First, what is CT CT is the abbreviation of ComputedTomography, translated into Chinese means electronic computed tomography. CT is built on two principles: one is physical, which uses the properties of X-rays to produce different attenuated ray projections of human tissues and organs; the other is mathematical, which means that any object can be reconstructed from a collection of its numerous projections. According to these two principles, CT machine should have X-ray generation system, signal reception system and electronic computer processing system, whose core devices are X-ray bulb and high voltage generator (X-ray generation), detector (signal reception) and electronic computer (signal processing and image reconstruction), in addition to an auxiliary equipment (monitor, camera, etc.). The advantages of CT scan examination are: 1) the use of cross-sectional images, which can show the whole picture of an organ or tissue through the collection of multiple levels, just like cutting a carrot slice to show the internal center of the structure, thus avoiding the omission of lesions; 2) a high density resolution, for the detection of subtle The detection rate of lesions with density changes is significantly increased, and can be enhanced by intravenous injection of contrast to make further observation and identification; 3, the examination is quick and non-invasive; 4, there are convenient photos to carry, which is convenient for consultation and review. The shortcomings of CT examination are: 1. It is often difficult to show some isointense or small lesions and some early lesions limited to the cellular level; 2. 3. It is easy to produce artifacts on the moving organs and affect the observation; 4. It may affect the early embryonic development due to the use of X-ray. CT examination has very wide indications and can be said to be adapted to all systems, especially sensitive to diseases with density and morphological changes, such as inflammation, tuberculosis, tumors, trauma, vascular diseases and developmental abnormalities. CT has few contraindications, but should be avoided in women with early pregnancy and in patients who are highly sensitive to radiation. CT examination is divided into plain scan and enhanced scan. The plain scan is a general scan without injecting contrast into the blood vessels. The plain scan can be divided into axial (cross-sectional) scan and coronal scan according to the scanning position, and into fast continuous scan, target scan, thin layer scan and dynamic scan according to the scanning mode and purpose. In clinical practice, doctors will use the appropriate scanning method according to the condition. Enhancement scans are scans in which contrast is injected into the blood vessels. The intravenous injection of iodine-containing contrast media increases the density of the cardiovascular system and tissues and organs, facilitating the identification of tissues and organs as well as certain lesions. In order to obtain high quality images and facilitate diagnostic observation, it is important to note during CT examination: 1. Movement can cause artifacts and affect the observation, for dry patients and children should be given sedation. 2, to remove the metal foreign body of the scanning site, the metal foreign body of the scanning site can produce radiological artifacts and obscure the lesion. 3.When examining the abdomen, drink water or take 300-500 ml of 1.5-3% iodine solution to differentiate the stomach and intestines. After taking high atomic substances or barium meal should wait for its emptying before examination. 4, observation of the liver and gallbladder in the morning fasting is preferable. When examining pelvic lesions, it is better to keep enough urine. 5. Liver, kidney and heart failure should be ruled out when performing enhanced examination, and iodine allergy test should be done. 6.Patients who are critically ill, the elderly, children and those who perform enhancement should be accompanied by a companion. Interpretation of CT film CT film records a lot of information in CT examination, including text records and image records. The text records are usually displayed in English or Pinyin. The contents usually include: patient name, gender, age, CT number, whether to enhance, machine model, hospital name, date and time of scanning, scanning conditions (mA, kV and time), etc. The images are recorded in different degrees of black and white. Usually the first one is a positioning image, on which there are usually positioning lines, with the help of which the structure to be displayed in this layer can be judged. The rest are often cross-sectional images, and sometimes some coronal images and multidimensional reconstructed images may be taken upon request. The CT images are scanned in different layers and the number of images is different depending on the part of the scan and the content to be displayed, generally to meet the diagnostic purpose. Human tissues are, in descending order, bone, soft tissue, water and fluid, fat and gas.