DR that is, digital photography, CT that is, computed tomography, magnetic resonance, ultrasound, the difference is mainly the principle and scope of application of different, such as digital photography for the chest and skeletal system disease examination, computed tomography for the majority of parts of the body examination, both radiation, and magnetic resonance on many parts of the nervous system such as computerized tomography, ultrasound non-invasive, and so on. Principle is different: computed tomography is the use of rays on the examination part of the tomography, and digital photography is a kind of overlapping image, so the resolution of computed tomography is higher than digital photography. Magnetic resonance, on the other hand, utilizes an applied magnetic field to scan the body without radiation. Ultrasound, on the other hand, makes use of the physical properties of ultrasound, and through the study of the properties of sound waves in the propagation of human tissues and organs, it provides clinical diagnosis and treatment. It has the advantages of convenience, speed, economy and non-invasiveness, etc., and is widely used in the examination and treatment of substantial organs in the human body. The scope of application is different: Computed tomography has a high density resolution and is suitable for the examination of most parts of the body, such as the head, chest, abdomen and skeletal system. Digital photography has a narrower range of application and is mostly used to examine the chest and skeletal system. MRI has a higher resolution for soft tissues and is usually suitable for examinations related to diseases of the head, abdomen, and soft tissues. MRI is superior to computed tomography for examinations of the central nervous system, bladder, rectum, vagina, uterus, joints, and muscles.