast agents to enhance the backscattered echoes and significantly improve the resolution, sensitivity and specificity of ultrasound diagnosis. With the improvement of instrument performance and the emergence of new acoustic contrast agents ultrasonography has been able to effectively enhance the two-dimensional ultrasound images and blood flow Doppler signals of myocardium, liver, kidney, brain and other substantive organs, reflecting and observing the blood perfusion of normal and diseased tissues, and has become a very important and promising development direction of ultrasound diagnosis. Some people regard it as the third revolution after two-dimensional ultrasound, Doppler and color flow imaging. The scattered echo intensity of blood cells is 1000-10000 times lower than that of soft tissues, and it is usually easy to identify the boundaries of the endocardium or large blood vessels in the heart cavity because it is “echo-free” in 2D. However, due to the presence of reverberation and the limitation of resolution, the endocardium is sometimes blurred and small vessels cannot be visualized. Ultrasonography is a technique to enhance the backscatter of blood by contrast agent to clearly display blood flow for the purpose of differential diagnosis of certain diseases. Because the contrast agent echo in the blood is more uniform than in the heart wall, and because the contrast agent flows with the blood, it is less likely to produce artifacts. Ultrasound Contrast Agents For different applications, different contrast agents are used. The most popular contrast agent is the microbubble contrast agent used to observe the state of tissue perfusion. Small bubbles less than 10 microns in diameter are usually referred to as microbubbles. The generation of contrast agents is based on the type of gas encapsulated within the microbubble. The first generation of contrast agent microbubbles contain air, and the second generation of contrast agent microbubbles contain inert gas. The first generation of microbubble acoustic contrast agent represented by Germany’s Schering (Schering) Levovist, which has a thick, easily broken shell of encapsulated air, poor resonance ability, and is not stable enough. When the bubble does not break, the harmonics are weak, while the harmonics are rich when the bubble breaks. Therefore, bursting microbubble is usually used for imaging. It uses the moment of bursting to generate harmonics of higher intensity. For cardiac applications, cardiac triggering is used, and for abdominal applications, manual triggering is used. The second generation of microbubble contrast agent represented by Italian Bracco (Bracco) Sonovue (Sonovue), which contains high-density inert gas matte hexafluoride, has good stability, the contrast agent has a thin and soft outer membrane, and the microbubble also has good resonance characteristics under the action of low sound pressure, vibrates without breaking, and can generate strong harmonic signals, which can acquire real-time harmonic images with lower noise, this The low MI sound beam can effectively preserve the microbubbles in the organ without being broken, which is conducive to having a longer time to scan each section. The development of a new generation of contrast agents has made real-time gray-scale perfusion imaging possible. The ultrasound contrast agents currently in clinical use in the United States are: Definity, Optison, Imagent three contrast agents; Sonovue has not yet been approved by the FDA. Domestic ultrasound contrast agents that have been successfully mass-produced and used in animal experiments are: (1) Clorica (CNUCA), which belongs to the phospholipid class of contrast agents, is divided into two types: one is a ready-to-use powder microbubble; one is a microbubble precursor substance, which needs to be prepared before use, but has not yet entered the clinical use stage. (2) perfluorochemical, belongs to the albumin type ultrasound microbubble agent, has entered the formal production stage High-quality new acoustic contrast agent should have the following characteristics: (1) high safety, low side effects; (2) uniform microbubble size, diameter less than 10 microns and can be controlled, can freely pass through capillaries, have similar hemodynamic characteristics of red blood cells; (3) can produce rich harmonics; (4) good stability. Microbubbles have three important properties such as good scattering, rich harmonic generation and rupture effect by acoustic pressure. At present, in addition to the rapid development of acoustic contrast agents for tissue imaging, targeted acoustic contrast agents with both diagnostic and therapeutic effects are also under research. Ultrasound imaging techniques Ultrasound imaging techniques include intermittent ultrasound imaging, energy contrast harmonic imaging, inverse pulse harmonic imaging, stimulated acoustic emission imaging, low mechanical index imaging, and contrast agent burst imaging, in addition to conventional contrast harmonic imaging. Regardless of the method, an ultrasound device capable of imaging must have sufficient bandwidth, high dynamic range, and be able to provide adequate parameters, such as: imaging time, MI and sound intensity, and real-time dynamic hard disk storage function. 1.Contrast blast imaging method When using first-generation contrast agents, in order to observe the information of contrast agent distribution in vascular organs and tissues, blast microbubbles are usually used to obtain rich harmonics. Blast contrast harmonic imaging is performed by cardiac wave triggering to obtain myocardial perfusion images; while in the case of abdominal organs such as the liver, manual triggering is used to obtain temporal images of contrast agent perfusion to the tumor. 2.Low mechanical index imaging When emitted ultrasound is used with a mechanical index MI below 0.15, it is called low mechanical index. The imaging performed using such ultrasound with an energy lower than that when the microbubble is broken is called low mechanical index imaging. This method allows for continuous harmonic imaging of blood flow and also reduces interference from tissue harmonics. This technique uses second-generation contrast agents. Clinical applications of ultrasonography The technique of cardiac acoustic imaging has developed greatly since its clinical application in the late 1960s, and the value of right heart acoustic imaging in the diagnosis of congenital heart disease has been well established. Myocardial perfusion sonography (MCE), in which a contrast agent containing microbubbles is injected directly into the peripheral vein into the coronary circulation to evaluate the integrity of the myocardial microcirculation, has also gradually entered the clinical arena, moving from a purely qualitative study to a quantitative one. The clinical application of sonography in other organs (liver, kidney, uterus, breast, etc.) has proven to be of great importance in the detection and qualitative diagnosis of tumors. Studies have shown that acoustic imaging is superior to conventional ultrasound and Spiral CT in the diagnosis of the number of liver tumors. especially in the detection of sub-centimeter lesions below 1 cm, acoustic imaging can be superior to or at least as sensitive as Spiral CT. Compared with CT and MRI, acoustic imaging possesses more superior features, such as good safety, no allergic reactions, real-time, and relatively low examination cost. The future of ultrasonography Future ultrasonography agents will be able to carry therapeutic drugs and genes for treatment, among others.