CT examinations are generally classified into two types: plain CT and enhanced CT, both of which are frequently used in daily work. Enhanced CT includes conventional organ enhancement and vascular enhancement, and furthermore, CT can be divided into fixed CT and mobile CT, and from the perspective of molecular morphology and biology, CT can also be derived from PET-CT and MRCT and other comprehensive CT devices. Of course, there may be other classifications of CT, but those classifications are not encountered in daily clinical work, so normally, the two categories of CT that are routinely encountered are plain scan and enhanced.