Brief introduction of ultrasonic imaging

Directory 1 Pinyin 2 English Reference 3 Overview of 4 USG imaging basic principles and equipment 4. 1 Ultrasonic physical characteristics 4.2 Basic principles of ultrasonic imaging 4.3 Ultrasonic equipment 5 USG image characteristics 6 USG inspection technology 7 USG image analysis and diagnosis clinical application 8 USG diagnosis 1 Pinyin chāo shēng chéng xiàng

2 English reference USG

Overview Ultrasound is a sound wave that can be heard by normal human ears, and its frequency is above 20,000 Hz. Ultrasonic examination is an examination method that uses the difference between the physical characteristics of ultrasonic waves and the acoustic characteristics of human organs and tissues to display and record in the form of waveforms, curves or images, so as to diagnose diseases. In the early 1940s, we explored the use of ultrasound to examine the human body. In the 1950 s, we studied and used ultrasound to make organs form ultrasonic images. In the early 1970s, we developed real-time ultrasound technology to observe the activities of the heart and fetus. Ultrasonic diagnostic equipment is not as expensive as CT or MRI equipment, and can obtain images of any cross section of organs and observe the activities of moving organs. It is a non-invasive examination with fast imaging, timely diagnosis, no pain and danger. Therefore, it has been widely used in clinic and is an important part of medical imaging. The disadvantage is that the contrast resolution and spatial resolution of the image are not as high as CT and MRI. This paper only introduces gray-scale ultrasonic imaging.

Ultrasonic imaging is to scan the human body with ultrasonic sound beam, and obtain the image of internal organs by receiving and processing the reflected signals. There are many kinds of ultrasonic instruments in common use: Type A (amplitude modulation type) displays the strength of reflected signal with amplitude and displays an "echo map". M-shape (spot scanning type) represents the spatial position from shallow to deep in the vertical direction, and represents time in the horizontal direction, showing the motion curve of the spot at different times. Both of them are one-dimensional displays, and their applications are limited. Type B (brightness modulation type) is the ultrasonic section imager, referred to as "B-ultrasound". The intensity of the received signal is represented by light spots with different brightness. When the probe moves along the horizontal position, the light spots on the display screen also move synchronously along the horizontal direction, and the tracks of the light spots are connected into a cross-sectional view of ultrasonic sound beam scanning, which is two-dimensional imaging. B-ultrasound is widely used in clinic because of its clarity, intuition and strong sense of hierarchy. As for the D-type, it is made according to the principle of ultrasonic Doppler, and the C-type displays the sound image perpendicular to the cross section of the sound beam in a scanning way similar to that of a television. In recent years, ultrasonic imaging technology has been developing continuously, such as gray scale display and color display, real-time imaging, ultrasonic holography, penetrating ultrasonic imaging, ultrasonic computed tomography, three-dimensional imaging, intracavity ultrasonic imaging and so on.

Ultrasonic imaging method is often used to judge the position, size and shape of organs, determine the scope and physical properties of lesions, provide some anatomical maps of gland tissues, and distinguish normal and abnormal fetuses. Widely used in ophthalmology, obstetrics and gynecology, cardiovascular system, digestive system and urinary system. At present, ultrasonic imaging technology has also been applied in the field of traditional Chinese medicine, such as using Doppler flowmeter to detect the blood flow of various pulse conditions. So as to provide an index for objectification and quantification of pulse condition; Ultrasound imaging can also be used to study the objectification of TCM syndromes.

4 USG imaging basic principle and equipment 4. 1 Physical characteristics of ultrasonic wave is a kind of mechanical wave, which is generated by mechanical vibration of objects. It has physical quantities such as wavelength, frequency and propagation speed. The ultrasonic frequency used in medicine is 2.5 ~ 10 MHz, and the commonly used frequency is 2.5 ~ 5 MHz. Ultrasonic wave needs to propagate in media, and its speed is different in different media, the fastest in solid, the second in liquid and the slowest in gas. It is about 150m/s in human soft tissue. The medium has a certain acoustic impedance, which is equal to the product of the density of the medium and the ultrasonic velocity.

Ultrasonic waves propagate in a straight line in the medium and have good directivity, which is the basis of detecting human organs with ultrasonic waves. When the ultrasonic wave propagates through the interface of two adjacent media with different acoustic impedances, the acoustic impedance difference is greater than 0. 1%, and the interface is obviously larger than the wavelength, that is, the large interface, so that reflection occurs, part of the acoustic energy is refracted in the adjacent media behind the interface, the ultrasonic wave continues to propagate, and then it is reflected when it meets another interface until the acoustic energy is exhausted. The reflected ultrasonic wave is an echo. The greater the acoustic impedance difference, the stronger the reflection. If the interface is smaller than the wavelength, that is, the interface is small, scattering will occur. The propagation of ultrasonic waves in the medium will also be attenuated, that is, the amplitude and intensity will be reduced. Attenuation is proportional to the attenuation coefficient of the medium, inversely proportional to the square of the distance, and also related to the absorption and scattering of the medium. Ultrasound also has Doppler effect, and the movement of the moving interface relative to the sound source can change the echo rate. This effect enables ultrasound to detect heart activity, fetal activity and blood flow.

4.2 Basic principle of ultrasonic imaging The human body structure is a complex medium of ultrasound, and various organs and tissues, including pathological tissues, have their specific acoustic impedance (table 14 1) and attenuation characteristics. So it constitutes the difference of acoustic impedance and attenuation. When ultrasound is injected into the body, it will pass through organs and tissues with different acoustic impedance and attenuation characteristics from the surface to the deep, resulting in different reflections and attenuation. This different reflection and attenuation is the basis of ultrasonic images. According to the intensity of the echo, the received echo is displayed on the screen with different light spots in turn, and then the cross-sectional ultrasonic image of the human body can be displayed, which is called spectrogram or echo diagram.

Table 14 1 Sound Velocity and Acoustic Impedance of Different Media in Human Body

Dielectric density (g/cm3) Ultrasonic longitudinal wave velocity (m/s) Characteristic impedance (105R* Test frequency (MHz): air 0.00 1293 332 0.000429 2.9 water 0.99341523/kloc-0. Shang01615001.5241.0 Muscle1.0741.6841.0 Bone1.

The surface of the human organ is surrounded by a membrane, and the acoustic impedance difference between the membrane and the underlying tissue is large, forming a good interface reflection, and a complete and clear peripheral echo appears on the acoustic image, thus showing the outline of the organ. According to the surrounding echo, the shape and size of the organ can be judged.

Ultrasound passes through different normal organs or lesions, and its internal echo can be different degrees of non-echo, low echo or strong echo.

Anechoic: The area where ultrasound passes has no reflection and becomes anechoic dark area (shadow), which may be caused by the following situations: ① Liquid dark area: homogeneous liquid with little or no difference in acoustic impedance, which does not form a reflection interface and forms a liquid dark area, such as blood, bile, urine, amniotic fluid, etc. In this way, blood vessels, gallbladder, bladder and amniotic cavity are all dark areas of liquid. Pathological conditions, such as pleural effusion, pericardial effusion, ascites, pus, hydronephrosis, cystic tumor containing liquid, hydatid cyst, etc., also show as liquid dark area, which becomes a good sound transmission area. In dark areas, the echo usually increases and a bright band of light (white shadow) appears. ② Attenuated dark area: Tumors, such as large cancers, are obviously attenuated due to the absorption of ultrasound by tumors, and there is no echo, resulting in attenuated dark areas. (3) Substantial dark area: homogeneous substance with small acoustic impedance difference, and anechoic dark area can appear. Normal tissues such as renal parenchyma and spleen, pathological tissues such as renal carcinoma and vitreous degeneration can show dark areas of parenchyma.

Hypoechoic: The internal echoes of parenchymal organs, such as the liver, are evenly distributed punctate echoes. When acute inflammation occurs and exudation occurs, its acoustic impedance is less than that of normal tissue, and sound transmission increases, resulting in low echo area (gray shadow).

Strong echo: It can be strong echo, strong echo, strong echo. ① Strong echo: For tumors with dense tissues or increased blood vessels in the parenchymal organs, the acoustic impedance changes greatly, and the reflection interface increases, so that the local echo is enhanced, showing dense light spots or light masses (gray shadows), such as cancer, fibroids and hemangioma. ② Strong echo: The internal structure of the medium is dense, and there is obvious acoustic impedance difference with the adjacent soft tissue or liquid, which causes strong reflection. Such as bones, stones, calcification, strong echo areas (white shadows) may appear. Due to poor sound transmission, the acoustic energy below is attenuated, resulting in anechoic dark areas, that is, sound shadows. ③ Strong echo: Because the acoustic impedance of air-containing organs such as lung and inflatable gastrointestinal tract is very different from that of adjacent soft tissues, almost all acoustic energy is reflected back and cannot be transmitted, and a strong light band appears.

4.3 There are many kinds of ultrasound equipment in ultrasound equipment. In the early stage, amplitude modulation mode, namely A-mode ultrasound, was used to reflect the echo with amplitude change. Brightness mode, that is, B-ultrasound, uses different light spots to reflect echo changes, and displays images with 9-64 gray levels on the screen, with strong echoes lit and weak echoes dimmed.

According to different imaging methods, it can be divided into static imaging and dynamic imaging or real-time imaging. The former obtains static sonogram with wide display range and clear image, but it takes a long time to check and is seldom used. The latter can obtain multiple images (20 ~ 40 frames per second) in a short time, so it can observe the dynamic changes of organs, but the image display range is small and the image is slightly unclear.

Ultrasonic equipment is mainly composed of ultrasonic transducer, i.e. probe, transmitter and receiver, display and recording, and power supply (figure 14 1).

Figure 14 1 Schematic diagram of the basic structure of pulse echo ultrasonic equipment.

Transducer is an electro-acoustic transducer, which is composed of piezoelectric crystals and completes the generation of ultrasonic waves and the reception of echoes. Its performance affects sensitivity, resolution and artifact interference. B-ultrasound equipment is mostly pulse echo type. Multi-probes of electronic wire array perform square scanning, and probes of electronic phased array perform sector scanning (Figure 142). In order to guide puncture with the help of ultrasonic image, there is also a puncture probe

Figure 142 Real-time Scanning Probe

A. Electronic wire array B. Electronic phased array

The performance of the probe is divided into 3.0 MHz, 3.5 MHz and 5.8MHz. The larger the MHz, the smaller its permeability. Select the appropriate probe according to the detection site. For example, an 8MHz probe is used for eye scanning and a 3.0MHz probe is used for pelvic scanning. A ultrasound equipment can be equipped with several probes with different performances for alternate use.

Cathode ray tube for display, multi-frame camera and video recorder for recording.

The characteristic spectrogram of USG image reflects the existence and strength of echo with different gray levels between light (white) and dark (black). No echo is a dark area (black shadow), and strong echo is a bright area (white shadow).

The sonogram is a slice image. By changing the position of the probe, we can obtain acoustic images in any direction and observe the movement of the active organs. However, the range of image display is not as large and clear as X-ray, CT or MRI images.

6 USG inspection technology ultrasonic exploration mostly adopts supine position, but other positions such as lateral position can also be used. * * * Can be changed during the exploration process.

The direction of the tangent plane can be transverse, longitudinal or inclined.

Patients take appropriate * * *, expose the skin, apply coupling agent, and exhaust the air between the probe and the skin. The probe is close to the skin for scanning, and the image is observed during scanning. If necessary, freeze it, stop the frame, observe it carefully, make records, and take photos or videos.

Attention should be paid to the size, shape and surrounding echoes of organs, especially the back wall echo, internal echo, active state, the relationship between organs and neighboring organs and their activities.

7 USG image analysis and diagnosis When observing the sonogram, we should first know the orientation of the section in order to identify the anatomical structure involved. Pay attention to the peripheral echoes, including the marginal echoes of organs and large masses, so as to observe their size, shape, position and activity. Cursor can be used to measure its diameter, area or volume and judge whether it is increasing or decreasing. Whether there is local swelling; Have you changed gears, how to move and so on. It is necessary to observe the internal echoes of organs and large masses, including the intensity, quantity and distribution of echoes and the surrounding conditions of echoes (such as silent shadows). Because it can reflect the internal nature of organizational structure. Also pay attention to the changes of adjacent organs, including compression displacement or invasive injury. It is difficult to diagnose diffuse lesions according to the changes of organ size, shape and internal echo, but it is easier to find space-occupying lesions in organs by relying on localized internal echo anomalies.

The change of the sonogram obtained by comprehensive judgment. If it is a local lesion, determine the location of the lesion (for example, in which part of an organ); The size and number of lesions; The physical properties of the lesion are liquid, substance, gas or mixture; Pathological nature, inflammation or tumor, benign or malignant, primary or metastatic, cancer or sarcoma, etc.

Ultrasound images can easily find the focus, determine the location and size of the focus, and determine whether the focus is liquid, solid or gas-containing. Benign and malignant lesions can also be distinguished. For example, the peripheral echo of benign lesions is clear, the edge is smooth, the internal echo is uniform, and the attenuation is not obvious, while the peripheral echo of malignant lesions is unclear, the edge is not smooth, the outline is irregular, and the internal echo is uneven. Hemorrhagic and necrotic areas may have no echo, but the attenuation is also obvious.

The clinical application of USG diagnostic ultrasound is widely used in the examination of heart, abdomen and pelvic organs, including pregnancy. Such as liver cancer, hepatic hemangioma, liver abscess, liver cirrhosis, gallstones and tumors, pancreatic and splenic diseases and ascites; Examination of kidney, bladder, prostate, adrenal gland, uterus and ovary; Eye, thyroid and breast examination; It is of considerable value for the diagnosis of pregnancy, the location of fetal position and placenta, and the judgment of multiple births, stillbirths, fetal malformations and hydatidiform mole (Figure 143).

Figure 143 ultrasonic image

A. Normal uterus (↓) B. Ovarian dermoid cyst (↓) C. Pregnancy (↓) D. Fetal head aura (↓) E. Placenta previa (↓) F. Placenta previa (↓ uterine orifice) BL. Bladder UT Uterine cyst placenta AM. Amniotic fluid FA. embryo