When it comes to imaging, what is the difference between X-rays and CT and MRI (i.e., magnetic resonance imaging)? What are the reasons why they are not considered to be substitutes for each other? Different imaging principles and different disease focus x-ray, CT, and MRI are several common methods of medical imaging in clinical practice, with different imaging principles, different examination methods, and different disease focus. Take an apple as an example: x-ray film is from the front of the apple fluoroscopy to the structure inside the apple, through the black and white color difference to present an image, which can roughly present the water, core or pulp; ct machine is developed from x-ray machine, flat-scan ct is generally cross-sectional scan, if still shoot an apple, ct examination is horizontal layer by layer to scan the apple, can display the different structures of the apple multi-level . Therefore, it presents an image of the cross-section of the apple, even the inside of the apple core can be seen; MRI is mainly an imaging technique that uses the signal generated by the resonance of the atomic nucleus within a high-intensity magnetic field and reconstructed by the image, which can directly make cross-sectional, sagittal, coronal and various oblique images of the body layers. When an apple is photographed with an MRI machine, the instrument can do various rotations, turning back and forth and left and right, and can also capture the tissue structure inside the apple. The three types of examinations have their own advantages and cannot be substituted for each other. x-ray is mainly used for the preliminary examination of some diseases, and is the first choice for the initial screening of diseases as it facilitates the discovery of tissues and structures with more obvious lesions, and is inexpensive. ct can clearly show the direction of blood vessels and vascular lesions, and is significantly more sensitive than ordinary x-ray for the examination of tumors. MRI has no damage to the human body, and ct has a certain radiation effect on the human body. MRI can obtain stereoscopic images of the brain and spinal cord. MRI is superior to ct in the diagnosis of cardiac tumors, morphology and function, while ct is superior to MRI in the imaging of the coronary arteries of the heart. At the same time, MRI is superior to ct in the examination of bladder, rectum, uterus, vagina, bone, joints and muscles, etc. MRI, like ct, is diagnostic imaging, and many lesions are still difficult to diagnose by images alone, especially for lesions of the gastrointestinal tract, which are not as good as endoscopy and can obtain both imaging and pathological diagnosis. MRI is not superior to CT for lung examination, and superior to CT for liver, pancreas, adrenal gland and prostate examination, but the cost is relatively expensive. Critically ill patients, those with pacemakers, prosthetic eyes, metal objects in the body, and those who cannot cooperate cannot undergo MRI. Why they are not interchangeable X-rays are the first choice for initial screening of disease X-rays are inexpensive and suitable for routine screening of most patients, especially for initial screening of disease. It has good diagnostic value for diseases such as displaced fractures, bone diseases with bone changes, bony lesions in joint areas, opaque foreign body retention, organic heart and lung diseases, and digestive system obstruction. In addition, radiographs can detect diseases in which the patient feels discomfort only when changing position. In particular, the power position film examination, which is still very rare in China, can replace X-ray examination with MRI. CT can show vascular lesions CT examination is significantly better than X-ray in showing cross-sections, especially for high-density tissues with clear images, and for measuring the distance between bony structures with high accuracy. CT can clearly show the direction of blood vessels and vascular lesions, and the inspection sensitivity of tumors is significantly higher than that of ordinary X-ray films. Moreover, multi-row spiral CT can perform three-dimensional imaging, which helps to display tissue and organ lesions in three dimensions. However, CT scan is limited by the different professional level of technicians and the limitation of scanning level interval, which cannot read the information of the examination site as a whole, resulting in a certain rate of missed diagnosis. In addition, the clarity and resolution of CT imaging of soft tissues is not high. MRI has a better effect on soft tissues. The biggest difference between MRI and X-ray and CT examinations is that there is no X-ray radiation during the examination, and the damage to the body is minimal. It is mainly used to detect soft tissue diseases. In orthopedics, it is mainly used to detect disc lesions, spinal cord lesions, meniscal lesions, inflammatory lesions and hemorrhagic lesions. MRI has a high sensitivity for vascular diseases. However, MRI also has disadvantages: first, the cost of general MRI examination is relatively expensive; second, the examination time for each part is long; third, the imaging accuracy of some bone tissues is not as good as CT; and the cost of dynamic MRI is several 10 times more than dynamic X-ray. Therefore, in the diagnosis of spinal fracture, spinal slippage, spinal deformity, spinal instability and other diseases, radiography is preferred; in determining whether a fracture is fresh or not, skimmed-phase MRI can be used; in the diagnosis of intervertebral disc lesions, especially cervical spondylosis, MRI is preferred, and in the examination of spinal cord morphology, spinal deformity, spinal tumor, spinal tuberculosis and other diseases, MRI is also preferred. CT has an irreplaceable advantage in the diagnosis of spinal fractures, spinal canal lesions, and arthrogryposis. In conclusion, the three tests are not interchangeable, and the more expensive the test, the better the problem can be detected. The key to which test is better depends on what part of the body is photographed. x-ray is now mainly used in the gastrointestinal tract, skeletal system and chest examination, and has good diagnostic value for diseases such as displaced fractures, bone diseases with bone changes, bony lesions in joints, opaque foreign body retention, organic heart and lung diseases, and digestive system obstruction. CT has increasingly shown its superiority in the diagnosis of chest diseases. Contrast-enhanced scans are usually used to clarify the presence or absence of masses or enlarged lymph nodes in the mediastinum and hilum, and the presence or absence of bronchial stenosis or obstruction, and play a major diagnostic role in the diagnosis of primary and metastatic mediastinal tumors, lymph node tuberculosis, and central lung cancer. With the development of technology, CT is of great importance for the examination of heart and blood vessels. In the heart, it is mainly for the diagnosis of pericardial lesions, the display of heart chambers and heart walls, and in the vasculature, calcification of coronary arteries, calcification of large vessel walls and aneurysm changes. MRI is significantly better than CT in showing craniocervical commissures, skull base, posterior cranial recess and spinal cord diseases, and has a high sensitivity for the diagnosis of central nervous system diseases, such as cerebral infarction, pituitary tumor, vascular malformation, trauma, congenital malformation, infection, etc. It is the best method for diagnosing spinal canal occupancy, stenosis, obstruction, disc degeneration, bulge and herniation. Experts recommend that x-ray, CT or MRI be considered depending on the situation (patient’s health, disease, economy, etc.). Generally, for patients who do not quite understand the cause, it is best to do x-ray first to see if there is any abnormality, and then consider further examination if no obvious abnormality is found or if abnormality is found and not quite clear. In short, the three are not interchangeable, and not the more expensive the test is, the more problems can be found. It is best to listen to the doctor’s advice during the consultation so that problems can be found early and accurately.