Medical Ultrasound
Ultrasound is not much different from the sound waves we are familiar with, except that we can't hear its "sound". When the frequency of sound waves reaches more than 20 kHz, which is beyond the range that normal people can perceive, this kind of sound waves is called ultrasound.
Similarly, if the frequency of a sound wave is lower than the range that humans can hear, it is an infrasound wave. So in other physical properties, ultrasonic waves are basically the same as sound waves.
Ultrasound/sound wave is a type of mechanical wave, there are longitudinal waves and pressure waves. It is transmitted through the vibration of particles, and the vibration of particles will continue to generate relatively high and low pressure areas, and its vibration direction and propagation direction are consistent, so the propagation of ultrasonic waves requires a medium.
Under different media, the speed of ultrasonic waves is different. For example, the speed in air is about 340 meters per second, in the human body, it is about 1540 meters per second, and the speed in vacuum is 0.
Ultrasound has a wide range of applications, especially in the medical field. As a non-radioactive method, ultrasound can help doctors to better diagnose patients.
1. How to generate ultrasound waves
The generation of ultrasonic waves and the generation of sound waves are based on the same principle. For sound waves, we usually use the telephone as an example.
When speaking, sound (mechanical energy) is converted into electrical signals (electrical energy) that travel to the other end, and then when listening, the electrical signals are converted back into sound. This is exactly the same as the process of generating and receiving ultrasonic waves, and their principle is the piezoelectric effect.
3. Propagation of ultrasound in the human body
As mentioned earlier, the speed of ultrasonic waves in the human body is about 1540 meters per second, which is actually an average value and is also the calibration speed used by ultrasonic instruments in most cases.
Ultrasound imaging relies on an estimate of ultrasound velocity, which has a direct impact on image quality. Then for different organs and tissues, the propagation speed of ultrasound is different.
For example, it is about 1510 meters per second in the brain, about 1560 meters per second in the liver and kidneys, 1570 meters per second in the muscles, etc. These are not very different from the average.
However, the ultrasonic speed in fat is only about 1440 meters per second. This speed difference makes the quality of ultrasonic images of obese patients significantly deteriorate. So in this case, the ultrasound will recalibrate or dynamically adjust the speed.
4. Introduction to the imaging of medical ultrasound
With the deepening of research and medical needs, ultrasound imaging has changed from only 1D to now 3D/4D. Ultrasound instruments can now also support a variety of imaging modalities to meet the needs of different patients and doctors. Below we will introduce you to several mainstream imaging modes.
A-mode: It is called 1D, which is the simplest mode. The detector emits a wave of ultrasonic waves in a certain direction, and the instrument presents the equation between the reflected signal and depth, and the image is similar to the signal we usually see on an oscilloscope.
A-mode was the main mode of early ultrasound instruments and is less used now, but it can also be used to guide high-energy waves to treat tumors during surgery.
B-mode: B means brightness here. In this mode, the ultrasound probe scans an area and generates a grayscale 2D image, which is one of the most commonly used modes today.
Stork Wireless Handheld Ultrasound - B mode
The lighter the color (white), the stronger the signal, usually the surface of the organ/tissue. The darker the color (black), the weaker the signal.
M-mode: M means motion here. In motion mode, the instrument performs fast B-mode scans and imaging, and doctors can see how organs are moving, which is especially important for heart-related diagnoses.
Stork Wireless Handheld Ultrasound - M mode
Doppler-mode: This mode is named after the use of the Doppler phenomenon to measure the velocity of moving objects. In Doppler mode, doctors can monitor blood flow and direction through ultrasound to determine possible lesions in blood vessels.
Stork Wireless Handheld Ultrasound - PW mode
Color Doppler: This mode can be simply understood as B-mode/M-mode + Doppler. On the basis of 2D grayscale images, the doppler mode and color calibration are used to display the position, blood flow, velocity and direction of blood vessels.
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