X-rays: like flattening bread to see X-rays will pass through the body, encountering the obscured parts, the negative will not be exposed, and after the film is washed this part is white. For example, the bone of the thigh is round, but the film is flat, but you can see the filaments of the bone trabeculae. Like a piece of bread or a piece of cotton, you can not see the fiber texture inside, but deflated by hand will be clearer. Its biggest disadvantage is that the images of deep and shallow tissues overlap and hide each other, and sometimes a lateral X-ray is needed. CT: like slicing bread to see the principle of CT examination is that X-rays will be layered through the body, after the computer calculates the secondary imaging, like cutting a piece of bread into slices to see, the advantage is that it can be layered to see, and after the calculation can show more information about the tissue. B ultrasound: like picking a watermelon before knocking B ultrasound principle is to use ultrasound to penetrate the body, when the sound waves encounter different tissues, especially the tissue interface will produce reflected waves, ultrasound probe on one side to send out ultrasound, one side to receive reflected waves, and through the calculation of reflected waves imaging. It is like picking a watermelon, knocking and looking at the side to show the condition of the lesion. MRI: Shake it before you look The principle of MRI (magnetic resonance imaging) imaging is to detect changes in water molecules. The amount of water molecules in the body varies greatly from tissue to tissue, but the direction of the magnetic field magnetic lines for each water molecule is random. The MRI machine uses a strong magnetic field, so that the magnetic field of all water molecules in the body in the same direction, when the magnetic field of the MRI machine suddenly disappears, the magnetic direction of the water molecules in the body, suddenly returned to the original random arrangement of the state. Repeatedly apply the magnetic field and suddenly disappear, the MRI machine will get sufficient data and computing after imaging. Simply put, it is equivalent to shaking your hand to make the water molecules vibrate, then calm down and feel the vibration inside. Therefore, MRI is also jokingly referred to as a shake and see test. Why do doctors write tests like this? Doctors often prescribe a variety of imaging tests: ultrasound, CT, and MRI. …… Many patients are confused by this and question doctors who sometimes prescribe high-cost tests on purpose. In fact, doctors choose different imaging examinations according to different conditions. 1, trauma bone – a coarse look at the X-ray, a closer look at the CT, MRI can not see a variety of trauma, if you suspect that the injury to the bone, the X-ray results are fast and easy to obtain, is generally the first choice. Ultrasound and MRI are not as effective as X-ray based X-rays and CT for the bone cortex and medulla. 2, cervical spine and lumbar spine – best choice of MRI, second choice of CT cervical spondylosis, lumbar disc herniation and other intervertebral disc diseases need to observe the intervertebral disc and the corresponding nerve roots, to better observe these soft tissues, the optimal choice The best choice is MRI. Similarly, for joint, muscle and fat tissue examination, MRI is also the first choice. 3, chest – general understanding of the X-ray, detailed analysis of the CT, lung do not choose the MRI X-ray chest film can be a rough examination of the heart, aorta, lungs, pleura, ribs, etc., can check whether there is increased lung texture, lung calcification points, aortic node calcification, etc.. Compared with X-ray, CT chest examination shows clearer structures and is more sensitive than conventional X-ray chest film in detecting chest lesions and showing the accuracy of lesions, especially for early lung cancer diagnosis. High-resolution CT further increases the resolution of lung observation, which is significant for certain diseases (e.g. interstitial lung disease), but the radiation dose of CT examination is significantly higher than that of X-rays. MRI has very limited application for the diagnosis of lung diseases. 4, abdominal pelvis – in addition to the intestines, the general ultrasound can be checked Gallbladder and other abdominal organs are more affected by breathing, which in turn affects CT and MRI imaging, while ultrasound will not be affected by this. At the same time, ultrasound has a high diagnostic accuracy for liver, spleen, pancreas, kidney, pelvic organs, etc. With experienced ultrasonographers, the accuracy rate is as good as CT and MRI. However, ultrasound is greatly disturbed by gas, and for organs containing more gas such as the intestines, the accuracy of ultrasound diagnosis will be reduced. 5, heart – exclude coronary heart disease with CT, look at the function of the heart with ultrasound If it is a routine examination of the structure and function of the heart, the information provided by cardiac ultrasound has been more adequate, and simple and easy. With CT examination of coronary arteries, if no stenosis is found, coronary artery disease can be ruled out. CT examination of coronary arteries is more radiation-intensive and not suitable for routine physical examination. Although MRI is free of electromagnetic radiation, it is not as good as CT for coronary artery observation; cardiac MRI is the “gold standard” for evaluating the structure and function of the heart. When a myocardial infarction occurs, an MRI can accurately show the size of the atrioventricular cavity and the thickness of the ventricular wall of the heart.