An article on understanding the ultrasound equipment market and products

01

The characteristics and equipment classification of medical ultrasound

Medical ultrasound is an edge science that combines ultrasound in acoustics with medical applications, and is also an important component of biomedical engineering. The theory of vibration and waves is its theoretical foundation. Medical ultrasound includes two aspects: medical ultrasound physics and medical ultrasound engineering. Medical ultrasound physics studies the propagation characteristics and laws of ultrasound in biological tissues; Medical ultrasound engineering is a device designed and manufactured for medical diagnosis and treatment based on the laws of ultrasound propagation in biological tissues.

Ultrasound medical imaging instruments involve microelectronics technology, computer technology, information processing technology, acoustics technology, and materials science. They are the result of interdisciplinary and interdisciplinary collaboration and permeation between science, engineering, and medicine. So far, ultrasound imaging, along with X-CT, ECT, and MRI, has been recognized as the four major medical imaging technologies of contemporary times.

（1） Principles of Medical Ultrasound Imaging

When ultrasound propagates in different media, it produces waveform conversion, while the human body is a non-uniform medium composed of bones, air, body fluids, muscle tissue, etc. When ultrasound propagates within non-uniform tissues or from one tissue to another, reflection and projection are formed at the interface due to the different impedances of the two media (density and sound velocity of the media forming acoustic interfaces). The boundaries of different tissues can be determined based on the reflected ultrasound.

Meanwhile, as ultrasound propagates in a medium, the energy of the ultrasound gradually weakens with increasing distance. This phenomenon is called attenuation, which can be divided into three types: diffusion attenuation, scattering attenuation, and absorption attenuation. Scattering attenuation is closely related to the grain size, and absorption attenuation is also closely related to the characteristics of the medium. It can determine the composition of the tissue and can be used to determine its composition.

It should be noted that ultrasound is a type of sound wave that relies on a medium for propagation, and it has mechanical energy. Therefore, during the propagation process, it will inevitably interact with the medium, producing various effects. For example, when sound wave energy acts on a medium, it can cause high-frequency vibration of particles, resulting in changes in mechanical quantities such as velocity, acceleration, sound pressure, and sound intensity, thereby causing mechanical effects; Due to the absorption of ultrasonic energy by the medium, the temperature of the medium will increase, resulting in thermal effects; When ultrasound acts on a liquid, it causes a change in the internal pressure of the liquid, resulting in pressure or tension. When the tension reaches a certain strength, it can cause the liquid molecules to break and create holes close to vacuum, causing the so-called hole effect (also known as cavitation effect) and so on. When ultrasound acts on biological tissues, various physical effects mentioned above also exist, thus producing certain biological effects on biological tissues. For example, the absorption caused by the viscosity of biological tissues will convert a portion of sound energy into heat energy, causing a temperature rise in biological tissues. When ultrasound energy reaches a certain intensity, in addition to generating thermal effects, the result of cavitation effects may also cause destructive deformation of tissue cells.

Currently, it is widely believed that ultrasound poses little harm to the human body, but the dosage of ultrasound used for diagnosis is not considered to be the greater the better. The generally accepted dose should be less than the safe dose of 50 joules per square centimeter (J/cm2), and the maximum irradiation intensity should be less than 100mW/cm2. However, ultrasound energy is ultimately a mechanical energy, which is different from various harmful rays. The various examination and treatment methods achieved by ultrasound are still relatively safe.

（2） A Brief History of Medical Ultrasound Development

From the late 19th century to the early 20th century, piezoelectric and inverse piezoelectric effects were successively discovered, opening a new chapter in the development of ultrasound technology. In 1912, the British passenger ship Titanic collided with an iceberg while sailing near the North American coast and sank, resulting in the death of thousands of passengers and causing a devastating disaster that shook the world. During the First World War from 1914 to 1918, the French fleet was repeatedly attacked by German submarines and suffered heavy losses. These historical events have driven some scientists to focus on researching underwater detection and positioning technology. In 1917, French scientist Paul Langevin first used ultrasonic transducers mainly made of quartz crystals and invented Sonar (SONAR), which is a technology for detecting underwater submarines. In the 1930s, ultrasound was used for medical treatment and industrial metal testing, making ultrasound treatment the first to develop in medical ultrasound.

In 1942, Dussik and Fircstone first applied the principle of industrial ultrasonic testing to medical diagnosis. Diagnose cranial diseases using continuous ultrasound. In 1946, Fircstone et al. applied the reflection wave method for medical ultrasound diagnosis and proposed the principle of A-mode ultrasound diagnostic technology.

The first International Conference on Ultrasound Medicine held in 1949 promoted the development of medical ultrasound. In 1958, Hertz et al. first diagnosed heart disease using pulse echo method. M-mode echocardiography began to appear, while exploring the principles of B-mode two-dimensional imaging. In 1955, Jaffe discovered lead zirconate titanate piezoelectric material (PZT), an artificial piezoelectric material with excellent properties and easy manufacturing, greatly promoting the further development of industrial and medical ultrasound technology. In the late 1950s, continuous wave and pulsed wave Doppler techniques, as well as ultrasound microscopy, were introduced. In the 1950s, the use of pulse reflection to detect diseases achieved great success. It also laid the foundation for Doppler technology and B-type two-dimensional imaging.

In 1967, the real-time B-mode ultrasound imaging instrument was introduced, which was a significant advancement in B-mode imaging technology. Ultrasound holography, array transducers, electron focusing, and other technologies were widely studied. During this period, Doppler technology was further studied, and the use of spectral analysis to study blood flow was introduced. In the late 1960s, both the United States and Japan successfully developed piezoelectric polymer PVF2 (polyvinylidene fluoride) transducers.

In the 1970s, ultrasound diagnostic technology represented by ultrasound display developed rapidly, especially the emergence of digital scanning converters and processors (DSC and DSP), which pushed ultrasound display technology to a new level of strong functionality, high automation, and good image quality dominated by computer digital image processing.

In 1980, in the United States, the number of ultrasound imaging devices put into use began to exceed that of X-ray machines, ending the nearly century long history of X-ray dominated imaging diagnosis and declaring the entry of the "Year of Ultrasound Medicine". Dual function ultrasound diagnostic instruments and color blood flow imaging instruments have been successively launched, and multifunctional ultrasound imaging instruments are competing with various specialized imaging instruments. The structure of ultrasound probes and the spatiotemporal processing technology of sound beams are developing rapidly. Machine updates are becoming increasingly frequent.

In the 1990s, medical ultrasound imaging equipment developed towards two extremes. On the one hand, low-cost portable ultrasound diagnostic devices entered the market in large quantities, and on the other hand, they developed towards comprehensiveness, automation, quantification, and multifunctionality. Interventional ultrasound, fully digital computer ultrasound imaging, three-dimensional imaging, and ultrasound tissue characterization continued to make progress, leading to a sustained development trend in the entire ultrasound diagnostic technology and equipment.

In terms of probes, new materials and new types of transducers are constantly being introduced, such as high-frequency probes, cavity probes, and high-density probes, further improving the level and level of ultrasound diagnostic equipment.

（3） The characteristics of medical ultrasound imaging

At present, there are many types of ultrasound medical imaging diagnostic devices, and their outstanding characteristics are: ① no harm to the human body, which is also the main difference from X-ray diagnosis, so they are particularly suitable for obstetric and infant examinations; ② It is convenient to perform dynamic continuous real-time observation. In ultrasound diagnostic instruments above the middle range, there is often an image output interface, making it easy to retain, transmit, and communicate images in various forms (recording, printing, photosensitive imaging, computer storage, etc.) Due to its ability to use ultrasound pulse echo method for exploration, it is particularly suitable for the diagnosis of chest organs, heart, ophthalmology, and obstetrics and gynecology. On the other hand, it can better image bones or gas containing organ tissues such as lungs, which can complement the diagnostic characteristics of conventional X-ray From the comparison of information content, ultrasound diagnostic equipment uses computer digital image processing, which is currently slightly lower in terms of information content and clarity compared to X-ray film recording.

（4） Classification of ultrasound medical imaging equipment

1. A-type ultrasound diagnostic instrument: The transducer that generates ultrasound pulses is placed at a certain point on the surface of the human body, and the sound beam is injected into the body. The amplitude of the signal returned from the tissue interface is displayed on the screen. The horizontal axis of the screen represents the propagation time of ultrasound, that is, the detection depth, and the vertical axis represents the amplitude of the echo pulse, so it is called A-type. It is the most basic ultrasound diagnostic instrument used to measure the diameter of organs to determine their size, and can be used to distinguish some physical characteristics of diseased tissues. It is mainly used for space occupying lesions in the brain.

2. M-mode ultrasound diagnostic instrument: The echo information obtained by A-mode method is added to the CRT cathode (or gate) using brightness modulation method, and unfolded on the timeline to obtain the trajectory map of interface motion, especially suitable for the examination of moving organs such as the heart.

3. B-type ultrasound diagnostic instrument: also known as B-type ultrasound cross-sectional imaging instrument, it modulates the brightness of the display with the amplitude of the echo pulse, and the horizontal and vertical coordinates of the display correspond one-to-one with the position of the sound velocity scan, forming a brightness modulated ultrasound cross-sectional image. Therefore, it is called type B. B-type ultrasound diagnostic instruments can be divided into the following categories: ① fan-shaped scanning B-type ultrasound diagnostic instruments - including high-speed mechanical fan-shaped scanning, convex array fan-shaped scanning, phased array fan-shaped scanning, etc.; ② Linear scanning B-mode ultrasound diagnostic instrument; ③ Composite B-mode ultrasound diagnostic instrument - It includes a combination of linear scanning and fan-shaped scanning, as well as a combination of A-mode, B-mode, D-mode and other working modes, greatly enhancing the functionality of B-mode ultrasound equipment. It is currently the most common ultrasound instrument commonly used to detect tissue conditions.

4. D-type ultrasound Doppler diagnostic instrument: uses the Doppler effect to detect information about the moving tissues in the human body. Doppler detection methods are divided into continuous wave Doppler (CW) and pulse Doppler (PW). Suitable for observing the dynamic information of an organization.

5. C-type and F-type ultrasound imagers: The movement and synchronous scanning of the C-type probe form a "Z" shape, and the displayed sound image is perpendicular to the direction of the sound beam, which is equivalent to an X-ray tomographic image. F-type is a curved form of C-type, consisting of multiple cross-sectional images to form a curved image, which is approximately a three-dimensional image.

6. Ultrasound holographic diagnostic instrument: It follows the concept of optical holography and applies the interference and diffraction of two ultrasound beams to obtain information on the amplitude and phase of ultrasound, and uses laser to reproduce the amplitude and phase.

7. Ultrasound CT: Ultrasound CT is the transplantation and development of X-CT theory, which uses ultrasound beams instead of X-rays and reconstructs images from transmitted data similar to X-CT. Its advantages include: ① no radiation damage; ② Can obtain diagnostic information in a different form than X-CT and other ultrasound methods.