The difference between chest X-ray and CT is: 1. The former is just a simple X-ray through the chest once, so that the human chest tissues and organs on the screen to form a single image; CT can use X-ray on the human body for many tomography, the signal received by the detector into a digital signal, the attenuation coefficient of each pixel by the electronic computer calculations, and then reconstructed images, showing the tomographic structure of the various parts of the human body, the image of up to hundreds of sheets. 2. Chest X-ray can only show the approximate outline of chest organs and tissues, CT can clearly show the nuances of different tissues of the human body, but the radiation of chest X-ray is much lower than CT. Chest X-ray and CT are the use of X-rays have the characteristics of penetrating, fluorescence and photographic effect, so that the human body in the screen to form an image for the doctor’s diagnosis. CT has many advantages over ordinary x-rays, CT can distinguish the density of different tissues, in the form of multi-fracture images, clearly show the nuances of different tissues of the human body; while X-rays can only show the approximate chest organ tissue contours, but the radioactivity of CT is much greater than that of X-rays.