When you go to the hospital, medical terms such as “CT”, “MRI”, “X-ray” and “B-ultrasound” are not unfamiliar to people. These terms are not new to people, but these similar-looking medical imaging devices often make people “confused”. Why do you use “CT” sometimes and “MRI” sometimes, because your condition has worsened? In fact, they work on different principles and have their own division of labor. It is a matter of concern how to do the correct and appropriate examination without wasting the examination cost. A preliminary understanding of the characteristics, advantages and scope of application of these devices can help patients save time and money. CT means X-ray computed tomography, which is a tomographic scan of a part of the human body with an X-ray beam to obtain a cross-sectional or stereoscopic image of the examined part of the human body. CT can provide complete three-dimensional information of the examined part of the human body, which can make organs and structures clearly visible and show lesions clearly. X-rays are highly penetrating rays that can penetrate the body. The principle of using X-rays for fluoroscopy or photography of the inside of the body is the use of the penetrating effect of X-rays. When penetrating the body, it is absorbed by calcium-containing components (bone), water (blood, etc.), and soft tissues (muscle) and is weakened, so that the basic shape of the area being examined can be presented. Unlike CT and X-rays, ultrasound examinations use the principle of ultrasound to produce echoes for examination. Ultrasound can propagate in a certain direction and can penetrate objects, and if it encounters an obstacle, it will produce an echo. people collect and display this echo on the screen through the instrument, which can be used to understand the internal structure of the object and assist in diagnosis. ultrasound is 2-dimensional ultrasound information, which constitutes a planar graphic and reflects the structure of the human body. With the emergence of color-Doppler ultrasound technology, color ultrasound (color B-ultrasound) emerged, i.e., color Doppler was added to black-and-white B-ultrasound. Color ultrasound also provides rich information on hemodynamics, and practical applications are widely valued and welcomed, and color ultrasound is often used in current clinical practice. MR, MRI, or magnetic resonance, is a biomagnetic spin imaging technique that uses the spin motion of atomic nuclei within an applied magnetic field to generate signals after excitation by radiofrequency pulses, which are detected with detectors and input to a computer and converted into images. Unlike CT and X-rays, the greatest advantage of MR is that it is not damaging to the body and there is no ionizing radiation damage. Compared to CT tomography, MR can obtain native 3D cross-sectional imaging in multiple directions, such as stereoscopic images of the brain and crestal medulla. It is particularly accurate for the diagnosis of bones, joints, cremaster, pelvic organs, prostate, bladder, uterus, ovaries, cardiac macrovascular lesions and myocardial infarction. For the examination of the lungs, the choice of X-ray or CT is superior to MR. For the examination of the liver, pancreas, adrenal glands, and prostate, MR is not superior to CT, but rather expensive. In addition, MR examinations are not recommended for patients with metal objects in their bodies, those who are less than 3 months pregnant, those with pacemakers, or those who are critically ill. Chest X-ray or CT Chest X-ray can examine the heart, lungs, mediastinum, ribs, pleura, and aorta, such as increased lung texture, calcified lung spots, and calcified aortic nodes. Compared to X-rays, CT chest examinations show a more pronounced clarity of structures and are more sensitive in detecting chest lesions and more accurate in showing lesions than conventional X-rays of the chest. CT chest examination is good for detecting minor lesions and hidden lesions and showing lesion characteristics, especially for early lung cancer diagnosis. However, the radiation dose of CT examinations is significantly higher than that of X-rays. In addition, X-ray is one of the important examinations in clinical orthopedics, and its effect is to check whether there are organic lesions in bone, crest and joints, to clarify the location, size, degree and relationship with surrounding soft tissues, and to provide reference for treatment. And CT can diagnose bone itself lesions, fracture or dislocation, bone joint and soft tissue lesions, etc. Check ultrasound for gallbladder diseases Ultrasound has a high degree of accuracy in the diagnosis of gallbladder diseases, such as gallbladder stones, with a general accuracy rate of over 95%, while CT has a lower diagnostic compliance rate. Since CT scans every 1-5 seconds, it is not easy to obtain accurate information for the examination of organs such as the heart, normal people whistle at least once every 3 seconds when calm, and abdominal organs affected by whistling, such as the liver and spleen, the patient has to pause whistling when doing CT examinations, and the young, mentally disturbed, and those with pulmonary insufficiency cannot cooperate and cannot be examined, while there is no such limitation for doing B-ultrasound. Ultrasound is the most commonly used method for clinical examination of biliary tract diseases, and can confirm the diagnosis of gallbladder stones, gallbladder inflammation, tumors, etc. Moreover, ultrasound has a higher accuracy rate for cirrhosis, fatty liver, splenomegaly, liver cancer, and intestinal lesions. In addition, the purpose of ultrasound examination during pregnancy is to determine whether the fetus grows in accordance with the gestational week, to determine whether the fetus has any malformation, and to understand whether the fetus is safe in the womb. CT is more accurate in diagnosing tumors than B-ultrasound. For small lumps of 1 to 2 cm, CT shows 88%, while B-ultrasound shows 48%; for kidney cancer, CT is 90% accurate, while B-ultrasound shows 44%. CT is quite accurate in showing kidney cancer and pelvic cancer, and can determine the size of the tumor, the extent of infiltration, and adjacent and distant lymph node metastasis. For liver and pancreas, CT can diagnose hepatocellular carcinoma, hepatic hemangioma, fatty liver, pancreatic cancer, acute pancreatitis, chronic pancreatitis, etc., while MR is suitable for examining primary liver cancer and other diseases. CT is superior to ultrasound in diagnosing kidney, adrenal gland, bladder and prostate diseases. CT can show not only the renal pelvis, calyces and bladder lumen, but also the renal parenchyma and bladder wall, and can diagnose adrenal tumor, subperitoneal It can diagnose adrenal tumors, subperitoneal hemorrhage, etc. MR can examine muscles and soft tissues. MR uses a completely different imaging principle than X-rays, and the resolution of soft tissues is far from that of CT and X-rays, and is mainly used to observe soft tissues in the spinal canal such as nerves and crestal medulla, so it can be used to detect and diagnose central nervous system diseases and posterior lumbar disc protrusion.