The CT examination is divided into 3 categories: plain scan, enhanced scan and CT imaging, and the examination area basically covers the whole body, including the cranium, the brain, the limbs, the trunk and the organs of the chest and abdomen. I. Fasting is required: 1. Enhanced CT: Enhanced CT requires intravascular injection of contrast agent before scanning, and some patients may have strong gastrointestinal reactions after drug injection, causing nausea and vomiting, so fasting is required for enhanced CT; 2. CT angiography: CT angiography refers to the imaging of an organ or structure before scanning, and is divided into two types: angiography and non-vascular angiography. Angiography is an intravenous injection of iodine contrast in the blood vessels, and non-vascular angiography is commonly used for myelography, which is a non-ionic water-soluble iodine contrast injected into the subarachnoid space of the spinal canal, and these two types of CT angiography also require fasting; 3. Second, no fasting: 1, cranial: that is, CT examination of the central system does not require fasting; 2, head and neck: refers to the area from the base of the skull to the entrance of the thorax, including the eyes, ears, nose and sinuses, pharynx, larynx, etc., CT examination of this area does not require fasting; 3, chest: chest CT examination of the lungs, ribs, sternum, heart, breast and other diseases, also does not require fasting; 4, extremities: such as the skeletal muscles of the extremities CT examination, also does not require fasting.