The difference between low-density shadow and high-density shadow is mainly judged by the density difference of adjacent normal tissues. For example, if a low-density shadow is found in the brain on cranial CT, it refers to a low density compared with adjacent brain tissues, and this low-density shadow may refer to a brain infarction lesion. If a high-density shadow is shown on the cranial CT, the density is high compared with the density of the adjacent normal tissue, which may refer to hemorrhage or calcified foci. Therefore, the difference between low-density shadow and high-density shadow is mainly for the density difference with the adjacent normal tissues, which needs to be combined with the patient’s own clinical history to determine what kind of lesion this lesion tends to be.