What is Ultrasound Imaging?

Ultrasound (US) medicine is a combination of acoustics, medicine, optics and electronics. The application of acoustic technology above the audible sound frequency in the medical field is ultrasound medicine. It includes ultrasound diagnostics, ultrasound therapy, and biomedical ultrasound engineering. Therefore, ultrasound medicine has the characteristics of a combination of medicine, science, and work.

Ultrasound imaging uses an ultrasonic sound beam to scan the human body, and receives and processes reflected signals to obtain images of internal organs. There are many commonly used ultrasonic instruments: Type A (amplitude modulation type) indicates the strength of the reflected signal by the amplitude of the amplitude, and it displays an "echo map". M-type (spot scanning type) represents the spatial position from light to deep in the vertical direction and time in the horizontal direction, which is displayed as the movement curve of the light point at different times. The above two types are one-dimensional display, and the application range is limited. Type B (brightness modulation type) is an ultrasonic section imager, referred to as "B-ultrasound". The intensity of the received signal is represented by light points with different brightness. When the probe moves in the horizontal position, the light points on the display screen also move in the horizontal direction synchronously. For two-dimensional imaging. As for the D type, it is made according to the ultrasonic Doppler principle. Type C uses a television-like scanning method to display a cross-sectional acoustic image perpendicular to the sound beam. In recent years, ultrasound imaging technology has been continuously developed, such as gray-scale display and color display, real-time imaging, ultrasound holography, penetrating ultrasound imaging, ultrasound parallel tomography, three-dimensional imaging, and ultrasound imaging in the body cavity.

Ultrasound imaging methods are commonly used to determine the location, size, and shape of organs, determine the scope and physical properties of lesions, provide anatomical maps of some glandular tissues, identify normal and abnormal fetuses, and be used in ophthalmology, obstetrics and gynecology, and the cardiovascular system, The digestive system and urinary system are widely used.

Chinese name: Ultrasound imaging
Foreign name: Ultrasound

Short name: US
Solid: Combination of acoustic medical optics and electronics

The development of ultrasound imaging

Established in the 1950s, and widely used in the 1970s, ultrasound diagnostic technology is widely used. The general development trend is from static to dynamic images (rapid imaging), from black and white to color images, from two-dimensional to three-dimensional images, and from reflection. The normal transmission method is explored in order to obtain specific and specific ultrasound signals and achieve the purpose of quantification and specific diagnosis.

In the past 30 years, medical ultrasound diagnostic technology has made revolutionary leap after revolution. In the 1980s, interventional ultrasound gradually became popular. The application of body cavity probes and intraoperative probes expanded the scope of diagnosis and improved the diagnostic level. The application of internal ultrasound, three-dimensional imaging, and new acoustic contrast agents has taken ultrasound diagnosis to a new level. Its development speed is amazing, and it has become the first choice for clinical diagnosis of various diseases, and has become a very important series of diagnostic technology with multiple parameters.

Basic principles of ultrasound imaging

Ultrasound imaging sound wave

Waves that can cause sound perception in the auditory organ are called sound waves. The frequency range of sound waves that humans can sense is about 20-20000HZ. The sound waves with a frequency exceeding 20000HZ, which are not felt by the human sense organs, are called ultrasonic waves.

The basic physical properties of sound waves are as follows:

(A) the frequency, period and speed of sound waves

Sound source vibration produces sound waves. There are three types of sound waves: longitudinal wave, transverse wave and surface wave. The longitudinal wave is a kind of dense wave, just like a wave generated on a spring. Ultrasonic waves used for human diagnosis are longitudinal waves generated in the elastic medium by sound source vibration. Sound waves propagate in the medium, and the particles in the medium vibrate back and forth once at the equilibrium position to complete a full vibration. The time required for a full vibration is called the vibration period (T). The number of full vibrations per unit time is called frequency (f), and the unit of frequency is hertz (HZ). f = 1 / T, the sound wave propagates at a certain speed in the medium, the particle vibrates for a week, and the wave advances by one wavelength (). Wave speed (C) = / T or C = f · .

(Two) acoustic impedance

Sound waves propagate through the medium, and their propagation speed is related to the density of the medium. The speed of sound is faster in denser media than in less dense media. The velocity of sound is faster in a medium with greater elasticity than in a medium with less elasticity. This leads to the definition of acoustic impedance, which is the product of the density of the medium () and the speed of sound (C). It is represented by the letter Z, and Z = · C.

Ultrasound imaging ultrasound

Ultrasound is a sound wave with a frequency greater than 20KHZ, which is invisible to the human ear. It is also a longitudinal wave, which can propagate in solids, liquids and gases, and has the same physical properties as sound waves. But because of its high frequency and short wavelength, it also has some characteristics.

Ultrasound imaging beam

Ultrasound is beam-emitting. This point is different from ordinary sound waves, but similar to the nature of light, it can be concentrated to propagate in one direction and has strong directivity. The ultrasonic waves emitted by the transducer have a narrow cylindrical distribution, so they are called ultrasonic beams.

Ultrasound imaging reflection and refraction

When a beam of ultrasound is incident on the interface of two media that is many times larger than its own wavelength, reflection and refraction occur. Reflection follows the law of reflection, and refraction follows the law of refraction. Because the angle of incidence is equal to the angle of reflection, ultrasonic sound detection requires that the sound beam be as perpendicular to the tissue interface as possible. The reflection of ultrasonic waves is also related to the acoustic impedance on both sides of the interface. The larger the difference between the acoustic impedances of the two media, the stronger the reflection of the incident ultrasonic beam. The smaller the acoustic impedance difference, the weaker the reflection.

The transmitted sound passing through the large interface may continue in the direction of the incident sound beam, or it may propagate away from the direction of the incident sound beam. The latter phenomenon, called ultrasonic refraction, is caused by the difference in sound velocity in the two media.

Ultrasound imaging scattering and diffraction

During the propagation of ultrasonic waves in the medium, if the diameter of the interface of the object encountered is larger than the wavelength of the ultrasonic wave, reflection occurs. If the diameter is smaller than the wavelength, the propagation direction of the ultrasonic wave will deviate, and it will propagate in the original direction after bypassing the object. There are very few reflected echoes at this time. This phenomenon is called diffraction. Therefore, the shorter the wavelength, the better the resolution of the ultrasound. If the diameter of the object is much smaller than the long particles of ultrasonic waves, most of the ultrasonic waves continue to propagate forward when passing through such particles, and a small part of the ultrasonic energy is radiated by the particles in all directions. This phenomenon is called scattering.

Ultrasound imaging ultrasound attenuation

When ultrasonic waves propagate in a medium, the incident ultrasonic energy gradually decreases with the increase of the propagation distance. This phenomenon is called attenuation of ultrasonic waves.

There are two reasons for attenuation: (1) when ultrasonic wave propagates in the medium, the sound energy is converted into thermal energy, which is called absorption; (2) the reflection and scattering of the ultrasonic wave by the medium causes the energy of the incident ultrasonic wave to be transferred in other directions and returned. Ultrasonic energy is getting smaller and smaller.

Basic ultrasound imaging equipment

Doppler ultrasound

Fundamental

Doppler effect

The Doppler effect was first proposed by Austrian physicist Kristin John Doppler in 1842. Describes the phenomenon that the light wave frequency increases or decreases when the light source and the receiver move relative to each other. The difference between the received and transmitted frequencies caused by this relative motion is called the Doppler shift or the Doppler effect.

Acoustic waves also have the characteristics of the Doppler effect. Doppler ultrasound is most suitable for detecting moving fluids, so Doppler ultrasound is particularly important for detecting blood flow in the heart and large blood vessels.

The basic way of Doppler echocardiography

1 Pulsed Doppler (PW)

2 Continuous Doppler (CW)

3 color Doppler flow imaging (CDFI)

Ultrasound imaging ultrasound system

(A) Type A ultrasound diagnostic instrument

A-ultrasound is an amplitude modulation type, which is the most popular and basic type of ultrasound diagnostic instrument in the early days of China, and has been basically eliminated.

(Two) M-type ultrasound diagnostic instrument

M-ultrasound uses brightness modulation to reflect the strength of the echo with brightness. M-type shows the curve of the distance of each layer of tissue in the body to the surface (probe) over time. It reflects the one-dimensional spatial structure. Detecting the heart, so often called M-mode echocardiography, is currently set on the instrument as a display mode of a two-dimensional color Doppler echocardiograph.

(Three) type B ultrasound diagnostic instrument

The B-type display is developed using A-type and M-type display technology. It changes the A-type amplitude modulation display to the luminance modulation display. The brightness changes with the size of the echo signal, and reflects the two-dimensional tomographic image of human tissue.

The real-time section image displayed by type B has strong authenticity, good intuitiveness, and easy to grasp. It has only a history of more than 20 years, but it has developed very quickly, and the instrument has been continuously updated. In recent years, new and improved B-type instruments have appeared every year. The B-type instrument has become the most basic and important device for ultrasound diagnosis. At present, the more commonly used B-mode ultrasound imaging methods are: scanning methods: linear (linear) scanning, fan scanning, trapezoidal scanning, arc scanning, radial scanning, circumferential scanning, composite scanning; Scanning drive methods: manual scan, mechanical scan, electronic scan, composite scan.

(D) D-type ultrasound diagnostic instrument

Ultrasound Doppler diagnostic instrument is referred to as D-type ultrasound diagnostic instrument. This type of instrument uses the principle of Doppler effect to detect moving organs and blood flow. It is essential in the diagnosis of cardiovascular diseases. Currently, ultrasound systems used for cardiovascular diagnosis are equipped with Doppler, pulsed Doppler and continuous Doppler. In recent years, many new topics cannot be separated from the Doppler principle, such as the detection of blood supply in the peripheral blood vessels, blood vessels of the internal organs of the human body, and the neoplastic tumors.

(V) Color Doppler blood flow imaging device

Color Doppler flow imaging is referred to as color Doppler ultrasound, which includes two-dimensional section imaging and color imaging. High-quality color display requires satisfactory black and white structure imaging and clear color blood flow imaging. On the basis of displaying the two-dimensional slice, turn on the "color blood flow imaging" switch, and the color blood flow signal will be automatically superimposed on the black and white two-dimensional structure display. Speed display, variance display or power display can be selected as required. At present, there are many types and types of color ultrasound in the international market, and the development of grades is changing with each passing day. It is also characterized by high information volume, high resolution, high automation, wide range, simplicity and practicality.

Ultrasound imaging image features

Different types of ultrasound systems have different image characteristics. Since B-mode ultrasound is the most important diagnostic method, the image characteristics are described below:

Echo description of the ultrasound imaging slice image

1 Description of echo strength: According to different gray levels in the image, the echo signal is divided into strong echo, iso-echo, low echo and no echo. The standard of echo strength or level is generally determined by comparing the normal echo of the organ or comparing the echo intensity of the lesion with the surrounding normal organ echo. If the liquid is non-echo, stone gas or calcification is strong echo. The internal echo of normal human soft tissues is arranged from strong to weak as follows: renal sinus> placenta> pancreas> liver> spleen> renal cortex> subcutaneous fat> renal medulla> brain> venous blood> bile and urine.

2 Description of the echo distribution: According to the distribution of light points in the image, it is divided into uniform or uneven, dense or sparse. The echo distribution in the lesion can be expressed as "homogeneous" or "non-uniform".

3 Description of the echo form: light clusters: Echo light spots are clustered in bright clusters with a certain boundary. Light spot: Echo light spots are clustered in bright small pieces with clear boundaries. Light Dots: The echoes are tiny dots. Halo: Displays a circular or circular-like echo ring. Light band: Displays band-like echoes.

4 Description of some special signs: Namely visualize some lesions sonograms as certain signs to emphasize these signs. Commonly used are "target ring" sign, "bull's eye" sign, "hump sign", " "Double barrel gun" sign and so on.

5 Color Doppler blood flow imaging can also display multiple parameters such as the distribution, orientation, size, thickness, morphology, and blood flow velocity of blood vessels in the organs or inside, outside, and peripheral blood vessels.

Common artifacts in ultrasound imaging

1 multiple reflections

Ultrasound is irradiated vertically to a flat interface and the sound waves are reflected back and forth between the probe and the interface. Multiple echoes of equal distance appear, and the intensity gradually decreases, especially on the interface formed by thin layers of gas, such as the left liver lobe and gas in the stomach. A small echo between the bladder echoes and the anterior part.

2 multiple internal reverberations

Ultrasound is reflected back and forth within the target, forming comet tail signs, such as intrauterine birth control rings.

3 Slice thickness artifacts are also called partial volume effects.

It is caused by the wide sound beam width (that is, the slice thickness of the ultrasound cut plane is thicker). Such as pseudobile mud-like images in the gallbladder.

4 sidelobe artifacts

It is caused by the side lobe reflection outside the main lobe of the sound beam, and presents "dog ear" -like or "veiled" -like images on both sides of strong echoes such as stones and intestinal qi.

5 Audiovisual

Due to the strong reflection in the front or the existence of a material with great sound attenuation, the area behind the sound beam that cannot be reached by the sound beam is called the echoless zone. The acoustic shadow can be used to identify stones, calcifications, bones, etc. .

6 refracted sound and shadow

Ultrasound enters high-sonic-velocity media from low-velocity-velocity media. When the angle of incidence exceeds the critical angle, total reflection occurs, so that sound shadows appear behind it. They are seen on both sides of the spherical structure or on the edges of both sides of the organ.

7 specular artifacts

When an ultrasound beam is projected on a large human echo interface with a smooth surface, such as a transverse plane, as if the light is projected on a plane mirror, it produces similar real and virtual images, such as two symmetrical mass echoes on both sides of the transverse plane.

Ultrasound imaging

Ultrasound imaging device

1 Real-time linear array ultrasound diagnostic instrument: suitable for general abdominal examination, there can be many different frequency probes. The main disadvantage is that the probe has a large contact surface with the human body, and a large sound transmission window is needed for the sound beam to effectively pass through the inspection target during inspection.

2 Real-time fan-type ultrasound diagnostic apparatus: Cardiac probing is most commonly used, and the probe is small, which is convenient for intercostal scanning. The disadvantage is that the near-field visual field is small.

3 Real-time convex array ultrasound diagnostic instrument: The convex array probe has the advantages of a larger field of view in the near field than a fan-type probe and a wider field of view in the far field than a linear array probe.

4 Color and Spectrum Doppler Ultrasound Diagnostic Apparatus: It is used to explore the hemodynamic changes such as blood flow velocity, blood flow of blood vessels, peripheral blood vessels, and blood vessels related to various organs and lesions.

Preparation before ultrasound imaging detection

It is generally not necessary to prepare before detection. When detecting deep organs that are susceptible to gas interference from the digestive tract, fasting inspection or more stringent intestinal preparation is required. The gallbladder examination requires a light diet the night before and no breakfast on the day; obstetrics and gynecology and bladder prostate examinations require filling the bladder; bowel movements or enema before rectal examinations; some special examinations have special preparation requirements before examinations, which will be detailed in specific chapters Intro.

Ultrasound imaging detection method and position

(A) detection method

1 Direct detection method: The probe is in direct contact with the skin or mucous membrane of the subject, which is a conventional detection method.

2 Indirect detection method: Injecting liquid between the probe and the human body or inserting a water sac, Proxon coupling (delay) block, etc., makes the ultrasound have a time delay from transmitting to entering the human body. The purpose is threefold: to make the tested part fall into the gathering area and increase the resolution; to couple the uneven parts on the surface; to protect the delicate test tissue (such as cornea) from abrasions.

(Two) position

The position of ultrasound detection is different due to different detection positions, and various positions can be used, such as supine position, left and right lateral position, prone position, sitting position, standing position, lithotomy position, knee and chest position, etc., without certain restrictions. Will be introduced in each monograph.

Ultrasound imaging diagnosis and clinical application

B Clinical application of ultrasound imaging B-mode ultrasound detection technology

Ultrasound diagnosis is based on detailed observation and analysis. Capturing various characteristics, comprehensively analyzing the cause, studying changes in various physiological conditions, and combining other forms of diagnosis.

(A) ultrasound image observation

1 Organ shape and size, flexibility or mobility Various organs have their natural anatomy and size. Observe the outline of the organs for morphological abnormalities, the shape, location, size, number, range, etc. of the mass, and the degree of movement of the abdominal organs.

2 Edge echo of the lesion After the lesion is found, observe the edge echo of the lesion, whether it is enveloped, whether it is smooth, the thickness of the wall, and whether there are halos in the periphery.

3 Echoes of the back wall and the back Due to different absorption and attenuation of sound energy by various normal tissues and diseased tissues of the human body, different echoes at the back are exhibited. If liquid cysts or abscesses appear, the posterior wall echoes "enhance"; while calcification, stones, gas, etc., form "sound shadows" behind them. Some homogeneous parenchymal lesions that closely resemble fluid lesions have no echo-enhancing effect at the rear.

4 The internal structural characteristics can be divided into the normal structure, the normal structure disappears, the interface increases or decreases, the size and uniformity of the interface scattering points are different, and various other types of abnormal echoes.

5 Peripheral relationship Determine the continuity of the lesion and the surrounding organs according to the local anatomical relationship, with or without compression, adhesion or infiltration.

6 Functional testing, such as the use of fat meal test to observe the contractile function of the gallbladder. After drinking on an empty stomach, the emptying function of the stomach and the state of contraction and peristalsis were measured.

(B) common pathological image features

1 Cystic and parenchymal lesions

Ultrasound has a significant image difference between liquid and parenchyma, so it is easy to distinguish.

2 Homogeneous and heterogeneous lesions

Homogeneous lesions have uniform low echo, isoechoic or strong echo, while heterogeneous lesions have complex echo structure.

3 Calcified and gaseous lesions

The image of calcified lesions is stable, the sound and shadow are clear, the image of gaseous lesions is unstable, and the sound and shadow are muddy.

4 Inflammatory and fibrotic lesions

In the early stage of acute inflammation, edema is predominant, local echo is reduced, organs are swollen, and meridian values are increased. Chronic inflammatory fibrous tissue is increased, and echoes are enlarged.

Fibrotic lesions are mostly echogenic and behave differently depending on the extent of the lesion. Such as schistosomiasis liver fibrosis is a typical "map" -like changes.

5 Benign and malignant lesions

Generally speaking, benign lesions have a uniform texture and a single interface, so the echoes are uniform and regular. Malignant lesions are characterized by rapid growth, accompanied by bleeding, degeneration, and complex and uneven tissue interface in the tumor, showing irregular echo structure.

Such as (1) tumor edge: Yes: benign or malignant does not stretch outward; False edge: halo, buffalo eyes; rules: benign and malignant; clear boundaries: more benign; Pseudofoot extension: Malignant as much.

(2) Internal echo: uniform: benign; uneven: greater malignant.

(3) Other internal structures: Normal: mostly benign; Abnormal: mostly malignant.

(4) Rear echo: normal or enhanced: mostly benign; normal or weakened: mostly malignant.

(5) Invasion or metastasis: Blockage or invasion of ducts, proliferation or metastasis of nearby tissues and / or organs are considered malignant.

Clinical application of ultrasound imaging ultrasound Doppler detection technology

Ultrasound Doppler is a detection technology that has been rapidly developed in recent years. With the advancement of electronics, this method has become increasingly widely used in clinical practice. It is used for the perfusion of parenchymal organs and small organ blood in heart diseases and peripheral vascular diseases. Examination of the flow supply, blood supply of space-occupying lesions, and fetal blood circulation are of great value.

(I) Identify the nature of the liquid dark area

There are various forms of liquid dark areas on the ultrasound image of the cut plane, which can represent pus cavity, effusion, bile, urine, amniotic fluid, or blood, etc. Generally, according to the anatomical part, the surrounding contour, and the length of the line And continuous relationships, etc., whose properties are easy to distinguish, but sometimes because of complex sections and many dark areas, it is difficult to identify. There are obvious differences in arterial, venous, and stationary fluid lumens when Doppler examinations are performed, which is of great help in identifying the nature. For example, when the intrahepatic bile duct is highly dilated, it is difficult to distinguish the portal vein from the dilated bile duct in a certain section. Color blood flow imaging is added. The portal vein has a color blood flow display and a typical portal vein spectrum, but the bile duct has no blood flow display. Another example is the diagnosis of deep venous thrombosis of the lower extremity. First, use color Doppler to identify which two blood vessels are arteries and which are veins, and then follow up further.

(B) identify the blood supply of organs and diseased tissues

Color Doppler blood flow imaging and energy map can clearly show the normal blood supply of the organs. When there are lesions or neonatal occupying lesions, the blood flow display can make important differential diagnosis. Patients with hyperthyroidism have abnormally abundant thyroid blood supply, which is a typical feature of the "fire sea" sign; liver tumors, such as primary liver cancer, can detect the rich blood supply inside and around the tumor, and see the arterial spectrum; such as hemangiomas, there is little blood flow. No arterial spectrum.

(3) Detection of blood flow velocity

The blood flow velocity of any blood vessel and heart valve mouth in the human body has a certain normal range. For example, the peak velocity of the mitral valve diastolic phase is 60cm / s 130cm / s, and the peak velocity of the right main branch of the portal vein is about 18cm / s. The blood flow velocity parameters include peak velocity, acceleration, deceleration, average velocity, velocity integral, etc. The above parameters can be used to judge the abnormal hemodynamics.

(IV) Estimated pressure difference

Using mathematical formula-simplified Bernoulli's equation: P1-P2 = 4V2 (P1, P2 respectively represent the pressure before and after the measured valve orifice, and V is the blood flow velocity when passing through the valve orifice), the pressure before and after the valve orifice can be measured Poor, indirectly reflects whether the blood flow is unobstructed and whether there is stenosis, and the pulmonary artery pressure can be estimated by measuring the tricuspid regurgitation velocity.

(E) Measuring blood flow

When blood flows through a lumen, its blood flow (Q) is closely related to the speed of blood flow (V), the size of the lumen area (A), and the length of the blood flow time (T). Q = V · A · T . According to the above formula, most color Doppler blood flow imaging devices can automatically calculate blood flow after tracing the outline of the blood flow spectrum and marking the positions of the two side walls of the lumen, which is of great clinical help.

The principle of ultrasound imaging

Array sound field delayed superimposition imaging is the most traditional, simplest, and most widely used imaging method in practice. In this way, different delays are introduced to each unit of the array, and then they are combined into a focused beam to achieve imaging of each point of the sound field.