For X-ray, CT, ultrasound, MRI, these common imaging tests, many people can not distinguish. Now, comparing the body to food, tell you how these tests play different roles. x-ray: like flattening bread to see the x-ray will pass through the body, encountering the obscured part, the negative will not be exposed, and the part is white after the film is washed. The biggest disadvantage of X-rays is that they are limited by the overlap and concealment of images of deep and shallow tissues, sometimes requiring multiple angles of X-rays. ct: like slicing bread to see the principle of CT examination is that X-rays will be layered through the body, followed by secondary imaging through computer calculations, just like slicing a piece of bread to see. Ultrasound: like picking a watermelon before knocking the principle of ultrasound is to use ultrasound to penetrate the body, when the sound waves encounter human tissue will produce reflected waves, through the calculation of reflected wave imaging. Just like picking a watermelon, knocking while looking shows the condition of the lesion. MRI: Shake it and see again The principle of MRI (magnetic resonance imaging) development is described below. The MRI machine uses a stronger magnetic field to make the magnetic lines of force of all water molecules in the human body in the same direction. At this time, the magnetic field of the MRI machine suddenly disappears, and the magnetic lines of force of the water molecules in the body suddenly return to the original randomly arranged 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. What kind of tests are used for each of the four imaging modalities? Doctors often order a variety of imaging tests: ultrasound, CT, and MRI. …… Many patients may question their doctor’s intention to order a high-cost test. In fact, doctors are based on different conditions to choose different imaging examinations. 1, traumatic bones – a coarse look at the X-ray film, a closer look at CT, MRI can not see a variety of trauma, if you suspect that the injury to the bone, the priority choice of X-ray photos, test results quickly and easily. If you want to observe further, you can choose CT. ultrasound, MRI for the bone cortex medulla is not very clear, generally do not choose. 2, cervical lumbar spine – the best choice of MRI, the second choice of CT cervical spondylosis, lumbar disc herniation and other intervertebral disc disease need to observe the intervertebral disc and the corresponding nerve roots, to better observe these soft tissues, the optimal choice is MRI. Similarly, for joint, muscle and fat tissue examination, MRI is also the first choice.3. Chest – a cursory look at X-rays, a closer look at CT, look at the lungs do not choose MRI X-rays of the chest can be a cursory examination of the heart, aorta, lungs, pleura, ribs, etc., can be checked for increased lung texture, lung calcification points, aortic node calcification, etc. CT chest examination shows a clearer structure and is more sensitive and accurate in detecting chest lesions than conventional X-ray chest films, especially for early lung cancer diagnosis. However, the radiation dose of CT examination is higher than that of X-ray. The application of MRI is very limited for the diagnosis of lung diseases.4. Abdominal pelvis – Except for the intestines, general ultrasound can check the 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 the liver, spleen, pancreas, kidneys, pelvic organs, etc. However, ultrasound is greatly disturbed by gas, for the intestines and other organs containing more gas, ultrasound diagnostic accuracy will be reduced. 5, heart – exclude coronary heart disease with CT, look at the heart function with ultrasound conventional heart structure and function of the examination, the information provided by the heart ultrasound has been more adequate, and simple and easy to use. With CT can check the coronary arteries, but coronary CT examination radiation is large, not suitable as a routine physical examination. The cardiac MRI is the “gold standard” for evaluating the structure and function of the heart.