Ultrasound, is through the sound waves to penetrate the tissue, and can then be reflected within the tissue of the original image formation. In fact, the principle of ultrasound imaging, and the principle of optical imaging is similar, are imaged by reflection, except that sound waves are based on the characteristics of “waves”, while photons have a stronger “particle” nature, optical imaging images are clearer, more accurate identification.
Ultrasound imaging, why use ultrasound? The shorter the wavelength of ultrasound, the higher the frequency, the shorter the wavelength of the wave, the stronger the particle nature, the better the penetration, reflection accuracy, the clearer the image.
What is ultrasonic wave? Humans can hear sound waves in the frequency range of 20 Hz ~ 20,000 Hz, sound wave frequency greater than 20,000 Hz, people can not hear, greater than 20,000 Hz frequency of sound waves, called ultrasound. Ultrasound imaging, with ultrasound, people will not be able to hear and will not interfere with the hearing of the person being examined and the examiner.
Is ultrasound the only way to image? Can ordinary sound waves? Ocean exploration commonly uses low-frequency sonar to detect things in the deep strata of the ocean. Some blind people, after continuous training, are able to make their own sounds, like bats, and perceive the shapes of things around them through the reflection of their own sounds.
1. Ultrasound A, ultrasound B, and ultrasound M
Ultrasound B. Why is it called “B” ultrasound? Why is it called “B” ultrasound and not “A” ultrasound or “C” ultrasound?
If you answered “A”, congratulations, you are correct. There is indeed such a thing as an “A” ultrasound. The “A” ultrasound was first used for medical ultrasound examinations, but after the emergence of the “B” ultrasound, the “A” ultrasound was no longer used.
”A” ultrasound, is the emission of a beam of sound waves, the feedback back only acoustic impedance, no plane image, A ultrasound is now in the ophthalmology and other local areas are still used, other places basically do not use.
”B” ultrasound, is the beam of sound waves along a plane scan, the feedback is a plane image.
Therefore, it can be understood that the “A” ultrasound is one-dimensional, B ultrasound is two-dimensional.
Now are rarely used A ultrasound, because A ultrasound can only respond to the body acoustic impedance, while B ultrasound can feedback acoustic impedance into an image, look at the figure is always much easier than looking at the numbers, is not it.
The M ultrasound principle is the same as the A ultrasound, the imaging is also the same as the B ultrasound grayscale image, the difference is that the M ultrasound image, the response is a point of motion trajectory, mainly used to check the functional status of the moving organs, so only in the time to do cardiac ultrasound often used.
2. The difference between “black and white” and “color”
Whether “black and white ultrasound” or “color ultrasound” is done, the images of the parenchymal organs are actually black and white, and there is no clear difference. “Color” is not about making the image in color, but about indicating the blood flow signal.
There are only four colors in an ultrasound image: black, white (and gray from black to white), red, and blue. The red and blue colors mark the blood flow signal, where the red or blue color is the fluid flowing.
Red ≠ artery, blue ≠ vein
Ultrasound can only identify the presence or absence of fluid flow, with those that are oncoming showing up as red and those that are going farther away showing up as blue. Therefore, the color of blood flow seen on an ultrasound is not what distinguishes the arteries from the veins.
The theoretical basis of color ultrasound is called the Doppler effect. What does the Doppler effect mean? Standing by the railroad tracks, when the train across the street is whistling, we can hear the whistle getting sharper and sharper, and when the train is whistling away, we can hear the sharp whistle getting weaker and weaker. It’s not that the sound is louder when it’s closer together, but the frequency of the sound changes, and the sound that comes whistling, sounds, gets higher and higher in pitch, while the sound that goes whistling, gets lower and lower in pitch. In fact, the frequency of the sound from the siren does not change, but the frequency of the signal we receive changes because the source of the sound is moving, so the tone we hear changes. (If you are still confused, you can imagine the siren as a person with a machine gun shooting at you constantly, when he runs head-on, you are getting denser and denser from the bullets, when he runs further and further away, you are getting thinner and thinner from the bullets.)
Therefore, the red and blue colors seen on the color ultrasound may both be venous blood, or they may both be arterial blood, or they may be a mixture of multiple colors in the same vessel. However, color Doppler is more sensitive to the rapid flow of blood, so the blood flow signal seen on the ultrasound is mostly arterial, whether blue or red.
3. What is “systemic ultrasound”?
It is the ultrasound that systematically detects serious malformations in all organs and parts of the fetus. Systematic ultrasound can be two-dimensional, three-dimensional or four-dimensional, the latter two are just high-grade machines, but the key role is really played by the people who use the machines.
4.The difference between two-dimensional and three-dimensional ultrasound
Often people ask “two-dimensional ultrasound is good or three-dimensional ultrasound good”? This sentence is not strictly forbidden, the difference between A ultrasound and B ultrasound has been mentioned before, B ultrasound itself is two-dimensional, three-dimensional ultrasound is actually also made through two-dimensional B ultrasound, but the image data is input into the computer to reconstruct a little.
Two-dimensional ultrasound, like slicing, three-dimensional is to cut the slices arranged in order to overlap.
Imagine the feeling of slicing a radish, a piece of radish in front of you, non-professionals, it is difficult to recognize this is a piece of radish, but if all the radish slices overlap into a complete radish, you will definitely recognize it at once. This is the lure of 3D ultrasound for ordinary people.
The same with the radish slices for example, I give you a complete radish, if not sliced, and then the awesome cook can not imagine, this radish inside may be rotten, cut into slices is the significance of, we do not want to see the radish gorgeous appearance, but to see the radish inside there is no hole eye. That’s how professionals view the value of 2D ultrasound.
Therefore, whether you spend the money of 3D ultrasound or 4D ultrasound, the doctor always still has to identify the fine structures inside the organs through 2D images.
5.Difference between 3D and 4D
3D ultrasound and 4D ultrasound are both formed by computer reconstructed images on the basis of 2D. 3D is a three-dimensional image, while 4D is a three-dimensional image with movement. So do four-dimensional ultrasound friends pay attention, four-dimensional is animation, spend money to do four-dimensional, did not store animation CD, only play a three-dimensional picture, you the money is equal to spend in vain.
6, the timing of the major abnormality
The best time for a major abnormality should be around 20 weeks to 24 weeks. Why choose this time? On the one hand, too big is like a blind man feeling the elephant, easy to feel the leakage, on the other hand, too big when serious problems are found and need to induce labor, affecting the timing of induction of labor.
As a matter of fact, screening for malformations is a continuous process from early pregnancy to late pregnancy with every ultrasound examination. In order to screen for malformations more efficiently, we arranged for a relatively comprehensive and systematic “grand mal examination” in the middle of pregnancy – “systematic ultrasound”.
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