There are many different types of CT examinations, including CT scan, CT enhancement, CT angiography, and CT perfusion scan, etc. CT scan is a very common examination method, and there are no special requirements for CT scan. CT angiography also requires contrast injection and mainly shows the condition of arteriovenous vessels, which is often used to examine aneurysms, aortic coarctation, pulmonary embolism, coronary stenosis, etc. In addition, CT perfusion scans are becoming more and more common in current clinical applications. Commonly, brain perfusion and pancreatic perfusion are used to understand the infarcts in the brain and islet cell tumors through the perfusion images of CT.