For X-ray, CT, B-ultrasound, MRI, these commonly used imaging examinations, many people can not distinguish clearly. Now, Xiao Bian compares the body to food and tells you intuitively how these tests play different roles.
X-ray: It’s like squashing bread
X-rays will pass through the human body and will not be exposed on the negative when they encounter the blocked part. After the film is developed, this part will be white. Like a piece of bread or a piece of cotton, you can’t see the fiber texture inside, but it will be clearer if you press it down with your hand. The biggest disadvantage of X-ray is that the images of deep and shallow tissues overlap and hide from each other, which sometimes requires multiple multi-angle X-ray films.
CT: Look like slicing bread
The principle of CT examination is that X-rays pass through the human body in layers, and then are computed by a computer for secondary imaging, just like cutting a piece of bread into slices. The advantage is that it can be seen in layers and more organizational information can be displayed after calculation.
B ultrasound: like picking watermelons, knock before picking them.
The principle of B-ultrasound is to use ultrasonic waves to penetrate the human body. When the sound waves meet the human body tissue, they will generate reflected waves, which are imaged by calculation. Just like picking watermelons, one needs to knock first before judging the situation.
Nuclear Magnetic Resonance: Shake and See
The magnetic resonance machine uses a relatively strong magnetic field to make the magnetic field lines of all water molecules in the human body in the same direction. At this moment, the magnetic field of the magnetic resonance machine suddenly disappears, and the magnetic field lines of water molecules in the human body suddenly return to the original randomly arranged state. Repeated application of magnetic field suddenly disappeared, and the MRI opportunity obtained sufficient data and imaged after calculation. Simply put, it is equivalent to shaking the water molecules by hand, making them vibrate, then calm down and feel the vibration inside. Therefore, magnetic resonance imaging (MRI) is also said to be a “shaking examination”.
What kind of examination are the four imaging methods applied to? When seeing a doctor, doctors often issue various imaging checkups: ultrasound, CT, MRI … Many patients will question the doctor’s intention to issue expensive checkups. In fact, doctors choose different imaging examinations according to different conditions.
1. Traumatic bone-Take a rough look at the X-ray film and examine various CT traumas. If you suspect that a bone has been injured, give priority to the X-ray film. The examination results are quick and easy to obtain. For further observation, CT can be selected. Ultrasound and nuclear magnetic resonance can’t clearly see the bone cortex and medulla, so they are generally not selected.
2. Cervical vertebra and lumbar vertebra-MRI is the best choice, CT is the second choice, cervical spondylosis, lumbar intervertebral disc herniation and other diseases need to observe intervertebral disc and corresponding nerve roots. To better observe these soft tissues, MRI is the best choice. Similarly, MRI is also the first choice for joint, muscle and adipose tissue examination.
3. Chest-A rough look at the X-ray film and a close look at the CT X-ray film can roughly check the heart, aorta, lung, pleura, ribs, etc. It can also check for increased lung texture, pulmonary calcification, aortic calcification, etc. Chest CT examination shows a clearer structure, and its sensitivity and accuracy in detecting chest lesions are better than conventional chest X-ray films, especially for the early diagnosis of lung cancer. However, the radiation dose of CT examination is higher than that of X-ray. Nuclear magnetic resonance is very limited in the diagnosis of lung diseases.
4. Abdominal Pelvic Cavity-Except intestinal tract, general ultrasound can check that abdominal organs are greatly affected by respiration, thus affecting CT and MRI, while ultrasound will not be affected. At the same time, ultrasound has high diagnostic accuracy for liver, spleen, pancreas, kidney, pelvic organs, etc. However, ultrasound is greatly disturbed by gas. For organs with more gas, such as intestinal tract, the accuracy of ultrasound diagnosis will decrease.
5. Heart-CT is used to exclude coronary heart disease, and conventional cardiac structure and function examination is used to check cardiac function. The information provided by cardiac color Doppler ultrasound is sufficient and simple. Coronary artery can be examined by CT, but coronary artery CT examination has a large amount of radiation and is not suitable for routine physical examination. Although nuclear magnetic resonance has no electromagnetic radiation, the observation of coronary artery is not as good as CT. Cardiac MRI is the “gold standard” for evaluating the structure and function of the heart.