Ultrasound examination or ultrasound (echosopy, sonography), like computed tomography or nuclear magnetic resonance imaging, belongs to modern visual research methods. However, there are other ultrasound methods that can be used to examine the baby's blood vessels or heart sounds.

Ultrasound can be used to record movements. Only the frequency of the sent sound waves must exceed the limit of the flicker frequency perceived by the eye. This technique is used, for example, to assess fetal movements in the womb.

Visual ultrasound examinations

Ultrasound is a method based on echolocation; pulsed ultrasound waves are used for diagnostic purposes. The main part of the ultrasonic device is a special ultrasonic sensor containing a piezoelectric crystal - a source and receiver of ultrasonic waves, capable of transforming electric current into sound waves and vice versa, turning sound waves back into electrical impulses. It sends sound waves at short intervals in the direction of the organ being examined, from which the sound waves return as an echo. This echo is captured by the sensor and transformed into electrical impulses; the connected computer converts them into luminous points of varying intensity (the stronger the echo, the brighter the point), from which an image of the organ or pathological process being studied is obtained on the monitor screen. If necessary, photographs are taken and attached to the medical history. During an ultrasound, a special sensor is applied to the body in certain places.

Non-visual ultrasound examinations

The basis of ultrasound examination (without obtaining an image) is the Doppler effect - a change in the frequency of sound when reflected from a moving object. In biological media, such an object is blood inside the vessels. Thus, the sound wave is reflected by the formed elements of the blood, and it returns back. The reflected sound waves are superimposed, resulting in tones of sound being heard. The pitch of the tone can be used to judge the speed of blood flow. This type of ultrasound examination is most often used to determine the tones of the fetus during pregnancy, to monitor these tones during treatment and to diagnose various diseases of the blood vessels.

Performing an ultrasound

The ultrasound technique is simple. The study is not difficult to carry out; you just need to attach a special ultrasound sensor to the patient’s body. For better contact of the sensor with the surface of the body, the patient’s skin is lubricated with a special gel.

Diagnosis using ultrasound

To perform a high-quality ultrasound, you need a good “conductor” for the unhindered propagation of sound waves. Ultrasound is well suited for examining organs that contain water. Due to the fact that air is a poor conductor, ultrasound is difficult to perform with bloating. Sounds also travel poorly in bone tissue, so, for example, the skull can only be examined in small children whose fontanelles have not yet become overgrown.

When performing an ultrasound, the liver and gall bladder are clearly visible. On the monitor you can see not only a stone located in the gall bladder or a slowdown in the outflow of bile, but also changes in liver tissue, for example, one can assume the presence of fatty liver, cirrhosis or malignant tumors. Thanks to ultrasound, the kidneys and spleen are clearly visible. In the pelvis you can examine the prostate gland in men, the uterus and ovaries in women. In gynecology, vaginal echoscopy is increasingly being used, with which one can better assess the condition of a woman’s internal genital organs. When using an ultrasound examination, it is possible to examine the blood vessels of the patient's abdominal cavity and pancreas.

Is ultrasound dangerous?

Ultrasound examinations are completely safe. They do not use ionizing radiation, unlike, for example, radiography. Sonography is used even during pregnancy.

Ultrasound examination (sonography) is one of the most modern, informative and accessible methods of instrumental diagnostics. The undoubted advantage of ultrasound is its non-invasiveness, i.e. during the examination there is no damaging mechanical effect on the skin and other tissues. The diagnosis is not associated with pain or other unpleasant sensations for the patient. Unlike the widespread method, ultrasound does not use radiation hazardous to the body.

Operating principle and physical basis

Sonography makes it possible to detect the slightest changes in organs and catch the disease at a stage when clinical symptoms have not yet developed. As a result, a patient who undergoes an ultrasound in a timely manner increases the chances of a complete recovery.

Please note: The first successful studies of patients using ultrasound were carried out in the mid-fifties of the last century. Previously, this principle was used in military sonars to detect underwater objects.

To study internal organs, ultrahigh-frequency sound waves - ultrasound - are used. Since the “picture” is displayed on the screen in real time, this makes it possible to monitor a number of dynamic processes occurring in the body, in particular, the movement of blood in the vessels.

From a physics point of view, ultrasound is based on the piezoelectric effect. Quartz or barium titanate single crystals are used as piezoelements, which alternately work as a signal transmitter and receiver. When exposed to high-frequency sound vibrations, charges arise on the surface, and when current is applied to the crystals, mechanical vibrations are generated, accompanied by ultrasound radiation. The fluctuations are caused by a rapid change in the shape of single crystals.

Piezoelectric elements-transducers are a basic component of diagnostic devices. They represent the basis of sensors, which, in addition to crystals, contain a special sound-absorbing wave filter and an acoustic lens for focusing the device on the desired wave.

Important:The basic characteristic of the medium under study is its acoustic impedance, i.e., the degree of resistance to ultrasound.

As the wave beam reaches the boundary of zones with different impedances, it changes greatly. Some of the waves continue to move in the previously determined direction, and some are reflected. The reflection coefficient depends on the difference in the resistance of two neighboring media. The absolute reflector is the area bordering the human body and the air. 99.9% of the waves travel in the opposite direction from this interface.

When studying blood flow, a more modern and in-depth technique is used, based on the Doppler effect. The effect is based on the fact that when the receiver and the medium move relative to each other, the frequency of the signal changes. The combination of signals emanating from the device and reflected signals creates beats, which are heard using acoustic speakers. Doppler study makes it possible to determine the speed of movement of the boundaries of zones of different densities, i.e., in this case, to determine the speed of movement of liquid (blood). The technique is practically irreplaceable for an objective assessment of the state of the patient’s circulatory system.

All images are transmitted from the sensors to the monitor. The resulting image in the mode can be recorded on digital media or printed on a printer for a more detailed study.

Study of individual organs

A type of ultrasound called echocardiography is used to study the heart and blood vessels. In combination with assessing the state of blood flow through Doppler sonography, the technique makes it possible to identify changes in the heart valves, determine the size of the ventricles and atria, as well as pathological changes in the thickness and structure of the myocardium (heart muscle). During the diagnosis, sections of the coronary arteries can also be examined.

The level of narrowing of the lumen of blood vessels can be determined by continuous wave Dopplerography.

Pumping function is assessed using pulsed Doppler.

Regurgitation (the movement of blood through the valves in the opposite direction than normal) can be detected using color Doppler mapping.

Echocardiography helps diagnose serious pathologies such as latent forms of rheumatism and coronary artery disease, as well as identify neoplasms. There are no contraindications to this diagnostic procedure. If you have diagnosed chronic pathologies of the cardiovascular system, it is advisable to undergo echocardiography at least once a year.

Ultrasound of the abdominal organs

Abdominal ultrasound is used to assess the condition of the liver, gallbladder, spleen, great vessels (in particular the abdominal aorta) and kidneys.

Please note: For ultrasound of the abdominal cavity and pelvis, the optimal frequency is in the range from 2.5 to 3.5 MHz.

Kidney ultrasound

Ultrasound of the kidneys can detect cystic neoplasms, dilation of the renal pelvis and the presence of stones (). This kidney study must be carried out when.

Ultrasound of the thyroid gland

Ultrasound of the thyroid gland is indicated for this organ and the appearance of nodular neoplasms, as well as if there is discomfort or pain in the neck. This study is mandatory for all residents of environmentally disadvantaged areas and regions, as well as regions where the level of iodine in drinking water is low.

Ultrasound of the pelvic organs

A pelvic ultrasound is necessary to assess the condition of the organs of the female reproductive system (uterus and ovaries). Diagnostics allows, among other things, to detect pregnancy in the early stages. In men, the method makes it possible to identify pathological changes in the prostate gland.

Ultrasound of the mammary glands

Ultrasound of the mammary glands is used to determine the nature of neoplasms in the breast area.

Please note:To ensure the tightest possible contact of the sensor with the body surface, a special gel is applied to the patient’s skin before the start of the study, which, in particular, includes styrene compounds and glycerin.

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Ultrasound scanning is currently widely used in obstetrics and perinatal diagnostics, i.e., for examining the fetus at different stages of pregnancy. It allows you to identify the presence of pathologies in the development of the unborn child.

Important:During pregnancy, routine ultrasound examinations are strongly recommended at least three times. The optimal periods during which the maximum useful information can be obtained are 10-12, 20-24 and 32-37 weeks.

An obstetrician-gynecologist can detect the following developmental anomalies using an ultrasound:

• cleft palate (“cleft palate”);
• malnutrition (underdevelopment of the fetus);
• polyhydramnios and oligohydramnios (abnormal volume of amniotic fluid);
• placenta previa.

Important:in some cases, the study reveals the threat of miscarriage. This makes it possible to promptly place a woman in a hospital “for preservation”, giving the opportunity to safely carry the baby.

It is quite problematic to do without ultrasound when diagnosing multiple pregnancies and determining the position of the fetus.

According to a report by the World Health Organization, the preparation of which used data obtained in leading clinics in the world over many years, ultrasound is considered an absolutely safe research method for the patient.

Please note: ultrasonic waves, indistinguishable to the human hearing organs, are not something alien. They are present even in the noise of the sea and wind, and for some species of animals they are the only means of communication.

Contrary to the fears of many expectant mothers, ultrasound waves do not harm even the child during intrauterine development, that is, ultrasound during pregnancy is not dangerous. However, to use this diagnostic procedure there must be certain indications.

Ultrasound examination using 3D and 4D technologies

A standard ultrasound examination is carried out in two-dimensional mode (2D), that is, the monitor displays an image of the organ under study in only two planes (relatively speaking, you can see the length and width). Modern technologies have made it possible to add depth, i.e. third dimension. Thanks to this, a three-dimensional (3D) image of the object under study is obtained.

Equipment for three-dimensional ultrasound provides a color image, which is important when diagnosing certain pathologies. The power and intensity of ultrasound is the same as that of conventional 2D devices, so there is no risk to the patient’s health. In fact, the only disadvantage of 3D ultrasound is that the standard procedure takes not 10-15 minutes, but up to 50.

3D ultrasound is now most widely used to examine the fetus in the womb. Many parents want to look at the baby’s face even before his birth, but only a specialist can see anything in an ordinary two-dimensional black and white picture.

But examining a child’s face cannot be considered an ordinary whim; The three-dimensional image makes it possible to distinguish structural anomalies of the maxillofacial region of the fetus, which often indicate severe (including genetically determined) diseases. Data obtained from ultrasound, in some cases, can become one of the grounds for making a decision to terminate a pregnancy.

Important:It must be taken into account that even a three-dimensional image will not provide useful information if the child turns his back to the sensor.

Unfortunately, so far only a conventional two-dimensional ultrasound can provide a specialist with the necessary information about the state of the internal organs of the embryo, so a 3D study can only be considered as an additional diagnostic method.

The most “advanced” technology is 4D ultrasound. Now time has been added to the three spatial dimensions. Thanks to this, it is possible to obtain a three-dimensional image in dynamics, which allows, for example, to look at the change in facial expressions of an unborn child.

In 1794, Spallanzani noticed that if a bat's ears are plugged, it loses orientation, and he suggested that orientation in space is carried out through emitted and perceived invisible rays.

Ultrasound was first obtained in laboratory conditions in 1830 by the Curie brothers. After the Second World War, Holmes, based on the principle of a sonar device used in the submarine fleet, designed diagnostic units that became widespread in obstetrics, neurology and ophthalmology. Subsequent improvements in ultrasound equipment have led to the fact that this method has now become the most common for visualizing parenchymal organs. The diagnostic procedure is short, painless and can be repeated many times, which allows monitoring the treatment process.

What does ultrasound determine?

Ultrasonic method designed for remote determination of the position, shape, size, structure and movement of organs and tissues of the body, as well as for identifying pathological foci using ultrasound radiation.

Ultrasonic waves are mechanical, longitudinal vibrations environment, with an oscillation frequency above 20 kHz.

Unlike electromagnetic waves (light, radio waves, etc.), the propagation of ultrasonic sound requires a medium - air, liquid, tissue (it does not propagate in a vacuum).

Like all waves, V-sound is characterized by the following parameters:

• Frequency is the number of complete oscillations (cycles) over a period of time of 1 second. Units of measurement are hertz, kilohertz, megahertz (Hz, kHz, MHz). One hertz is an oscillation of 1 second.
• Wavelength is the length that one vibration occupies in space. Measured in meters, cm, mm, etc.
• The period is the time required to obtain one complete cycle of oscillations (seconds, milliseconds, microseconds).
• Amplitude (intensity - wave height) - determines the energy state.
• Velocity is the speed at which a Y wave travels through a medium.

Frequency, period, amplitude and intensity are determined by the sound source, and the speed of propagation is determined by the medium.

The speed of ultrasound propagation is determined by the density of the medium. For example, in air the speed is 343 m per second, in the lungs - more than 400, in water - 1480, in soft tissues and parenchymal organs from 1540 to 1620, and in bone tissue ultrasound moves more than 2500 m per second.

The average speed of ultrasound propagation in human tissue is 1540 m/s - most ultrasound diagnostic devices are programmed for this speed.

The basis of the method is the interaction of ultrasound with human tissue, which consists of two components:

The first is the emission of short ultrasonic pulses directed into the tissues being studied;

The second is image formation based on signals reflected by tissues.

Piezoelectric effect

To obtain ultrasound, special converters are used - sensors or transducers, which convert electrical energy into ultrasound energy. Receiving ultrasound is based on reverse piezoelectric effect. The essence of the effect is that when electrical voltage is applied to the piezoelectric element, its shape changes. In the absence of electric current, the piezoelectric element returns to its original shape, and when the polarity changes, the shape will again change, but in the opposite direction. If alternating current is applied to the piezoelectric element, the element will begin to oscillate at a high frequency, generating ultrasonic waves.

When passing through any medium, there will be a weakening of the ultrasonic signal, which is called impedance (due to the absorption of energy by the medium). Its value depends on the density of the medium and the speed of propagation of ultrasound in it. Having reached the boundary of two media with different impedances, the following changes occur: part of the ultrasonic waves is reflected and follows back towards the sensor, and part continues to propagate further; the higher the impedance, the more ultrasonic waves are reflected. The reflection coefficient also depends on the angle of incidence of the waves - a right angle gives the greatest reflection.

(at the interface between air and soft tissue, almost complete reflection of ultrasound occurs, and therefore, to improve the conduction of ultrasound in the tissue of the human body, connecting media - gel - are used).

The returning signals cause the piezoelectric element to oscillate and are converted into electrical signals - direct piezoelectric effect.

Ultrasonic sensors use artificial piezoelectrics such as lead zirconate or lead titanate. They are complex devices and, depending on the method of image scanning, are divided into sensors for devices slow scans are usually single-element and fast real-time scanning - mechanical (multi-element) and electronic. Depending on the shape of the resulting image, there are sector, linear and convex (convex) sensors In addition, there are intracavitary (transesophageal, transvaginal, transrectal, laparoscopic and intraluminal) sensors.

Advantages of fast scanning devices: the ability to evaluate the movements of organs and structures in real time, a significant reduction in the time for conducting research.

Advantages of sector scanning:

• large viewing area at depth, allowing you to cover the entire organ, for example, a kidney or a fetus;
• the ability to scan through small “transparency windows” for ultrasound, for example, in the intercostal space when scanning the heart, when examining the female genital organs.

Disadvantages of sector scanning:

• the presence of a “dead zone” of 3-4 cm from the surface of the body.

Advantages of linear scanning:

• a slight “dead zone”, which makes it possible to examine near-surface organs;
• the presence of several foci along the entire length of the beam (the so-called dynamic focusing), which ensures high clarity and resolution over the entire scanning depth.

Disadvantages of linear scanning:

• a narrower field of view at depth compared to sector scanning, which does not allow you to “see” the entire organ at once;
• inability to scan the heart and difficulty scanning the female genital organs.

Based on their operating principle, ultrasonic sensors are divided into two groups:

• Pulse echo – for determining anatomical structures, their visualization and measurement.
• Doppler - allow you to obtain a kinematic characteristic (assessment of the speed of blood flow in the vessels and heart).

This ability is based on the Doppler effect - a change in the frequency of received sound as blood moves relative to the wall of the vessel. In this case, the sound waves emitted in the direction of movement are compressed, as it were, increasing the frequency of the sound. Waves emitted in the opposite direction seem to stretch, causing a decrease in the frequency of sound. Comparing the original ultrasound frequency with the changed one makes it possible to determine the Doppler shift and calculate the speed of blood movement in the lumen of the vessel.

Thus, the ultrasonic wave pulse generated by the sensor propagates through the tissue and, upon reaching the border of tissues with different densities, is reflected towards the transducer. The received electrical signals are sent to a high-frequency amplifier, processed in the electronic unit and displayed as:

• one-dimensional (in the form of a curve) - in the form of peaks on a straight line, which allows you to estimate the distance between tissue layers, for example in ophthalmology (A-method “amplitude”), or to study moving objects, for example, the heart (M-method).
• two-dimensional (B-method, in the form of a picture) image, which allows you to visualize various parenchymal organs and the cardiovascular system.

To obtain an image in ultrasound diagnostics, ultrasound is used, which is emitted by a transducer in the form of short ultrasonic pulses (pulse).

Additional parameters are used to characterize pulsed ultrasound:

• The pulse repetition rate (the number of pulses emitted per unit of time - second) is measured in Hz and kHz.
• Pulse duration (time length of one pulse), measured in seconds. and microseconds.
• Ultrasound intensity is the ratio of wave power to the area over which the ultrasonic flow is distributed. It is measured in watts per square centimeter and, as a rule, does not exceed 0.01 W/sq.cm.

Modern ultrasound devices use ultrasound with a frequency of 2 to 15 MHz to obtain images.

In ultrasound diagnostics, sensors with frequencies of 2.5 are usually used; 3.0; 3.5; 5.0; 7.5 megahertz. The lower the frequency of ultrasound, the greater the depth of its penetration into tissue; ultrasound with a frequency of 2.5 MHz penetrates up to 24 cm, 3-3.5 MHz - up to 16-18 cm; 5.0 MHz – up to 9-12 cm; 7.5 MHz up to 4-5 cm. For heart research, the frequency used is 2.2-5 MHz, in ophthalmology - 10-15 MHz.

Biological effect of ultrasound

and its safety for the patient is constantly debated in the literature. Ultrasound can cause biological effects through mechanical and thermal effects. Attenuation of the ultrasonic signal occurs due to absorption, i.e. converting ultrasonic wave energy into heat. Tissue heating increases with increasing intensity of emitted ultrasound and its frequency. A number of authors note the so-called. cavitation is the formation in a liquid of pulsating bubbles filled with gas, steam or a mixture of both. One of the causes of cavitation may be an ultrasonic wave.

Research related to the effects of ultrasound on cells, experimental work in plants and animals, and epidemiological studies have led the American Ultrasound Institute to make the following statement:

“There have never been any documented biological effects in patients or device operators caused by exposure to ultrasound at the intensity typical of modern diagnostic ultrasound units. Although it is possible that such biological effects may be identified in the future, current evidence indicates that the benefit to the patient from the prudent use of diagnostic ultrasound outweighs the potential risk, if any."

To study which organs and systems is the ultrasound method used?

• Parenchymal organs of the abdominal cavity and retroperitoneal space, including the pelvic organs (embryo and fetus).
• Cardiovascular system.
• Thyroid and mammary glands.
• Soft fabrics.
• Newborn brain.

What criteria are used in ultrasound examinations:

1. CONTOURS – clear, even, uneven.
2. ECHO STRUCTURE:

• Liquid;
• Semi-liquid;
• Fabric - greater or lesser density.

Ultrasound research methods

1. Concept of KM

Ultrasonic waves are elastic vibrations of a medium with a frequency that lies above the range of sounds audible to humans - above 20 kHz. The upper limit of ultrasonic frequencies can be considered 1 – 10 GHz. This limit is determined by intermolecular distances and therefore depends on the state of aggregation of the substance in which ultrasonic waves propagate. They have a high penetrating ability and pass through body tissues that do not transmit visible light. Ultrasound waves are non-ionizing radiation and, in the range used in diagnostics, do not cause significant biological effects. In terms of average intensity, their energy does not exceed when using short pulses of 0.01 W/cm 2 . Therefore, there are no contraindications to the study. The ultrasound diagnostic procedure itself is short, painless, and can be repeated many times. The ultrasonic installation takes up little space and does not require any protection. It can be used to examine both inpatient and outpatient patients.

Thus, the ultrasound method is a method for remotely determining the position, shape, size, structure and movements of organs and tissues, as well as pathological foci using ultrasound radiation. It ensures registration of even minor changes in the density of biological media. In the coming years, it is likely to become the main imaging modality in diagnostic medicine. Due to its simplicity, harmlessness and effectiveness, in most cases it should be used in the early stages of the diagnostic process.

To generate ultrasound, devices called ultrasound emitters are used. The most widespread are electromechanical emitters based on the phenomenon of the inverse piezoelectric effect. The inverse piezoelectric effect consists of mechanical deformation of bodies under the influence of an electric field. The main part of such an emitter is a plate or rod made of a substance with well-defined piezoelectric properties (quartz, Rochelle salt, ceramic material based on barium titanate, etc.). Electrodes are applied to the surface of the plate in the form of conductive layers. If an alternating electrical voltage from a generator is applied to the electrodes, the plate, thanks to the inverse piezoelectric effect, will begin to vibrate, emitting a mechanical wave of the corresponding frequency.

The greatest effect of mechanical wave radiation occurs when the resonance condition is met. Thus, for plates 1 mm thick, resonance occurs for quartz at a frequency of 2.87 MHz, Rochelle salt at 1.5 MHz, and barium titanate at 2.75 MHz.

An ultrasound receiver can be created based on the piezoelectric effect (direct piezoelectric effect). In this case, under the influence of a mechanical wave (ultrasonic wave), deformation of the crystal occurs, which leads, through the piezoelectric effect, to the generation of an alternating electric field; the corresponding electrical voltage can be measured.

The use of ultrasound in medicine is associated with the peculiarities of its distribution and characteristic properties. Let's consider this question. By its physical nature, ultrasound, like sound, is a mechanical (elastic) wave. However, the ultrasound wavelength is significantly less than the sound wavelength. Wave diffraction depends significantly on the ratio of the wavelength and the size of the bodies on which the wave diffracts. An “opaque” body 1 m in size will not be an obstacle to a sound wave with a length of 1.4 m, but will become an obstacle to an ultrasound wave with a length of 1.4 mm, and an “ultrasonic shadow” will appear. This makes it possible in some cases not to take into account the diffraction of ultrasonic waves, considering these waves as rays during refraction and reflection, similar to the refraction and reflection of light rays).

The reflection of ultrasound at the boundary of two media depends on the ratio of their wave impedances. Thus, ultrasound is well reflected at the boundaries of muscle - periosteum - bone, on the surface of hollow organs, etc. Therefore, it is possible to determine the location and size of heterogeneous inclusions, cavities, internal organs, etc. (ultrasonic location). Ultrasound location uses both continuous and pulsed radiation. In the first case, a standing wave is studied, which arises from the interference of incident and reflected waves from the interface. In the second case, the reflected pulse is observed and the time of propagation of ultrasound to the object under study and back is measured. Knowing the speed of propagation of ultrasound, the depth of the object is determined.

The wave resistance (impedance) of biological media is 3000 times greater than the wave resistance of air. Therefore, if an ultrasound emitter is applied to a human body, the ultrasound will not penetrate inside, but will be reflected due to a thin layer of air between the emitter and the biological object. To eliminate the air layer, the surface of the ultrasonic emitter is covered with a layer of oil.

The speed of propagation of ultrasonic waves and their absorption significantly depend on the state of the environment; This is the basis for the use of ultrasound to study the molecular properties of a substance. Research of this kind is the subject of molecular acoustics.

2. Source and receiver of ultrasonic radiation

Ultrasound diagnostics is carried out using an ultrasonic installation. It is a complex and at the same time quite portable device, made in the form of a stationary or mobile device. To generate ultrasound, devices called ultrasound emitters are used. The source and receiver (sensor) of ultrasonic waves in such an installation is a piezoceramic plate (crystal) located in the antenna (sound probe). This plate is an ultrasonic transducer. Alternating electric current changes the dimensions of the plate, thereby exciting ultrasonic vibrations. The vibrations used for diagnostics have a short wavelength, which allows them to be formed into a narrow beam directed to the part of the body being examined. The reflected waves are perceived by the same plate and converted into electrical signals. The latter are fed to a high-frequency amplifier and are further processed and presented to the user in the form of a one-dimensional (in the form of a curve) or two-dimensional (in the form of a picture) image. The first is called an echogram, and the second is called an ultrasonogram (sonogram) or ultrasound scan.

The frequency of ultrasonic waves is selected depending on the purpose of the study. For deep structures, lower frequencies are used and vice versa. For example, waves with a frequency of 2.25-5 MHz are used to study the heart, in gynecology - 3.5-5 MHz, and for echography of the eye - 10-15 MHz. In modern installations, echo and sonograms are subjected to computer analysis using standard programs. Information is printed in alphabetic and numeric form; it can be recorded on videotape, including in color.

All ultrasonic installations, except those based on the Doppler effect, operate in the pulse echolocation mode: a short pulse is emitted and the reflected signal is perceived. Depending on the research objectives, different types of sensors are used. Some of them are designed for scanning from the body surface. Other sensors are connected to an endoscopic probe and are used for intracavitary examination, including in combination with endoscopy (endosonography). These sensors, as well as probes designed for ultrasonic localization on the operating table, can be sterilized.

According to the principle of operation, all ultrasound devices are divided into two groups: pulse echo and Doppler. Devices of the first group are used to determine anatomical structures, their visualization and measurement. Devices of the second group make it possible to obtain kinematic characteristics of rapidly occurring processes - blood flow in vessels, heart contractions. However, this division is conditional. There are installations that make it possible to simultaneously study both anatomical and functional parameters.

3. Object of ultrasound examination

Due to its harmlessness and simplicity, the ultrasound method can be widely used in examining the population during clinical examination. It is indispensable when studying children and pregnant women. In the clinic, it is used to identify pathological changes in sick people. For examination of the brain, eyes, thyroid and salivary glands, breast, heart, kidneys, pregnant women with a term of more than 20 weeks. no special training required.

The patient is examined in different body positions and different positions of the hand probe (sensor). In this case, the doctor usually does not limit himself to standard positions. By changing the position of the sensor, it seeks to obtain the most complete information about the state of the organs. The skin over the part of the body being examined is lubricated with a product that transmits ultrasound well for better contact (vaseline or a special gel).

Ultrasound attenuation is determined by ultrasonic resistance. Its value depends on the density of the medium and the speed of propagation of the ultrasonic wave in it. Having reached the boundary of two media with different impedances, the beam of these waves undergoes a change: part of it continues to propagate in the new medium, and part of it is reflected. The reflection coefficient depends on the difference in impedance of the contacting media. The higher the difference in impedance, the more waves are reflected. In addition, the degree of reflection is related to the angle of incidence of the waves on the adjacent plane. The greatest reflection occurs at a right angle of incidence. Due to the almost complete reflection of ultrasonic waves at the boundaries of some media, during ultrasound examination one has to deal with “blind” zones: these are the air-filled lungs, the intestines (if there is gas in it), and areas of tissue located behind the bones. Up to 40% of waves are reflected at the boundary of muscle tissue and bone, and almost 100% are reflected at the boundary of soft tissue and gas, since gas does not conduct ultrasonic waves.

Three methods of ultrasound diagnostics are most widespread in clinical practice: one-dimensional examination (echography), two-dimensional examination (scanning, sonography) and Dopplerography. All of them are based on recording echo signals reflected from an object.

1) One-dimensional echography

At one time, the term “echography” meant any ultrasound examination, but in recent years it has been used mainly to describe a one-dimensional examination method. There are two options: A-method and M-method. With the A-method, the sensor is in a fixed position to record the echo signal in the direction of radiation. Echo signals are represented in one-dimensional form, as amplitude marks on the time axis. Hence, by the way, the name of the method. It comes from the English word amplitude. In other words, the reflected signal forms a figure on the indicator screen in the form of a peak on a straight line. The initial peak in the curve corresponds to the moment of generation of the ultrasonic pulse. Repeated peaks correspond to echoes from internal anatomical structures. The amplitude of the signal displayed on the screen characterizes the magnitude of the reflection (depending on the impedance), and the delay time relative to the start of the scan characterizes the depth of the inhomogeneity, i.e., the distance from the surface of the body to the tissues that reflected the signal. Consequently, the one-dimensional method provides information about the distances between tissue layers along the path of the ultrasound pulse.

The A-method has gained a strong position in the diagnosis of diseases of the brain, organ of vision, and heart. In the neurosurgery clinic it is used under the name echoencephalography to determine the size of the ventricles of the brain and the position of the median diencephalic structures. The displacement or disappearance of the peak corresponding to the midline structures indicates the presence of a pathological focus inside the skull (tumor, hematoma, abscess, etc.). The same method, called echoophthalmography, is used in the clinic of eye diseases to study the structure of the eyeball, vitreous opacities, retinal or choroidal detachment, and to localize a foreign body or tumor in the orbit. In the cardiology clinic, the structure of the heart is assessed using echocardiography. But here they use a variation of the A-method - the M-method (from the English motion - movement).

With the M-method, the sensor is also in a fixed position. The echo signal amplitude changes when registering a moving object (heart, vessel). If you shift the echogram by a small amount with each subsequent probing pulse, you get an image in the form of a curve, called an M-echogram. The sending frequency of ultrasonic pulses is high - about 1000 per 1 s, and the pulse duration is very short, only 1 μs. Thus, the sensor only works 0.1% of the time as an emitter, and 99.9% as a receiving device. The principle of the M-method is that electric current pulses generated in the sensor are transmitted to an electronic unit for amplification and processing, and then output to a cathode ray tube of a video monitor (echocardiography) or to a recording system - a recorder (echocardiography).

2) Ultrasound scanning (sonography)

Ultrasound scanning provides a two-dimensional image of organs. This method is also known as the B-method (from the English bright - brightness). The essence of the method is to move the ultrasound beam along the surface of the body during the study. This ensures that signals are recorded simultaneously or sequentially from many points of the object. The resulting series of signals serves to form an image. It appears on the indicator screen and can be recorded on Polaroid paper or film. This image can be studied with the eye, or it can be subjected to mathematical processing, determining the dimensions: area, perimeter, surface and volume of the organ under study.

During ultrasonic scanning, the brightness of each luminous point on the indicator screen is directly dependent on the intensity of the echo signal. A strong echo signal produces a bright light spot on the screen, while weak signals produce various shades of gray, even black (gray scale system). On devices with such an indicator, stones appear bright white, and formations containing liquid appear black.

Most ultrasound installations allow scanning with a beam of waves of relatively large diameter and at a high frame rate per second, when the time of movement of the ultrasound beam is much less than the period of movement of the internal organs. This provides direct observation on the indicator screen of organ movements (contractions and relaxations of the heart, respiratory movements of organs, etc.). Such studies are said to be carried out in real time (“real-time” research).

The most important element of an ultrasound scanner, providing real-time operation, is an intermediate digital memory unit. In it, the ultrasound image is converted into a digital one and accumulates as signals are received from the sensor. At the same time, the image is read from memory by a special device and presented at the required speed on the television screen. Intermediate memory has another purpose. Thanks to it, the image has a half-tone character, the same as an x-ray. But the range of gray gradations on an x-ray does not exceed 15-20, and in an ultrasonic installation it reaches 64 levels. Intermediate digital memory allows you to stop the image of a moving organ, that is, take a “freeze frame” and carefully study it on the TV monitor screen. If necessary, this image can be captured on film or Polaroid paper. You can record the movements of the organ on magnetic media - disk or tape.

3) Dopplerography

Dopplerography is one of the most elegant instrumental techniques. It is based on the Doppler principle. It states: the frequency of the echo signal reflected from a moving object is different from the frequency of the emitted signal. The source of ultrasonic waves, as in any ultrasonic installation, is an ultrasonic transducer. It is motionless and forms a narrow beam of waves directed to the organ under study. If this organ moves during the observation process, then the frequency of the ultrasonic waves returning to the transducer differs from the frequency of the primary waves. If an object moves towards a stationary sensor, it encounters more ultrasonic waves in the same period of time. If the object moves away from the sensor, then there are fewer waves.

Dopplerography is an ultrasound diagnostic method based on the Doppler effect. The Doppler effect is a change in the frequency of ultrasonic waves perceived by the sensor, which occurs as a result of the movement of the object under study relative to the sensor.

There are two types of Doppler studies - continuous and pulsed. In the first, the generation of ultrasonic waves is carried out continuously by one piezocrystal element, and the registration of reflected waves is carried out by another. In the electronic unit of the device, two frequencies of ultrasonic vibrations are compared: those directed at the patient and those reflected from him. By the shift in the frequencies of these oscillations, the speed of movement of anatomical structures is judged. Frequency shift analysis can be done acoustically or using recorders.

Continuous Doppler sonography is a simple and accessible research method. It is most effective at high blood flow rates, which occur, for example, in areas of narrowing of blood vessels. However, this method has a significant drawback. A change in the frequency of the reflected signal occurs not only due to the movement of blood in the vessel under study, but also due to any other moving structures that occur in the path of the incident ultrasonic wave. Thus, with continuous Doppler ultrasound, the total speed of movement of these objects is determined.

Pulsed Dopplerography is free from this disadvantage. It allows you to measure speed in a control volume area specified by the doctor. The dimensions of this volume are small - only a few millimeters in diameter, and its position can be arbitrarily set by the doctor in accordance with the specific task of the study. In some devices, blood flow speed can be determined simultaneously in several control volumes - up to 10. Such information reflects the complete picture of blood flow in the studied area of ​​the patient's body. Let us point out, by the way, that the study of blood flow velocity is sometimes called ultrasonic fluorimetry.

The results of a pulsed Doppler study can be presented to the doctor in three ways: in the form of quantitative indicators of blood flow velocity, in the form of curves, and auditorily, i.e., tonal signals at the sound output. The sound output allows one to differentiate by ear a homogeneous, regular, laminar flow of blood and a vortex turbulent blood flow in a pathologically altered vessel. When recorded on paper, laminar blood flow is characterized by a thin curve, while vortex blood flow is shown by a broad and heterogeneous curve.

The greatest capabilities are provided by installations for two-dimensional Doppler ultrasound in real time. They provide a special technique called angiodynography. In these installations, through complex electronic transformations, visualization of blood flow in the vessels and chambers of the heart is achieved. In this case, the blood moving towards the sensor is colored red, and from the sensor - blue. The color intensity increases with increasing blood flow speed. Color-coded two-dimensional scans are called angiograms.

Doppler sonography is used clinically to study the shape, contours and lumens of blood vessels. The fibrous wall of the vessel is a good reflector of ultrasound waves and is therefore clearly visible on sonograms. This makes it possible to detect narrowing and thrombosis of blood vessels, individual atherosclerotic plaques in them, blood flow disorders, and determine the state of collateral circulation.

In recent years, the combination of sonography and Dopplerography (so-called duplex sonography) has become especially important. It produces both an image of the vessels (anatomical information) and a recording of the blood flow curve in them (physiological information). There is a possibility of direct non-invasive research for diagnosing occlusive lesions of various vessels with simultaneous assessment of blood flow in them. In this way, they monitor the blood filling of the placenta, contractions of the fetal heart, the direction of blood flow in the chambers of the heart, determine the reverse flow of blood in the portal vein system, calculate the degree of vascular stenosis, etc.

Ultrasound examination (Ultrasound), sonography- non-invasive examination of the human or animal body using ultrasonic waves.

Encyclopedic YouTube

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✪ Ultrasound examination

✪ Ultrasound examination of the prostate gland (echosemiotics of structural changes).

✪ Procedure: ultrasound examination of the gallbladder, part 1 - introduction

✪ ultrasound examination of the abdominal cavity - examination of the aorta using a specific example

✪ Ultrasound anatomy and liver examination techniques

Subtitles

Physical Basics

Having reached the boundary of two media with different acoustic resistance, the beam of ultrasonic waves undergoes significant changes: one part of it continues to propagate in the new medium, being absorbed to one degree or another by it, the other is reflected. The reflection coefficient depends on the difference in the acoustic resistance of tissues adjacent to each other: the greater this difference, the greater the reflection and, naturally, the greater the intensity of the recorded signal, which means the lighter and brighter it will appear on the device screen. A complete reflector is the boundary between tissue and air.

In its simplest implementation, the method allows you to estimate the distance to the separation boundary of the densities of two bodies, based on the travel time of the wave reflected from the separation boundary. More complex research methods (for example, based on the Doppler effect) make it possible to determine the speed of movement of the density interface, as well as the difference in the densities forming the boundary.

When propagating, ultrasonic vibrations obey the laws of geometric optics. In a homogeneous medium they propagate rectilinearly and at a constant speed. At the boundary of different media with unequal acoustic density, some of the rays are reflected, and some are refracted, continuing their linear propagation. The higher the gradient of the difference in the acoustic density of the boundary media, the larger part of the ultrasonic vibrations is reflected. Since 99.99% of vibrations are reflected at the boundary of the transition of ultrasound from air to skin, when ultrasound scanning a patient it is necessary to lubricate the skin surface with aqueous jelly, which acts as a transition medium. Reflection depends on the angle of incidence of the beam (greatest when the direction is perpendicular) and the frequency of ultrasonic vibrations (at higher frequencies, more is reflected).

To study the abdominal organs and retroperitoneal space, as well as the pelvic cavity, a frequency of 2.5 - 3.5 MHz is used, and a frequency of 7.5 MHz is used to study the thyroid gland.

Of particular interest in diagnostics is the use of the Doppler effect. The essence of the effect is a change in the frequency of sound due to the relative movement of the sound source and receiver. When sound bounces off a moving object, the frequency of the reflected signal changes (a frequency shift occurs).

When the primary and reflected signals overlap, beats occur, which can be heard using headphones or a loudspeaker.

Components of an ultrasound diagnostic system

Ultrasonic Wave Generator

The generator of ultrasonic waves is a sensor, which simultaneously plays the role of a receiver of reflected echo signals. The generator operates in pulse mode, sending about 1000 pulses per second. In the intervals between the generation of ultrasonic waves, the piezo sensor records the reflected signals.

Ultrasonic sensor

A complex sensor consisting of several hundred small piezocrystalline transducers operating in the same mode is used as a detector or transducer. A focusing lens is built into the sensor, which makes it possible to create focus at a certain depth.

Types of sensors

All ultrasonic sensors are divided into mechanical and electronic. In mechanical scanning, scanning is carried out due to the movement of the emitter (it either rotates or swings). In electronic scanning, scanning is done electronically. The disadvantages of mechanical sensors are noise and vibration produced when the emitter moves, as well as low resolution. Mechanical sensors are obsolete and are not used in modern scanners. Three types of ultrasonic scanning are used: linear (parallel), convex and sector. Accordingly, the sensors or transducers of ultrasonic devices are called linear, convex and sector. The choice of sensor for each study is carried out taking into account the depth and nature of the position of the organ.

Linear sensors

In clinical practice, the technique is used in two directions.

Dynamic echo contrast angiography

The visualization of blood flow is significantly improved, especially in small, deeply located vessels with low blood flow velocity; the sensitivity of the color circulation and edema significantly increases; provides the ability to observe all phases of vascular contrast in real time; the accuracy of assessing stenotic lesions of blood vessels increases.

Tissue echo contrast

It is ensured by the selectivity of the inclusion of echo contrast agents in the structure of certain organs. The degree, speed and accumulation of echo contrast in unchanged and pathological tissues are different. It becomes possible to assess organ perfusion, improves contrast resolution between normal and diseased tissue, which helps to increase the accuracy of diagnosis of various diseases, especially malignant tumors.

Application in medicine

Echoencephalography

Echoencephalography, like Dopplerography, is found in two technical solutions: A-mode (in the strict sense, it is not considered an ultrasound examination, but is performed as part of functional diagnostics) and B-mode, which has received the unofficial name “neurosonography”. Since ultrasound cannot effectively penetrate bone tissue, including the skull bones, neurosonography is performed mainly on infants through the large fontanelle) and is not used to diagnose the brain in adults. However, materials have already been developed that will help ultrasound penetrate the bones of the body.

The use of ultrasound for diagnosis of serious head injuries allows the surgeon to determine the location of hemorrhages. Using a handheld probe, the position of the midline of the brain can be established in approximately one minute. The operating principle of such a probe is based on recording an ultrasonic echo from the interface between the hemispheres.

Ophthalmology

Just like echoencephalography, it exists in two technical solutions (different devices): A-mode (usually not considered ultrasound) and B-mode.

Ultrasound probes are used to measure the size of the eye and determine the position of the lens.

Internal diseases

Ultrasound plays an important role in diagnosing diseases of internal organs, such as:

• abdominal cavity and retroperitoneal space
  • gallbladder and biliary tract
• pelvic organs

Due to its relatively low cost and high availability, ultrasound is a widely used method for examining a patient and allows diagnosing a fairly large number of diseases, such as cancer, chronic diffuse changes in organs (diffuse changes in the liver and pancreas, kidneys and renal parenchyma, prostate gland, the presence of stones in the gall bladder, kidneys, the presence of anomalies of internal organs, fluid formations in organs.

Due to physical characteristics, not all organs can be reliably examined by ultrasound; for example, the hollow organs of the gastrointestinal tract are difficult to access due to the gas content in them. However, ultrasound diagnostics can be used to determine signs of intestinal obstruction and indirect signs of adhesions. Using ultrasound, you can detect the presence of free fluid in the abdominal cavity, if there is enough of it, which can play a decisive role in the treatment tactics of a number of therapeutic and surgical diseases and injuries.

Liver

Ultrasound examination of the liver is quite highly informative. The doctor evaluates the size of the liver, its structure and homogeneity, the presence of focal changes, as well as the state of blood flow. Ultrasound allows one to detect with fairly high sensitivity and specificity both diffuse changes in the liver (fatty hepatosis, chronic hepatitis and cirrhosis) and focal ones (fluid and tumor formations). It should definitely be added that any ultrasound findings of both the liver and other organs must be evaluated only together with clinical, anamnestic data, as well as data from additional examinations.

Gallbladder and bile ducts

In addition to the liver itself, the condition of the gallbladder and bile ducts is assessed - their size, wall thickness, patency, the presence of stones, and the condition of surrounding tissues are examined. Ultrasound allows in most cases to determine the presence of stones in the cavity of the gallbladder.

Pancreas

Diagnostic fetal ultrasound is also generally considered a safe method for use during pregnancy. This diagnostic procedure should be used only if there are compelling medical indications, with the shortest possible duration of ultrasound exposure that will allow obtaining the necessary diagnostic information, that is, according to the minimum acceptable or ALARA principle.

The 1998 World Health Organization Report 875 supports the view that ultrasound is harmless. Despite the lack of data on the harm of ultrasound to the fetus, the US Food and Drug Administration considers the advertising, sale or rental of ultrasound equipment to create “fetal souvenir videos” as inappropriate, unauthorized use of medical equipment.

Ultrasound diagnostic device

Ultrasound diagnostic apparatus (ultrasound scanner) is a device designed to obtain information about the location, shape, size, structure, blood supply of organs and tissues of humans and animals.

Based on form factor, ultrasound scanners can be divided into stationary and portable (portable); by the mid-2010s, mobile ultrasound scanners based on smartphones and tablets became widespread.

Outdated classification of ultrasound machines

Depending on their functional purpose, devices are divided into the following main types:

• ETS - echotomoscopes (devices designed mainly for examining the fetus, abdominal and pelvic organs);
• EX - echocardioscopes (devices designed to study the heart);
• EES - echoenceloscopes (devices designed to study the brain);
• EOS - echo-ophthalmoscopes (devices designed to examine the eye).

Depending on the time of receiving diagnostic information, devices are divided into the following groups:

• C - static;
• D - dynamic;
• K - combined.

Device classifications

Officially, ultrasound machines can be divided according to the presence of certain scanning modes, measurement programs (packages, for example, cardio package - a program for echocardiographic measurements), high-density sensors (sensors with a large number of piezoelements, channels and, accordingly, higher transverse resolution), additional options (3D, 4D, 5D, elastography and others).

The term “ultrasound examination” in the strict sense can mean a study in B-mode; in particular, in Russia this is standardized and a study in A-mode is not considered an ultrasound. Old generation devices without B-mode are considered obsolete, but are still used as part of functional diagnostics.

The commercial classification of ultrasound devices generally does not have clear criteria and is determined independently by manufacturers and their dealer networks; characteristic classes of equipment are:

• Primary class (B-mode)
• Middle class (CDC)
• High class
• Premium class
• Expert class

Terms, concepts, abbreviations

• Advanced 3D- expanded 3D reconstruction program.
• ATO- Automatic image optimization, optimizes image quality with the click of a button.
• B-Flow- visualization of blood flow directly in B-mode without the use of Doppler methods.
• Coded Contrast Imaging Option- coded contrast image mode, used in studies with contrast agents.
• CodeScan- technology for amplifying weak echo signals and suppressing unwanted frequencies (noise, artifacts) by creating a coded sequence of pulses on transmission with the ability to decode them on reception using a programmable digital decoder. This technology allows for unsurpassed image quality and improved diagnostic quality through new scanning modes.
• Color doppler (CFM or CFA)- Color Doppler - highlighting on the echogram with color (color mapping) the nature of blood flow in the area of ​​interest. The blood flow to the sensor is usually mapped in red, and from the sensor - in blue. Turbulent blood flow is mapped in blue-green-yellow color. Color Doppler is used to study blood flow in vessels and in echocardiography. Other names for the technology are color Doppler mapping (CDC), color flow mapping (CFM) and color flow angiography (CFA). Typically, using color Doppler, changing the position of the sensor, the area of ​​interest (vessel) is found, then pulsed Doppler is used for quantitative assessment. Color and power Doppler help in differentiating cysts from tumors since the internal contents of a cyst are avascular and therefore can never have color loci.
• DICOM- the ability to transfer “raw” data over the network for storage on servers and workstations, printing and further analysis.
• Easy 3D- surface three-dimensional reconstruction mode with the ability to set the transparency level.
• M-mode- one-dimensional ultrasound scanning mode (historically the first ultrasound mode), in which anatomical structures are examined along the time axis, currently used in echocardiography. M-mode is used to assess the size and contractile function of the heart and the functioning of the valve apparatus. Using this mode, you can calculate the contractility of the left and right ventricles and evaluate the kinetics of their walls.
• MPEGvue- quick access to stored digital data and a simplified procedure for transferring images and video clips to CD in a standard format for subsequent viewing and analysis on a computer.
• Power doppler- power Doppler - qualitative assessment of low-speed blood flow, used in the study of a network of small vessels (thyroid gland, kidneys, ovary), veins (liver, testicles), etc. More sensitive to the presence of blood flow than color Doppler. The echogram is usually displayed in an orange palette; brighter shades indicate a higher blood flow rate. The main disadvantage is the lack of information about the direction of blood flow. The use of power Doppler in three-dimensional mode makes it possible to judge the spatial structure of blood flow in the scanning area. Power Doppler is rarely used in echocardiography, but is sometimes used in combination with contrast agents to study myocardial perfusion. Color and power Doppler help in differentiating cysts from tumors since the internal contents of a cyst are avascular and therefore can never have color loci.
• Smart Stress- expanded capabilities of stress echo studies. Quantitative analysis and the ability to save all scanning settings for each stage of the study when visualizing different segments of the heart.
• Tissue Harmonic Imaging (THI)- technology for isolating the harmonic component of vibrations of internal organs caused by the passage of a basic ultrasonic pulse through the body. The useful signal is the one obtained by subtracting the base component from the reflected signal. The use of the 2nd harmonic is advisable when ultrasound scanning through tissues that intensively absorb the 1st (basic) harmonic. The technology involves the use of broadband sensors and a high-sensitivity receiving path, which improves image quality, linear and contrast resolution in overweight patients. * Tissue Synchronization Imaging (TSI)- a specialized tool for the diagnosis and assessment of cardiac dysfunctions.
• Tissue Velocity Imaging, Tissue Doppler Imaging (TDI)- tissue Doppler - mapping tissue movement, used in TSD and TCDC modes (tissue spectral and color Dopplerography) in echocardiography to assess myocardial contractility. By studying the directions of movement of the walls of the left and right ventricles in systole and diastole with tissue Doppler, it is possible to detect hidden zones of impaired local contractility.
• TruAccess- an approach to image acquisition based on the ability to access “raw” ultrasound data.
• TruSpeed- a unique set of software and hardware components for processing ultrasound data, providing ideal image quality and the highest data processing speed in all scanning modes.
• Virtual Convex- expanded convex image when using linear and sector sensors.
• VScan- visualization and quantification of myocardial movement.
• Pulsed Doppler (PW, HFPW)- pulsed Doppler (Pulsed Wave or PW) is used to quantify blood flow in vessels. The vertical time base displays the flow velocity at the point under study. Flows that move toward the sensor are displayed above the baseline, and return flow (away from the sensor) is shown below. The maximum flow speed depends on the scanning depth, pulse frequency and has a limitation (about 2.5 m/s when diagnosing the heart). High-frequency pulsed Doppler (HFPW - high frequency pulsed wave) allows you to record higher flow velocities, but also has a limitation associated with distortion of the Doppler spectrum.
• Continuous wave doppler- Continuous Wave Doppler (CW) is used to quantify blood flow in vessels with high-speed flows. The disadvantage of the method is that flows are recorded throughout the entire scanning depth. In echocardiography, using continuous wave Doppler, you can calculate the pressure in the cavities of the heart and great vessels in one or another phase of the cardiac cycle, calculate the degree of significance of stenosis, etc. The main CW equation is the Bernoulli equation, which allows you to calculate the pressure difference or pressure gradient. Using the equation, you can measure the pressure difference between the chambers under normal conditions and in the presence of pathological, high-speed blood flow.