CT examination is widely used in clinical practice because of its simplicity, rapidity, safety, painlessness, high density resolution, clear anatomical relationship, and high detection rate and diagnostic accuracy of lesions. In the daily work of CT room, some patients often ask the doctor, “I have already done CT scan, why do I need to do CT enhanced examination? What is CT scan? What are its limitations? CT plain scan is the most basic CT examination without contrast injection. Although it can detect some lesions and even diagnose some diseases, CT plain scan cannot or cannot easily detect some lesions in certain areas, such as vascular malformations, early tumors and metastases, etc. CT plain scan also cannot reflect the blood supply of lesions, and cannot accurately determine the number and scope of lesions and other conditions for certain malignant lesions. How to do CT enhancement scan? CT-enhanced scan is a common means of CT examination and is a useful supplement to CT plain scan. It is a method of simultaneous CT scan examination after intravenous injection of a certain dose of iodine-containing contrast agent. What is the purpose of CT enhancement scan? The purpose of CT enhancement is to enhance the contrast between lesions and blood vessels and surrounding tissues, so as to facilitate the detection of lesions or to show the scope and nature of lesions more clearly, and to provide valuable information for qualitative diagnosis of lesions. In addition, it can also help to stage the tumor and determine the possibility of surgical resection. For example, for hepatocellular carcinoma, it only appears as a low-density lesion or no abnormality at all under CT plain scan, and cannot be distinguished from hemangioma and other lesions, but under CT enhanced scan, hepatocellular carcinoma can appear as a typical “fast-in-fast-out” sign, while hemangioma appears as a “fast-in-slow-out” sign. However, hepatocellular carcinoma can show the typical “fast-in-fast-out” sign under CT enhancement scan, while hemangioma shows “fast-in-low-out” sign.