CT is used in a wide range of applications and is used in a high sense. According to different situations, different judgments, generally more role in the corresponding digestive system, urinary system, different examination preparation is completely different. The digestive system should be prepared with the appropriate fasting. Because only in the case of fasting, you can clearly understand the size, shape and distribution of the gallbladder, as well as the specific growth of the corresponding intestines, and timely detection of the corresponding occupational lesions. In the process of doing the examination of the urinary system, it is necessary to carry out the corresponding preparation for holding urine. For example, only in the case of holding urine, the bladder will be full, in order to understand the size of the bladder and the specific situation of the internal organs, especially timely detection of bladder stones, bladder polyps, and even bladder cancer, can greatly improve the probability of diagnosis of the disease. In addition to this, the examination of other systems, such as the nervous system, respiratory system, reproductive tract system, generally do not carry out these two preparations.