MRI, like CT scans, is sometimes divided into two types of examinations: plain and enhanced. The main difference between plain scan and enhanced is that plain scan mostly does not require contrast injection, while enhanced requires contrast injection. If a plain scan reveals a problem, such as an occupying lesion or a hemorrhagic lesion that cannot be distinguished, an enhanced MRI is required. MRI uses a gadolinium-containing contrast agent that responds to MRI electromagnetic waves and can enhance tissue contrast in the body, such as in the case of malignant tumors, where a plain scan can see the difference between the tissue signal of the tumor itself and the normal tissue of the body. For example, liver cancer and hepatic hemangioma both show low signal in plain scan and T1-weighted image scan, and both show high signal in T2-weighted image scan, so it is impossible to distinguish whether it is liver cancer or hepatic hemangioma. In contrast, hepatocellular hemangioma can be accurately diagnosed by the slow progression and gradual filling of the lesion on the enhancement scan. After contrast injection, the tumor can be clearly distinguished from the normal tissue, which can help to find the tumor tissue and give qualitative determination of the tumor stage. In addition, enhancement scan can be used for angiography.