Many people can’t tell the difference between X-rays, CT, ultrasound, and MRI, which are commonly used imaging tests. Now, compare the body to food and show you how these tests work differently.
X-rays: like squashing bread to see
X-rays will pass through the body and encounter an obscured area that will not be exposed on the negative, and the area will be white after the film is washed.
The biggest disadvantage of X-rays is that they are limited by the overlapping 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 pass through the body in layers, and then through computer calculations after the secondary imaging, like slicing a piece of bread to see. The advantage is that it can be viewed in layers, and after calculation, more tissue information can be displayed.
Ultrasound: like knocking a watermelon before picking it
The principle of ultrasound is to use ultrasound to penetrate the body, and when the sound waves encounter human tissue, it will produce reflected waves, and the reflected waves are imaged by calculation. It is like picking a watermelon, knocking while looking at it to show the condition of the lesion.
MRI: Shake it and see it again
The principle of nuclear magnetic resonance (MRI) imaging is described below.
The MRI machine uses a stronger magnetic field to make the magnetic lines of force of all water molecules in the body in the same direction, at which point 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 their 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 prescribe a variety of imaging tests: ultrasound, CT, and MRI. …… Many patients may question their doctors for intentionally prescribing high-cost tests. In fact, doctors choose different imaging tests according to different conditions.
1, traumatic bone – a rough look at the X-ray, 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, the results of the examination is fast and easy to obtain. If you want to further observation, you can choose CT. ultrasound, nuclear magnetic for the bone cortex medulla, etc. do not see very clear, generally do not choose.
2.Cervical spine and lumbar spine – the best choice of MRI, the second choice of CT
For cervical spondylosis, lumbar disc herniation and other intervertebral disc diseases that require observation of the intervertebral disc and the corresponding nerve roots, the best choice is MRI for better observation of these soft tissues. Similarly, for joint, muscle and fat tissue examination, MRI is also the first choice.
3, chest – a cursory look at the X-ray, a detailed look at the CT, look at the lungs do not choose the MRI
X-ray chest film can be a cursory examination of the heart, aorta, lungs, pleura, ribs, etc., can check for increased lung texture, lung calcification points, aortic node calcification, etc.
CT chest examination shows a clearer structure and is more sensitive than conventional X-ray chest film in detecting lesions in the chest and showing the accuracy of lesions, especially for early lung cancer diagnosis. However, the radiation dose of CT examination is higher than that of X-ray. The application of MRI for the diagnosis of lung diseases is very limited.
4.Abdominal pelvis – Except for the intestines, general ultrasound can investigate
Abdominal organs are more affected by breathing, which in turn affects CT and MRI imaging, while ultrasound is not affected by this. At the same time, ultrasound has a high diagnostic accuracy for liver, spleen, pancreas, kidney, pelvic organs, etc.
However, ultrasound is greatly interfered by gas, and the accuracy of ultrasound diagnosis will be reduced for organs containing more gas such as intestines.
5.Heart – Exclude coronary heart disease with CT, see the heart function with ultrasound
For routine heart structure and function examination, the information provided by cardiac ultrasound is more than adequate and simple to use.
With CT can check the coronary arteries, but the coronary CT examination radiation is large, not suitable for routine physical examination. Although MRI is free of electromagnetic radiation, it is not as good as CT for coronary artery observation, and cardiac MRI is the “gold standard” for evaluating the structure and function of the heart.