There are two conditions for contrast to work: 1, a very suitable contrast agent is needed, the contrast agent is generally a chemical substance, such as the commonly used barium or iodine. After entering the body, the contrast agent will not be absorbed by the body, and at the same time it forms a strong contrast with the density of the human tissue, so it can reveal the image of the part where it is located; 2, need to emit rays or imaging equipment that can make the body appear, such as commonly used X-rays, CT, nuclear magnetic and even ultrasound, etc., which are used to display the human tissue imaging equipment. With these two conditions, the imaging can be performed.