Ultrasound examination (sonography) is one of the most modern, informative and available methods 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 identify the slightest changes in organs and catch the disease at the stage when clinical symptoms has 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 ultra-high 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 examination 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 occur, accompanied by ultrasound radiation. The fluctuations are caused by a rapid change in the shape of single crystals.

Piezo transducer elements are the basic component 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 values ​​of two neighboring media. The absolute reflector is the area bordering between human body and air. 99.9% of the waves travel in the opposite direction from this interface.

When studying blood flow, more modern and deep technique, 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 objective assessment condition 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 hidden form rheumatism and ischemic heart disease, as well as identify neoplasms. There are no contraindications to this diagnostic procedure. If there are diagnosed chronic pathologies cardiovascular system It is advisable to undergo echocardiography at least once a year.

Ultrasound of the abdominal organs

Ultrasound abdominal cavity used to assess the condition of the liver, gall bladder, 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

Renal ultrasound can reveal cystic neoplasms, extension renal pelvis and the presence of stones (). This kidney study must be carried out when.

Ultrasound of the thyroid gland

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

Ultrasound of the pelvic organs

Pelvic ultrasound is necessary to assess the condition of the female organs reproductive system(uterus and ovaries). Diagnostics allows, among other things, to detect pregnancy by early stages. In men, the method makes it possible to identify pathological changes from 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 contact of the sensor with the surface of the body, a special gel is applied to the patient’s skin before the start of the study, which, in particular, includes styrene compounds and glycerin.

We recommend reading:

Ultrasound scanning is currently widely used in obstetrics and perinatal diagnostics, i.e. for examining the fetus for different dates 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. Optimal timing, of which the maximum can be obtained useful information- 10-12, 20-24 and 32-37 weeks.

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

• nonunion hard 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 the report World Organization healthcare, in the preparation of which data obtained in leading clinics in the world over many years were used, 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 apply 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 given the opportunity 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 gives 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 on a regular two-dimensional black and white picture Only a specialist can see something.

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 should 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.

Introduction

The increasing importance of visualization diagnostic techniques V clinical practice should be explained to medical students early in their education. The widespread and non-invasive nature of sonography requires today to familiarize tomorrow's doctors with this relatively safe technique. It is no secret that the overwhelming number of ultrasound diagnostic specialists have undergone and are undergoing primary specialization in the workplace, i.e. behind the back of a doctor conducting routine patient visits. If you're lucky, you manage to see enough wide range pathologies, no - only the most common diseases. As a result, the training of the doctor returning from such training suffers from large gaps in special education. IN practical work He faces a huge number of questions that require immediate answers.

At the same time, it should be emphasized that every sonographic diagnosis is only as good as the ultrasound technician. Misdiagnosis can be avoided through in-depth knowledge of anatomy and ultrasound morphology, unrelenting rigor and, when appropriate, comparison with other imaging studies. Initial success (“I can already see all the parenchymal organs”) should not lead to overconfidence during training. Really deep knowledge can only be obtained through long-term independent work in the clinic, accumulation practical experience, studying anatomical features norms and pathologies.

At the same time, carefully prepared didactic material reflecting many years clinical experience will stimulate and perhaps even inspire many students.

Theoretical foundations of the method

Sound is mechanical longitudinal wave, in which the particle vibrations are in the same plane as the direction of energy propagation. A wave carries energy, but not matter. Upper limit audible sound- 20000 Hz. Sound with a frequency exceeding this value is called ultrasound. Frequency is the number of complete oscillations (cycles) over a period of time of 1 second. The units of frequency are hertz (Hz) and megahertz (MHz). One hertz is one vibration per second. One megahertz = 1,000,000 hertz. Modern ultrasound devices use ultrasound with a frequency of 2 MHz and higher to obtain images.

To obtain ultrasound, special converters or transducers are used, which convert electrical energy into ultrasound energy. Receiving ultrasound is based on the inverse piezoelectric effect, exercises. The essence of the effect is that if electric voltage is applied to certain materials (piezoelectrics), their shape will change. For this purpose, artificial piezoelectrics, such as zirconate or lead titanate, are most often used in ultrasonic devices. In the absence 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 a fast alternating current is applied to a piezoelectric element, the element will start from high frequency contract and expand (i.e. oscillate), generating an ultrasonic field. The operating frequency of the transducer (resonant frequency) is determined by the ratio of the speed of propagation of ultrasound in the piezoelectric element to the double thickness of this piezoelectric element. Detection of reflected signals is based on the direct piezoelectric effect. The returning signals cause the piezoelectric element to oscillate and an alternating electric current to appear on its edges. In this case, the piezoelectric element functions as ultrasonic sensor. Typically, ultrasonic devices use the same elements to emit and receive ultrasound. Therefore, the terms “converter”, “transducer”, “sensor” are synonymous.

Unlike electromagnetic waves(light, radio waves, etc.) sound requires a medium to propagate - it cannot propagate in a vacuum. Like all waves, sound can be described by a number of parameters. In addition to frequency, these are wavelength, propagation speed in the medium, period, amplitude and intensity. Frequency, period, amplitude and intensity are determined by the sound source, the speed of propagation is determined by the medium, and the wavelength is determined by both the sound source and the medium.

The period is the time required to obtain one complete cycle of oscillations. The units of period are second (s) and microsecond (µs). One microsecond is one millionth of a second. Period (µs) = 1/frequency (MHz).

Wavelength is the length that one vibration occupies in space. Units of measurement are meter (m) and millimeter (mm). The speed of ultrasound is the speed at which the wave travels through a medium. The units of ultrasound propagation speed are meters per second (m/s) and millimeters per microsecond (mm/µs). The speed of ultrasound propagation is determined by the density and elasticity of the medium. The speed of ultrasound propagation increases with increasing elasticity and decreasing density of the medium.

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

This value, entered into a computer program, is based on the assumption that the speed of sound propagation in tissue is constant. However, sound travels through the liver at a speed of about 1570 m/s, while through adipose tissue goes at a lower speed - about 1476 m/s. The estimated average speed that is stored in the computer causes some variation, but does not cause much distortion.

The speed of propagation of ultrasound (C), frequency (f) and wavelength () are related to each other the following equation: C=f x.

Since in our case the speed is considered constant (1540 m/s), the remaining two variables f are interconnected by an inversely proportional relationship. The higher the frequency, the shorter the wavelength and the smaller sizes objects that we can see.

To obtain an image in ultrasound diagnostics, it is not ultrasound that is emitted by a transducer continuously (constant wave), but ultrasound emitted in the form of short pulses (pulsed).

These vibrations are emitted by the crystal (piezoelectric effect) as a sound wave in the same way that sound waves are emitted by a loudspeaker membrane, although the frequencies used in sonography are not audible to the human ear.

Depending on the purpose of application, the monographic frequency can be from 2.0 to 15.0 MHz.

Additional parameters are used to characterize pulsed ultrasound. The pulse repetition rate is the number of pulses emitted per unit of time (second). Pulse repetition frequency is measured in hertz (Hz) and kilohertz (kHz).

Pulse duration is the time duration of one pulse.

Measured in seconds (s) and microseconds (µs).

The occupancy factor is the fraction of time during which ultrasound is emitted (in the form of pulses).

Spatial pulse extension (SPR) is the length of space in which one ultrasonic pulse is placed.

For soft tissues, the spatial extent of the pulse (mm) is equal to the product of 1.54 (ultrasound propagation speed in mm/µs) and the number of oscillations (cycles) in the pulse (n) divided by the frequency in MHz. Or, PPI = 1.54xn/f.

Reducing the spatial extent of the pulse can be achieved (and this is very important for improving axial resolution) by reducing the number of oscillations in the pulse or increasing the frequency.

The amplitude of an ultrasonic wave is the maximum deviation of an observed physical variable from the mean value

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 (W/sq.cm).

With equal radiation power than smaller area flow, the higher the intensity. The intensity is also proportional to the square of the amplitude. So, if the amplitude doubles, then the intensity quadruples. The intensity is non-uniform both over the flow area and, in the case of pulsed ultrasound, over time.

When passing through any medium, there will be a decrease in the amplitude and intensity of the ultrasonic signal, which is called attenuation. Ultrasonic signal attenuation is caused by absorption, reflection and scattering. The unit of attenuation is decibel (dB). The attenuation coefficient is the attenuation of an ultrasonic signal per unit path length of this signal (dB/cm). The attenuation coefficient increases with increasing frequency.

Sound waves from the sensor, which consists of many crystals, penetrate the tissue, are reflected and return as an echo to the sensor. The returning echoes are reversely converted by the crystals into electrical impulses and are then used by a computer to construct a sonographic image.

Refraction is a change in the direction of propagation of an ultrasonic beam when it crosses the boundary of media with different ultrasound propagation speeds. The sine of the angle of refraction is equal to the product of the sine of the angle of incidence by the value obtained by dividing the speed of propagation of ultrasound in the second medium by the speed in the first. The sine of the refraction angle, and, consequently, the refraction angle itself, the greater the difference in the speed of propagation of ultrasound in two media. Refraction is not observed if the speeds of propagation of ultrasound in two media are equal or the angle of incidence is 0. Speaking about reflection, it should be borne in mind that in the case when the wavelength is many more sizes irregularities of the reflecting surface, specular reflection occurs.

Another important environmental parameter is acoustic resistance.

Acoustic resistance is the product of the density of the medium and the speed of propagation of ultrasound. Resistance (Z) = density () x speed of propagation (C).

When ultrasound passes through tissue at the interface of media with different acoustic resistance and speed of ultrasound, the phenomena of reflection, refraction, scattering and absorption occur. Depending on the angle, they speak of perpendicular and oblique (at an angle) incidence of the ultrasonic beam. When the ultrasonic beam is incident obliquely, the angle of incidence, angle of reflection and angle of refraction are determined. Angle of incidence equal to angle reflections. When the ultrasonic beam is incident perpendicularly, it can be completely reflected or partially reflected, partially passed through the boundary of two media; in this case, the direction of ultrasound passing from one medium to another does not change. The intensity of reflected ultrasound and ultrasound that has passed the boundary of the media depends on the initial intensity and the difference in the acoustic resistance of the media. The ratio of the intensity of the reflected wave to the intensity of the incident wave is called the reflection coefficient. The ratio of the intensity of the ultrasonic wave passing through the boundary of the media to the intensity of the incident wave is called the ultrasound conductivity coefficient. Thus, if tissues have different densities, but the same acoustic resistance, there will be no ultrasound reflection. On the other hand, with a large difference in acoustic resistance, the reflection intensity tends to 100%. An example of this is the air/soft tissue page. At the boundary of these media, almost complete reflection of ultrasound occurs. To improve the conduction of ultrasound in human body tissue, connecting media (gel) are used. Sound waves are reflected from the interface between media with different acoustic densities (i.e. different sound propagation). The reflection of sound waves is proportional to the difference in acoustic density: a moderate difference will reflect and return part of the sound beam to the transducer, the remaining sound waves will be transmitted and penetrate further into the deeper layers of tissue. If the difference in acoustic density is greater, the intensity of the reflected sound also increases, and the intensity of the sound that penetrates further decreases proportionately. If the acoustic density varies significantly, the sound beam is completely reflected, resulting in a total acoustic shadow (total reflection). Acoustic shadowing occurs behind bones (ribs), stones (kidney or gall bladder), and gas (gas in the intestines).

Echoes do not appear unless there is a difference in the acoustic density of the adjacent media: homogeneous fluids (blood, bile, urine and cyst contents, as well as ascitic fluid and pleural effusion) appear as echo-negative (black) structures, for example, gallbladder and hepatic vessels.

The processor of the ultrasound machine calculates the depth at which the echo occurred by recording the time difference between the moments of emission of the acoustic wave and the reception of the echo signal. Echoes from tissues close to the transducer return earlier than those from deeper tissues.

If the wavelength is comparable to the unevenness of the reflecting surface or there is inhomogeneity of the medium itself, ultrasound scattering occurs. In backscattering, ultrasound is reflected in the direction from which the original beam came. The intensity of scattered signals increases with increasing heterogeneity of the medium and increasing frequency (i.e. decreasing wavelength) of ultrasound. Scattering depends relatively little on the direction of the incident beam and, therefore, allows better visualization of reflective surfaces, not to mention organ parenchyma. In order for the reflected signal to be correctly located on the screen, it is necessary to know not only the direction of the emitted signal, but also the distance to the reflector. This distance is equal to 1/2 the product of the speed and ultrasound in the medium and the time between emission and reception of the reflected signal. The product of speed and time is divided in half, since ultrasound travels a double path (from the emitter to the reflector and back), and we are only interested in the distance from the emitter to the reflector.

At the same time, before returning to the sensor, the echo can be reflected back and forth several times, which takes a travel time that does not correspond to the distance to where it originated. The processor of the ultrasound machine mistakenly places these reverberation signals in a deeper layer.

Application in general medical practice

It is known that the passage of ultrasound through biological objects causes two types of effects: mechanical and thermal. Absorption of the energy of a sound wave leads to its attenuation, and the released energy is transformed into heat. Moreover, the severity of heating is interconnected with the intensity of ultrasonic radiation. A special case of the biological effects of ultrasound is cavitation. In this case, many pulsating bubbles filled with gas, steam or a mixture of both are formed in the sonicated liquid.

Rice. 1. Test object of the American Institute of Ultrasound in Medicine

The American Institute of Ultrasound in Medicine, based on a review of studies of the effects of ultrasound on plant and animal cells in 1993, made the following statement: “There have never been any documented biological effects in patients or device operators caused by irradiation (ultrasound) at the intensity of typical for modern ultrasound diagnostic installations. Although it is possible that such biological effects may be identified in the future, current evidence indicates that the benefit to the patient from prudent use of diagnostic ultrasound outweighs the potential risk, if any.

There is constant improvement in ultrasonic diagnostic devices and the rapid development of ultrasound diagnostics.

It seems promising to further improve Doppler techniques, especially such as power Doppler and Doppler color imaging of tissue.

A variant of color Doppler mapping is called “Power Doppler”. With power Doppler, it is not the value of the Doppler shift in the reflected signal that is determined, but its energy. This approach makes it possible to increase the sensitivity of the method to low speeds, make it almost angle independent, however, at the cost of losing the ability to determine the absolute value of the speed and direction of the flow.

In the future, three-dimensional echography may become a very important area of ​​​​ultrasound diagnostics. Today, there are several commercially available ultrasound diagnostic units that allow three-dimensional image reconstruction, however, the question of the clinical significance of this direction remains open.

At the end of the sixties of the last millennium, ultrasonic contrast agents were first used. For visualization of the right heart, there is currently a commercially available contrast “Echovist” (Schering). The next generation drug, obtained by reducing the size of contrast particles, can be recycled into circulatory system person (“Levovist”, Schering). This contrast significantly improves the Doppler signal, both spectral and color, which can be essential for assessing tumor blood flow.

The use of ultrathin sensors in intracavitary echography opens up new opportunities for the study of hollow organs and structures. At the same time, wide application This technique is limited by the high cost of specialized sensors, which, moreover, can be used for research a limited number of times.

Very promising direction objectification of the information obtained during ultrasound is computer image processing. In this case, it becomes possible to improve the accuracy of diagnosis of minor structural changes in parenchymal organs. However, the results obtained to date do not have significant clinical significance.

Basic information about the equipment used

As a typical example of sonographic equipment, consider the design of a middle-class device (Fig. 2).

Rice. 2. Ultrasonic device control panel (Toshiba)

First of all, you must enter the patient's name (A, B) correctly in order to correctly identify the image in the future. Keys for changing the image processing program (C) or Lsugopa sensor (D) are located in the upper half of the control panel. On most panels, the image freeze key (FREEZE) (E) is located on the right bottom corner. After pressing it, the ultrasound image freezes in real time. We recommend keeping your left finger at the ready at all times. This reduces any delay in stopping the desired image for measurement, examination or printing. The GAIN control (F) is used to generally enhance the received echo signals. To selectively control echoes at different depths, gain can be selectively changed using sliders (G), compensating for depth-related signal losses. Using the knob (I), you can move the image up or down, increase or decrease the size of the field of view, and place marks or markers for measurement anywhere on the screen. The “kolobok” operating mode (measuring or entering comments) is set using the corresponding keys. To facilitate subsequent study of the sonogram, it is recommended that before displaying the image on the printer (M), select the appropriate body marker (L) and use the “bloom” (I) to mark the position of the sensor. The remaining functions are not so important and can be learned later while working with the device.

The heart of modern sonographic complexes is the main pulse generator (in modern devices - a powerful processor), which controls all systems of the ultrasound device. The pulse generator sends electrical pulses to the transducer, which generates an ultrasonic pulse and sends it to the tissue, receives the reflected signals, converting them into electrical vibrations. These electrical oscillations are then sent to a radio frequency amplifier, to which a time-amplitude gain controller (VAG, tissue absorption depth compensation regulator) is usually connected. Due to the fact that the attenuation of the ultrasonic signal in tissue occurs according to an exponential law, the brightness of objects on the screen progressively increases with increasing depth. falls. Using a linear amplifier, i.e. an amplifier that proportionally amplified all signals would result in over-amplification of signals in the immediate vicinity of the sensor when attempting to improve imaging of deep objects. The use of logarithmic amplifiers can solve this problem. The ultrasound signal is amplified in proportion to the delay time of its return - the later it returns, the stronger the amplification. Thus, the use of VAG makes it possible to obtain an image on the screen of the same brightness in depth. The RF electrical signal thus amplified is then fed to the demodulator, where it is rectified and filtered and again amplified by a video amplifier and sent to the monitor screen.

To save the image on the monitor screen, video memory is required. It can be divided into analog and digital. The first monitors made it possible to present information in analog bistable form. A device called a discriminator made it possible to change the discrimination threshold - signals whose intensity was below the discrimination threshold did not pass through it and the corresponding areas of the screen remained dark. Signals whose intensity exceeded the discrimination threshold were presented on the screen as white dots. In this case, the brightness of the dots did not depend on the absolute value of the intensity of the reflected signal - all white dots had the same brightness. With this method of image presentation - it was called “bistable” - the boundaries of organs and structures with high reflectivity (for example, the renal sinus) were clearly visible, however, it was not possible to assess the structure of parenchymal organs. The appearance in the 70s of devices that made it possible to transmit shades on the monitor screen gray, marked the beginning of the era of gray scale instruments. These devices made it possible to obtain information that was unattainable when using devices with a bistable image. The development of computer technology and microelectronics soon made it possible to move from analogue images to digital ones. Digital images in ultrasound machines are formed on large matrices (usually 512x512 pixels) with a number of grayscale levels of 16-32-64-128-256 (4-5-6-7-8 bits). When visualizing to a depth of 20 cm on a 512x512 pixel matrix, one pixel will correspond to linear dimensions of 0.4 mm. On modern devices there is a tendency to increase the size of displays without loss of image quality and on mid-range devices (12 inch<30 см по диагонали) экран становится обычным явле­нием.

An ultrasonic device's cathode ray tube (display, monitor) uses a sharply focused beam of electrons to produce a bright spot on a screen coated with a special phosphor. Using deflection plates, this spot can be moved across the screen. With an A-type scan (A - instead of the English word “amplitude” (Amplitude)), the distance from the sensor is plotted along one axis, and the intensity of the reflected signal is plotted along the other. In modern devices, A-type scanning is practically not used. The B-type scan (B - instead of the English word “brightness”) allows along the scanning line to obtain information about the intensity of reflected signals in the form of differences in the brightness of individual points making up this line. M-type (sometimes TM) scan (M - instead the English word “motion” (Motion) allows you to register the movement (movement) of reflecting structures in time. In this case, the movements of reflecting structures in the form of points of different brightness are recorded vertically, and the displacement of the position of these points in time is recorded horizontally to obtain a two-dimensional tomographic. image, it is necessary to move the scanning line along the scanning plane in one way or another. In slow scanning devices, this was achieved by moving the sensor along the surface of the patient’s body manually.

Sonography machines currently in use can accommodate a variety of transducer types, allowing for in-office use ultrasound diagnostics, and in intensive care and emergency departments. The sensors are usually stored on a holding rack on the right side of the machine.

Ultrasonic sensors are complex devices and, depending on the image scanning method, are divided into sensors for slow scanning devices (single-element) and fast scanning (real-time scanning) - mechanical and electronic. Mechanical sensors can be single- or multi-element (anular). The scanning of the ultrasonic beam can be achieved by swinging the element, rotating the element or swinging the acoustic mirror. The image on the screen in this case has the shape of a sector (sector sensors) or a circle (circular sensors). Electronic sensors are multi-element and, depending on the shape of the resulting image, can be sector, linear, convex (convex). Image scanning in a sector sensor is achieved by swinging the ultrasonic beam with its simultaneous focusing. Sector sensors produce a fan-shaped image that is narrow near the sensor and widens as depth increases. Such divergent sound propagation can be achieved through the mechanical movement of piezoelectric elements. Sensors using this principle are cheaper, but have poor wear resistance. The electronic version (phase control) is more expensive and is used primarily in cardiology. Their operating frequency is 2.5-3.0 MHz. Interference associated with sound reflection from the ribs can be avoided by placing the sensor in the intercostal spaces and choosing the optimal beam divergence in the range of 60-90° to increase penetration depth. The disadvantages of these types of sensors are low resolution in the near field, a decrease in the number of scan lines with increasing depth (spatial resolution), and difficulty in handling.

In linear and convex sensors, image scanning is achieved by exciting a group of elements with their step-by-step movement along the antenna array with simultaneous focusing.

A single-element disc-shaped transducer in continuous emission mode produces an ultrasonic field, the shape of which changes depending on the distance. In some cases, additional ultrasonic “flows”, called side lobes, may be observed. The distance from the disk by the length of the near field (zone) is called the near zone. The zone beyond the near boundary is called far. The near-zone burnout is equal to the ratio of the square of the transducer diameter to 4 wavelengths. In the far zone, the diameter of the ultrasonic field increases. The place where the ultrasonic beam narrows the most is called the focus area, and the distance between the transducer and the focus area is called the focal length. There are different ways to focus the ultrasound beam. The simplest way to focus is an acoustic lens. With its help, you can focus the ultrasonic beam at a certain depth, which depends on the curvature of the lens. This focusing method does not allow you to quickly change the focal length, which is inconvenient in practical work.

Another focusing method is to use an acoustic mirror. In this case, by changing the distance between the mirror and the transducer, we will change the focal length. In modern devices with multi-element electronic sensors, the basis of focusing is electronic focusing. With an electronic focusing system, we can change the focal length from the instrument panel, however, for each image we will only have one focus area.

Since very short ultrasonic pulses are used to obtain images, emitted 1000 times per second (pulse repetition rate 1 kHz), the device works 99.9% of the time as a receiver of reflected signals. Having such a reserve of time, it is possible to program the device in such a way that when the image is first acquired, the near focus zone is selected and the information received from this zone is saved. Next - select the next focus area, receive information, save. And so on. The result is a composite image that is focused throughout its entire depth. It should, however, be noted that this method of focusing requires a significant amount of time to obtain one image (frame), which causes a decrease in the frame rate and flickering of the image. Why does so much effort go into focusing the ultrasound beam? The fact is that the narrower the beam, the better the lateral (lateral) resolution. Lateral resolution is the minimum distance between two objects located perpendicular to the direction of energy propagation, which are presented on the monitor screen as separate structures. The lateral resolution is equal to the diameter of the ultrasonic beam. Axial resolution is the minimum distance between two objects located along the direction of energy propagation, which are presented on the monitor screen as separate structures. Axial resolution depends on the spatial extent of the ultrasonic pulse - the shorter the pulse, the better the resolution. To shorten the pulse, both mechanical and electronic damping of ultrasonic vibrations is used. As a rule, axial resolution is better than lateral resolution.

Currently, slow (manual, complex) scanning devices are of only historical interest. They died morally with the advent of fast scanning devices (devices operating in real time). However, their main components are preserved in modern devices (naturally, using a modern element base).

Fast scanning devices, or as they are more often called, real-time devices, have now completely replaced slow or manual scanning devices. This is due to a number of advantages that these devices have: the ability to assess the movement of organs and structures in real time (i.e., at almost the same point in time); a sharp reduction in time spent on research; the ability to conduct research through small acoustic windows. If slow scanning devices can be compared to a camera (obtaining still images), then real-time devices can be compared to cinema, where still images (frames) replace each other with high frequency, creating the impression of movement. Fast scanning devices use, as mentioned above, mechanical and electronic sector sensors, electronic linear sensors, electronic convex (convex) sensors, and mechanical radial sensors. Some time ago, trapezoidal sensors appeared on a number of devices, the field of view of which had a trapezoidal shape; however, they did not show any advantages over convex sensors, but they themselves had a number of disadvantages.

Currently, the best sensor for examining the abdominal organs, retroperitoneal space and pelvis is a convex one. It has a relatively small contact surface and a very large field of view in the middle and far zones, which simplifies and speeds up the examination.

The operating frequencies of such sensors range from 2.5 MHz (in obese patients) to 5 MHz (in thin patients), with an average of 3.5-3.75 MHz. This design can be seen as a compromise between linear and sectoral sensors. A convex sensor provides a wide near and far image field and is easier to handle than a sector sensor. However, the density of scanning lines decreases with increasing distance from the sensor. When scanning the upper abdomen, the transducer must be carefully manipulated to avoid acoustic shadowing from the lower ribs.

When scanning with an ultrasonic beam, the result of each complete pass of the beam is called a frame. The frame is formed from a large number of vertical lines. Each ping is at least one ultrasonic pulse.

The pulse repetition rate for obtaining a gray scale image in modern devices is 1 kHz (1000 pulses per second). There is a relationship between pulse repetition frequency (PRF), the number of lines forming a frame, and the number of frames per unit time: PRF = number of lines x frame rate. On a monitor screen, the quality of the resulting image will be determined, in particular, by the line density. For a linear sensor, line density (lines/cm) is the ratio of the number of lines forming a frame to the width of the part of the monitor on which the image is formed. Linear transducers emit sound waves parallel to each other and create a rectangular image. The image width and number of scanning lines are constant throughout the entire depth. The advantage of linear sensors is their good resolution in the near field. These sensors are used primarily at high frequencies (5.0-7.5 MHz and higher) to study soft tissues and the thyroid gland. Their disadvantage is the large working surface area, which leads to the appearance of artifacts when applied to a curved body surface due to gas bubbles getting between the sensor and the skin. In addition, the acoustic shadow that forms from the ribs can spoil the image. In general, linear transducers are not suitable for imaging the chest or upper abdomen. For a sector-type sensor, line density (lines/degree) is the ratio of the number of lines forming a frame to the sector angle. The higher the frame rate set in the device, the lower (at a given pulse repetition rate) the number of lines forming the frame, the lower the density of lines on the monitor screen, the lower the quality of the resulting image. True, at a high frame rate we have good temporal resolution, which is very important for echocardiographic studies.

The ultrasound research method makes it possible to obtain not only information about the structural state of organs and tissues, but also to characterize the flows in the vessels. This ability is based on the Doppler effect - a change in the frequency of received sound when moving relative to the environment of the source or receiver of sound or a body scattering sound. It is observed due to the fact that the speed of propagation of ultrasound in any homogeneous medium is constant. Therefore, if a sound source moves at a constant speed, the sound waves emitted in the direction of movement seem to be compressed, increasing the frequency of the sound. The waves emitted in the opposite direction are stretched, causing the frequency of the sound to decrease. By comparing the original ultrasound frequency with the modified one, it is possible to determine the Doppler shifts and calculate the speed. It doesn't matter whether the sound is emitted by a moving object or whether the object reflects sound waves. In the second case, the source of ultrasound can be stationary (ultrasound sensor), and moving red blood cells can act as a reflector of ultrasonic waves. The Doppler shift can be either positive (if the reflector is moving towards the sound source) or negative (if the reflector is moving away from the sound source) if the direction of incidence of the ultrasonic beam is not parallel to the direction of movement of the reflector, it is necessary to correct the Doppler shift by the cosine of the angle and between incident beam and the direction of movement of the reflector. To obtain Doppler information, two types of devices are used - constant wave and pulsed. In a continuous wave Doppler device, the sensor consists of two transducers: one of them constantly emits ultrasound, the other constantly receives reflected signals. The receiver detects the Doppler shift, which is typically -1/1000 the frequency of the ultrasound source (audible range), and transmits the signal to the speakers and. parallel to the monitor for qualitative and quantitative assessment of the curve. Constant wave devices detect blood flow along almost the entire path of the ultrasound beam or. in other words, they have a large control volume. This may cause inadequate information to be obtained when multiple vessels enter the control volume. However, a large control volume can be useful in calculating the pressure drop in valvular stenosis. In order to assess blood flow in a specific area, it is necessary to place a control volume in the area of ​​interest (for example, inside a specific vessel) under visual control on a monitor screen. This can be achieved by using a pulse device. There is an upper limit to the Doppler shift that can be detected by pulsed instruments (sometimes called the Nyquist limit). It is approximately 1/2 of the pulse repetition rate. When it is exceeded, the Doppler spectrum is distorted (aliasing). The higher the pulse repetition frequency, the greater the Doppler shift can be determined without distortion, however, the lower the sensitivity of the device to low-speed flows.

Due to the fact that ultrasonic pulses sent into tissue contain a large number of frequencies in addition to the main one, and also due to the fact that the speeds of individual sections of the flow are not the same, the reflected pulse consists of a large number of different frequencies. Using the fast Fourier transform, the frequency content of the pulse can be represented in the form of a spectrum, which can be displayed on the monitor screen in the form of a curve, where the Doppler shift frequencies are plotted horizontally, and the amplitude of each component is plotted vertically. Using the Doppler spectrum, it is possible to determine a large number of speed parameters of blood flow (maximum speed, speed at the end of diastole, average speed, etc.), however, these indicators are angle-dependent and their accuracy is extremely dependent on the accuracy of angle correction. And if in large non-tortuous vessels correction of the angle does not cause problems, then in small tortuous vessels (tumor vessels) it is quite difficult to determine the direction of flow. To solve this problem, a number of almost angle-independent indexes have been proposed, the most common of which are the resistance index and the pulsator index. The resistance index is the ratio of the difference between the maximum and minimum speeds to the maximum flow rate. The pulsation index is the ratio of the difference between the maximum and minimum speeds to the average flow speed.

Obtaining a Doppler spectrum with a single reference volume allows blood flow to be assessed in a very small area. Color flow imaging (color Doppler mapping) provides real-time 2D information about blood flow in addition to conventional 2D greyscale imaging. Color Doppler imaging expands the capabilities of the pulsed principle of image acquisition. Signals reflected from motionless structures are recognized and presented in a grey-scale form. If the reflected signal has a frequency different from the emitted one, this means that it was reflected from a moving object. In this case, the Doppler shift is determined, its sign and the value of the average velocity. These parameters are used to determine color, saturation, and brightness. Typically, the direction of flow to the sensor is coded in red and that of the dispenser is coded in blue. The brightness of the color is determined by the flow speed.

To correctly interpret an ultrasound image, knowledge of the physical properties of sound that underlie the formation of artifacts is necessary.

An artifact in ultrasound diagnostics is the appearance of non-existent structures in the image, the absence of existing structures, incorrect location of structures, incorrect brightness of structures, incorrect outlines of structures, incorrect sizes of structures.

Reverberation, one of the most common artifacts, occurs when an ultrasonic pulse hits between two or more reflective surfaces. In this case, part of the ultrasonic pulse energy is repeatedly reflected from these surfaces, each time partially returning to the sensor at regular intervals. The result of this will be the appearance on the monitor screen of non-existent reflective surfaces, which will be located behind the second reflector at a distance equal to the distance between the first and second reflectors. It is sometimes possible to reduce reverberation by changing the position of the sensor.

An equally important artifact is the so-called distal acoustic shadow. An acoustic shadow artifact occurs behind highly reflective or highly absorbent structures. The mechanism of formation of an acoustic shadow is similar to the formation of an optical one.

Acoustic shadowing appears as an area of ​​decreased echogenicity (hypoechoic or anechoic = black) and is found behind highly reflective structures such as calcium-containing bone. Thus, the examination of the organs of the upper abdomen is hampered by the lower ribs, and the lower part of the pelvis is hampered by the symphysis pubis. This effect, however, can be used to identify calcified gallbladder stones, kidney stones and atherosclerotic plaques. A similar shadow can be caused by gas in the lungs or intestines.

The artifact of an echogenic “comet tail” is considered by a number of authors as a manifestation of an acoustic shadow. In turn, other sources indicate that this artifact is observed in the case when ultrasound causes the object’s own vibrations and is a variant of reverberation. It is often observed behind small gas bubbles or small metal objects. The echogenic “comet tail” artifact may prevent detection of structures located behind the bowel loops containing gas. The air artifact is an obstacle primarily in identifying organs located retroperitoneally (pancreas, kidneys, lymph nodes), behind the stomach or intestinal loops containing gas.

Due to the fact that not always the entire reflected signal returns to the sensor, an artifact of the effective reflective surface appears, which is smaller than the real reflective surface. Because of this artifact, the size of stones determined by ultrasound is usually slightly smaller than the true size. Refraction can cause an object to appear incorrectly in the resulting image. If the path of the ultrasound transducer to the reflective structure and back is not the same, an incorrect position of the object in the resulting image occurs.

The next characteristic manifestation is the so-called marginal shadow behind the cysts. It is observed mainly behind all the round cavities that hide sound waves along the tangent. The marginal shadow is caused by the scattering and refraction of the sound wave, and can be observed behind the gallbladder. This requires careful analysis to explain the origin of the acoustic shadow as an edge shadow effect caused by the gallbladder rather than a focal fatty liver.

The side shadow artifact is associated with refraction and, sometimes, interference of ultrasonic waves when the ultrasound beam falls tangentially onto a convex surface (cyst, cervical gallbladder) of a structure, the speed of ultrasound in which is significantly different from the surrounding tissue.

Artifacts associated with incorrect determination of ultrasound speed arise due to the fact that the actual speed of ultrasound propagation in a particular tissue is greater or less than the average (1.54 m/s) speed for which the device is programmed.

Ultrasound beam thickness artifacts are the appearance, mainly in fluid-containing organs, of wall reflections due to the fact that the ultrasound beam has a specific thickness and part of this beam can simultaneously form an image of the organ and an image of adjacent structures.

The artifact of distal pseudo-amplification of the signal occurs behind structures that weakly absorb ultrasound (liquid, liquid-containing formations). Relative distal acoustic amplification is found when a portion of the sound waves travel some distance through a homogeneous fluid. Due to the reduced level of reflection in the liquid, sound waves are attenuated less than those passing through adjacent tissues and have a greater amplitude. This produces distal increased echogenicity, which appears as a streak of increased brightness behind the gallbladder, bladder, or even behind large vessels such as the aorta. This increase in echogenicity is a physical phenomenon not related to the true properties of the underlying tissues. Acoustic enhancement, however, can be used to distinguish renal or hepatic cysts from hypoechoic tumors.

Quality control of ultrasonic equipment includes determining the relative sensitivity of the system, axial and lateral resolution, dead zone, correct operation of the distance meter, registration accuracy, correct operation of the VAG, determination of the dynamic range of the gray scale, etc. To control the quality of ultrasonic devices, special test objects or tissue-equivalent phantoms are used. They are commercially available, but are still not widespread in our country, which makes it almost impossible to carry out on-site verification of ultrasound diagnostic equipment.

Before considering the types and directions of ultrasound examination, it is necessary to understand and understand what the diagnostic effect of ultrasound is based on. The history of ultrasound goes back to 1881, when the Curie brothers discovered the “piezoelectric effect.” Ultrasound refers to sound vibrations that lie above the threshold of perception of the human hearing organ. The “piezoelectric effect,” which produces ultrasonic vibrations, found its first application during the First World War, when sonar was first developed and used to navigate ships, determine the distance to a target, and search for submarines. In 1929, ultrasound found its application in metallurgy to determine the quality of the resulting product (flaw detection). The first attempts to use ultrasound for medical diagnostic purposes led to the advent of one-dimensional echoencephalography in 1937. Only in the early fifties of the nineteenth century was it possible to obtain the first ultrasound image of human internal organs. Since then, ultrasound diagnostics has become widely used in the radiological diagnosis of many pathologies and injuries of internal organs. Subsequently, ultrasound diagnostics was constantly improved and expanded the scope of its application.

Types of ultrasound examination

Ultrasound examination has made a certain breakthrough in medicine, making it possible to quickly and safely, and most importantly, correctly diagnose and treat many pathologies. Currently, ultrasound examination is used in almost all areas of medicine. For example, using ultrasound of the abdominal cavity to determine the condition of internal organs, ultrasound and Doppler of blood vessels are used to diagnose many vascular diseases. The following types and directions of ultrasound examination are distinguished: A) Ultrasound examination with computer processing and color Doppler mapping (ultrasound of the thyroid gland, ultrasound of the liver, ultrasound of the mammary glands, ultrasound of the gall bladder, ultrasound of the pancreas, ultrasound of the bladder, ultrasound of the spleen, ultrasound of the kidneys, studies with vaginal and rectal sensors, ultrasound of the pelvic organs in women, ultrasound of the prostate in men); B) Ultrasound examination with Doppler sonography, color duplex scanning (ultrasound of the vessels of the brain and neck, lower extremities, joints and spine, ultrasound during pregnancy).

Ultrasound examinations create images of internal organs using high-frequency sound waves. Ultrasound examination is painless. Ultrasound examination is safe for pregnant women and children, as it does not involve radiation. To obtain ultrasound images, a gel is applied to the patient’s skin in the area where the examination will be carried out, and then the specialist moves the ultrasound sensor of the device over this area. The computer processes the received signal and displays it on the monitor screen in the form of a three-dimensional image.

Ultrasound of the thyroid gland

In examining the thyroid gland, ultrasound examination is the leading one and allows you to determine the presence of nodes, cysts, changes in the size and structure of the gland. As practice shows, due to the physical characteristics of the structure, not all organs can be reliably examined using the ultrasound method. For example, the hollow organs of the gastrointestinal tract are difficult to access due to the predominant gas content in them. However, ultrasound examination can be used to determine signs of intestinal obstruction and indirect signs of adhesions. Using an ultrasound of the thyroid gland, it is possible to detect the presence of free fluid in the abdominal cavity, if there is a lot of it, which can play a decisive role in the treatment tactics of a number of therapeutic and surgical diseases and injuries.

Ultrasound of the liver

Ultrasound examination of the liver is a fairly highly informative diagnostic method. The use of this type of examination allows the specialist to assess the size, structure and homogeneity, as well as the presence of focal changes and the state of blood flow. Ultrasound of the liver 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). The patient needs to know that any ultrasound findings of both the liver and other organs must be evaluated and considered only in conjunction with clinical, anamnestic data, as well as data from additional examinations. Only in this case will a specialist be able to reproduce the complete picture and make a correct and adequate diagnosis.

Ultrasound of the mammary glands (ultrasound mammography)

The main use of ultrasound examination in mammology is to clarify the nature of formations in the mammary gland. Ultrasound mammography is the most complete and effective examination of the mammary glands. Modern ultrasound examination of the mammary gland allows, with maximum detail, to equally effectively assess the condition of both superficial and deep tissues of the mammary gland of any size and structure. Due to the maximum detail of tissues, it is possible to bring the ultrasound anatomy of the mammary glands even closer to their morphological structure.

Ultrasound of the mammary glands is both an independent method for detecting benign and malignant formations in the mammary gland, and an additional one used in conjunction with mammography. In some cases, ultrasound examination is superior to mammography in its effectiveness. For example, when examining dense mammary glands in young women; in women with fibrocystic mastopathy; when cysts are detected. In addition, ultrasound of the mammary glands is used for dynamic monitoring of already identified benign breast formations, which makes it possible to identify dynamics and take adequate measures in a timely manner. Modern development of medical technologies has led to the fact that the ultrasound examination protocol includes not only an assessment of the condition of the mammary glands, but also regional lymph nodes (axillary, supraclavicular, subclavian, retrosternal, prothoracic). One of the components of an ultrasound examination is the assessment of blood flow in the mammary glands using a special technique - Dopplerography (spectral and color-coded - color Doppler mapping (CDC) and power Dopplerography), which is crucial in identifying malignant tumors of the mammary gland at the earliest stages of development.

Ultrasound of the gallbladder

Ultrasound of the gallbladder is an informative diagnostic method. To identify various pathologies of the gallbladder, specialists often use ultrasound examination. The gallbladder is responsible for storing and releasing bile produced by the liver. This process can be disrupted by many diseases to which the organ is susceptible: stones, polyps, cholecystitis and even cancer. The most common is dyskinesia of the gallbladder and biliary tract.

The purpose of an ultrasound examination is to determine the size, position, and examination of the walls of the gallbladder and the contents of the cavity. Echography of the gallbladder and bile ducts must be performed on an empty stomach, no earlier than 8–12 hours after a meal. This is necessary to sufficiently fill the bladder with bile. The patient is examined in three positions - on the back, on the left side, standing, at the height of a deep inspiration. Ultrasound of the gallbladder is completely safe and does not cause complications. Indications for an ultrasound scan of the gallbladder include clinical suspicion of gallbladder disease, including acute and palpable formation in the projection of the gallbladder, cardialgia of unknown nature, dynamic observation during conservative treatment of chronic cholecystitis, cholelithiasis, suspicion of a tumor of the gallbladder .

Ultrasound of the pancreas

An ultrasound examination of the pancreas allows the doctor to obtain additional information to make a diagnosis and prescribe the correct treatment. An ultrasound examination of the pancreas evaluates its size, shape, contours, homogeneity of the parenchyma, and the presence of formations. Unfortunately, high-quality ultrasound of the pancreas is often quite difficult, since it can be partially or completely blocked by gases in the stomach, small and large intestines. The most common conclusion made by ultrasound doctors is “diffuse changes in the pancreas” and may reflect both age-related changes (sclerotic, fatty infiltration) and possible changes due to chronic inflammatory processes. In any case, ultrasound examination of the pancreas is an integral stage of adequate treatment.

Ultrasound of the kidneys, adrenal glands and retroperitoneum

Carrying out an ultrasound examination of the retroperitoneum, kidneys and adrenal glands is a rather difficult procedure for an ultrasound specialist. This is primarily due to the peculiarities of the location of these organs, the complexity of their structure and versatility, as well as the ambiguity in the interpretation of the ultrasound picture of these organs. When examining the kidneys, their size, location, shape, contours and structure of the parenchyma and pyelocaliceal system are assessed. Ultrasound examination allows us to identify kidney abnormalities, the presence of stones, fluid and tumor formations, as well as changes due to chronic and acute pathological processes of the kidneys.

In recent years, methods of ultrasound diagnostics and treatment through puncture under ultrasound guidance have been widely developed. This section of ultrasound diagnostics has a great future, since it allows making an accurate morphological diagnosis. An additional advantage of performing therapeutic punctures under ultrasound guidance is that they are significantly less traumatic compared to conventional medical procedures. For example, the pathological area from which the material for research is taken is located deep in the body, therefore, without monitoring the progress of the biopsy using special imaging equipment, one cannot be sure that the material for research was taken from the right place. Ultrasound is used to monitor the progress of puncture biopsy. This method is highly informative and allows you to easily determine the position of the needle in the organ and be confident in the correctness of the biopsy. Without such control, biopsy of many organs is impossible.

In conclusion, it should be noted that the types and areas of ultrasound examination are so multifaceted and also applicable in a wide variety of areas of modern medicine that it is not possible to fully cover ultrasound diagnostics in one material. Today, ultrasound examination, due to its relatively low cost and wide availability, is a common method of examining a patient. Ultrasound diagnostics allows us to identify a fairly large number of diseases, such as cancer, chronic diffuse changes in organs. For example, 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, etc. Monitor your health, do not forget about preventive examination and you will save yourself from many problems in the future.

Ultrasound in medicine

Ultrasound diagnostic methods

4.2.1. Echography

4.2.2. Dopplerography

4.2.3. Image acquisition methods

The use of ultrasound diagnostic methods in practical medicine

4.3.1. Measuring blood flow speed

4.3.2. Ultrasound diagnosis of cerebral circulatory disorders

4.3.3. Echoencephalography

4.3.4. Ultrasound diagnostics of some internal organs

4.3.5. Ultrasound diagnostics in cardiology

4.3.6. Ultrasound diagnostics in pediatrics

4.3.7. Ultrasound diagnostics in gynecology and obstetrics

4.3.8. Ultrasound diagnostics in endocrinology

4.3.9. Ultrasound diagnostics in ophthalmology

4.3.10. Advantages and disadvantages of ultrasound diagnostics

Ultrasound in medicine

Ultrasound is extremely widely used in medical practice. It is used in diagnostics (encephalography, cardiography, osteodensitometry, etc.), treatment (crushing stones, phonophoresis, acupuncture, etc.), preparation of medicines, cleaning and sterilization of instruments and drugs.

Ultrasound is used in cardiology, surgery, dentistry, urology, obstetrics, gynecology, pediatrics, ophthalmology, abdominal pathology and other areas of medical practice.

Ultrasound diagnostic methods.

In ultrasound diagnostics, both the reflection of waves (echo) from stationary objects (the wave frequency does not change) and the reflection from moving objects (the wave frequency changes - the Doppler effect) are used.

Therefore, ultrasound diagnostic methods are divided into echographic and Dopplerographic.

Ultrasonic transillumination based on different absorption of ultrasound by different tissues of the body. When examining an internal organ, an ultrasonic wave of a certain intensity is directed into it and the intensity of the transmitted signal is recorded with a sensor located on the other side of the organ. Based on the degree of change in intensity, a picture of the internal structure of the organ is reproduced.

Echography

Echography - This is a method of studying the structure and function of organs and obtaining an image of a cross-section of organs corresponding to their actual size and condition.

In echography, a distinction is made between echolocation and ultrasound scanning.

Echolocation - This is a method for recording the intensity of the reflected signal (echo) from the phase boundary.

The general principles of the formation of echo signals from the boundaries of the tissues and organs being studied are similar to the well-known principles of radar and sonar. The object under study is irradiated with short ultrasonic pulses, the energy of which is concentrated along a narrow beam.

The pulse, propagating in the medium from the ultrasonic source, reaching the interface between media with different wave impedances Z, is reflected from the boundary and hits the ultrasonic receiver (sensor). The greater the difference in the wave impedances of these media, the greater the energy of the reflected pulse. Knowing the speed of propagation of the ultrasound pulse (in biological tissues, on average, 1540 m/s) and the time during which the pulse traveled the distance to the boundary of the media and back, we can calculate the distance d from the ultrasound source to this boundary:

This relationship underlies ultrasonic visualization of objects during echolocation.

Moving the sensor allows you to identify the size, shape and location of the object being examined.

In fact, the ultrasound speed varies for different tissues within +- 5%. Therefore, with an accuracy of 5% it is possible to determine the distance to the boundaries of the object and with an accuracy of 10% the extent of the object under study along the ray.

During echolocation, only short pulses are emitted. In medical ultrasound equipment, the ultrasound generator operates in pulse mode with a frequency of 2.5 - 4.5 MHz.

For example, echocardiography uses ultrasound pulses with a duration of about 1 microsecond. The sensor operates in emission mode less than 0.1% of the time, and the rest of the time (99.9%) in receive mode. In this case, the patient receives minimal doses of ultrasound radiation, ensuring a safe level of exposure to tissue.

Important advantages of echography include its non-ionizing nature and low intensity of energy used. The safety of the method is also determined by the brevity of the impact. As already noted, ultrasonic imagers operate in the radiation mode for only 0.1 -0.14 cycle times. In this regard, during a normal examination, the actual irradiation time is about 1 s. It is necessary to add to this that up to 50% of the energy of ultrasonic waves, attenuating, does not reach the object under study.

Ultrasound scanning

To obtain images of organs it is used ultrasound scanning.

Scanning is the movement of an ultrasonic beam directed at an object during examination. Scanning ensures registration of signals sequentially from different points of the object; the image appears on the monitor screen and is recorded in the device’s memory and can be reproduced on photographic paper or film. The image can be subjected to mathematical processing, measuring, in particular, the size of different elements of the object. The brightness of each point on the screen is directly dependent on the intensity of the echo signal. The image on the monitor screen is usually represented by 16 shades of gray or a color palette that reflects the acoustic structure of the fabrics.

In ultrasound diagnostics, three types of scanning are used: parallel (parallel propagation of ultrasonic waves), sectoral (propagation of ultrasonic waves in the form of a diverging beam) and complex (with movement or rocking of the sensor).

Parallel scanning

Parallel scanning is carried out using multicrystalline sensors that ensure parallel propagation of ultrasonic vibrations. When examining the abdominal organs, the search for the necessary anatomical landmarks is faster. This type of scanning provides vision of a wide field of view in the near zone and a high density of acoustic lines in the far zone.

Sector scanning

Sector scanning provides the advantage of a small area of ​​contact with the object when access to the area under study is limited (eyes, heart, brain through the fontanel). Sector scanning provides a wide field of view in the far field.

Convex sector scanning

Convex sector scanning, which is a type of sector scanning, differs in that the sensor crystals are arranged on a convex surface. This provides a wide field of view while maintaining a good field of view in the near field.

Complex scanning

Complex scanning is carried out when the sensor moves in a direction perpendicular to the line of propagation of the ultrasound beam. Since the sensor is in constant motion and the screen has a long afterglow, the reflected pulses merge, forming an image of a cross-section of the organ being examined at a given depth. For complex scanning, the sensor is fixed on a special tripod. In addition to moving the sensor along the surface, it is rocked at a certain angle around its axis. This ensures an increase in the amount of perceived reflected energy.

DOPPLEROGRAPHY

Doppler ultrasound is a diagnostic method based on the Doppler effect.

Doppler effect

In 1842, Christian Doppler, an Austrian physicist and astronomer, pointed out the existence of the effect that was later named after him.

The Doppler effect represents a change in the frequency of a wave emitted by a source when the source or receiver moves relative to the medium in which the wave propagates.

In Dopplerography, this is expressed in a change in the frequency of ultrasonic waves emitted by a stationary source when reflected from moving objects and received by a stationary receiver.

If the generator emits ultrasound with a frequency ע Г, and the object under study moves with a speed V, then the ultrasound frequency ע П recorded by the receiver (sensor) can be found by the formula:

where V is the speed of the body in the medium,

C is the speed of propagation of an ultrasonic wave in the medium.

The difference in the frequencies of the waves emitted by the generator and perceived by the receiver is called the Doppler frequency shift. In medical research, the Doppler frequency shift is calculated using the formula:

where V is the speed of movement of the object, C is the speed of propagation of ultrasound in the medium, ע Г is the initial frequency of the generator.

The frequency shift determines the speed of movement of the object under study.

Doppler methods use both continuous radiation and pulsed signals.

The radiation source and receiver operate simultaneously in continuous mode. The received signal is processed and the speed of the object is determined.

In pulse mode, one sensor is also used for emission and reception. It periodically works as an emitter for short periods of time, and in the intervals between emissions, as a receiver. Spatial resolution is achieved through the emission of short ultrasonic pulses.

Doppler sonography is effectively used in the diagnosis of blood flow and heart. In this case, the dependence of the change in the frequency of the incoming signal on the speed of movement of red blood cells or moving tissues of the heart is determined.

If the speed of the object v about is much less than the speed of the ultrasonic wave v knot, then the Doppler shift of frequency F relative to the frequency of the original wave f will be written in the form:

F= 2fcosθ v rev. /v knots

Here θ is the angle between the flow direction and the direction of the ultrasonic beam (Fig. 23).

Blood

Sensor

The doubling of the frequency shift results from the fact that objects first act as moving receivers and then as moving emitters.

It also follows from the above formula that if objects are moving towards the sensors, then F>0, if away from the sensors, then F<0.

If you measure F, then, knowing the angle θ, you can determine the speed of the object.

For example, if the ultrasound speed in the tissue is 1540 m/s, and the frequency of the ultrasound probe signal is 5-10 MHz, then the blood flow speed can be 1-100 cm/s, and the Doppler frequency shift will be 10 2 -10 4 Hz, t .e. Doppler frequency shift will appear in the audio frequency range.

The Doppler method is also used to study the great vessels of the head (transcranial Doppler).

Today, a lot is known about ultrasound diagnostics. The growing popularity of this method of studying the human body over the course of half a century has been facilitated by its proven safety and informativeness.

Despite the fact that most modern patients have a general understanding of ultrasound screening, many questions remain, the insufficient coverage of which causes a lot of discussion.

Perhaps we should start with what it is as such. Modern scientific medicine is constantly developing and does not stand still, which allows scientists to achieve different ways of studying the state of the body.

In any case, the search leads specialists to improve the diagnostic institute. Ultrasound is rightfully considered one of these discoveries. Trying to define the concept of “ultrasonic research”, first of all it is worth noting its non-invasiveness.

Carrying out an ultrasound examination of a person’s internal organs allows us to give the most objective assessment of their condition, functioning, confirm or refute suspicions of the development of pathological processes, and also monitor whether organs damaged in the past are restored during the prescribed treatment.

Meanwhile, it is worth noting that the ultrasound diagnostics industry continues to move forward with confident steps, opening up new opportunities for affordable detection of diseases.

How ultrasound is used during examination: principle of operation

The process of identifying pathologies occurs due to the perception of high-frequency signals. Ultrasonic waves, or, if you can call them that, signals, are fed through the equipment sensor to the object being examined, which results in a display on the device’s screen.

For ideally tight contact with the surface under study, a special gel is applied to the human skin, allowing the sensor to slide and preventing air from entering between it and the area under study.

The clarity of the image largely depends on the reflectance of the internal organ, which varies due to its heterogeneous density and structure. This is why ultrasound examination is not carried out when diagnosing the lungs: the complete reflection of supersonic signals by the air present in the lungs prevents the receipt of any reliable information about the lung tissue.

Moreover, the higher the density level of the examined organ area, the higher the resistance to reflection. As a result, darkened or lighter images appear on the monitor. The first version of the image is more common; in the second case, they speak of the presence of stones. A lighter image can be observed during bone tissue diagnostics.

Different tissues have different degrees of permeability to the echo signal. This is what ensures the operation of such a device.

What organs can be examined?

The demand for this diagnostic procedure can easily be explained by its versatility.

Ultrasound screening allows you to obtain objective data on the condition of the most important human organs and systems:

• brain;
• lymph nodes, internal sinuses;
• eyes;
• thyroid gland;
• cardiovascular system;
• abdominal organs;
• pelvic organs;
• liver;
• urinary system.

Despite the fact that it is possible to examine the brain using ultrasound only in childhood, this examination method is also applicable to the vessels of the neck and head.

This diagnostic procedure allows you to get a detailed understanding of blood flow and disruptions in the functioning of blood vessels that supply nutrition to the brain. Screening is also carried out if there is a suspicion of diseases of the endocrine system, as well as sinusitis, inflammatory processes in the maxillary and frontal sinuses in order to detect pus in them.

Using a special sensor, the diagnostician is able to assess the condition of the vessels of the fundus, vitreous body, optic nerve, and obtain information about the blood supply of the arteries. One of the organs that has the most convenient surface location for ultrasound diagnostics is the thyroid gland. All that interests the specialist during the examination is the size of the gland’s lobes, the presence of benign nodules, and the state of lymphatic drainage.

When screening the heart and blood vessels, it is important to study the condition of blood vessels, valves and arteries, identify aneurysms and stenoses, as well as detect deep vessel thrombosis, myocardial functionality, and ventricular volume.

At the moment, this method of examining the body is widely used in medicine, allowing one to examine any structure of the body absolutely painlessly.

Other organs for ultrasound examination

Using ultrasound, the organs of the abdominal cavity, pelvis, and liver are also examined. Thanks to diagnostics, it has become possible to timely detect inflammatory processes, stone formations and their dimensions, and the presence of neoplasms (their malignancy or benignity cannot be determined using ultrasound).

Ultrasound diagnostics of the female body deserves special attention. The importance of the ultrasound examination method is difficult to overestimate, since it is used as an alternative procedure to mammography and radiography. However, in some cases, ultrasound is not able to see salt deposits (calcifications) in the mammary glands, which often indicate the presence of a tumor.

Ultrasound can determine whether there are any neoplasms (cysts, fibroids, fibroids, cancerous tumors) within the uterus or ovaries.

To objectively assess the condition of these organs, the study is most often carried out with a full bladder (transabdominal route), but sometimes transvaginal diagnostics are also used, usually on a certain day of the menstrual cycle.

How is the procedure done?

Probably, most modern patients who periodically seek medical help know how to undergo the study. In order to obtain the necessary information about the state of the objects being examined, it is important to ensure the penetration of microwave pulses.

Before starting the ultrasound procedure, the doctor adjusts the equipment in accordance with the settings used for the screening procedure of various organs, since the tissues of the human body absorb or reflect ultrasound to varying degrees.

Thus, during the procedure, insignificant heating of the tissue occurs. This does not cause any harm to the human body, since the heating process occurs over a limited period, without having time to affect the general condition of the patient and his sensations. Screening is carried out using a special scanner and a high-frequency wave sensor.

The latter emits waves, after which ultrasound is reflected or absorbed from the areas under study, and the receiver receives the incoming waves and sends them to the computer, as a result they are transformed using a special program and displayed on the screen in real time.

The process of carrying out such a procedure is quite simple and absolutely painless, and no specific preparatory measures are required on the part of the patient.

How should a patient behave during the study?

Ultrasound diagnostics is a procedure that occurs as follows:

• The patient provides access to the device to the tissue area being examined.
• During the examination, the patient lies motionless, but at the request of the doctor he can change position.
• Screening begins from the moment the special sensor comes into contact with the surface of the area under study. The doctor should lightly press it against the skin, having previously lubricated the surface being examined with a gel-like substance.
• The duration of the procedure in rare cases exceeds 15–20 minutes.
• The final stage of screening is the doctor drawing up a final conclusion, the results of which should be deciphered by the attending physician.

Unlike conventional procedures, some gynecological examinations are performed using a special probe that has an elongated shape because it is inserted through the vagina. Any painful sensations during the procedure are excluded.

Echogenicity, hypoechogenicity and hyperechogenicity: what does it mean?

As a rule, ultrasound screening is a procedure whose principle is echolocation.

As already mentioned, this is the property of organ tissues to reflect the ultrasound arriving at them, which during diagnosis is noticeable to a specialist as a black and white image on the screen. Because each organ is reflected differently (due to its structure, fluid in it, etc.), it appears in a specific color on the monitor. For example, dense tissues are displayed in white, and liquids are displayed in black.

A doctor specializing in ultrasound research knows what echogenicity should normally be in each organ. If the indicators deviate upward or downward, the doctor makes a diagnosis. Healthy tissues are visible in gray, and in this case they speak of isoechoicity.

With hypoechogenicity, i.e. As the norm decreases, the color of the picture becomes darker. Increased echogenicity is called hyperechogenicity. For example, kidney stones are hyperechoic, and the ultrasound wave cannot pass through them.

Hypoechogenicity is not a disease, but an area of ​​high density, most often a calcified mass formed by fat, bone formation or stone deposition

In this case, only the upper part of the stone or its shadow is visible to the doctor on the screen. Hypoechogenicity indicates the development of swelling in the tissues. In this case, a full bladder is reflected on the screen in black, and this is a normal indicator.

An important point is that a specialist’s note about increased echogenicity should be a cause for serious concern. In some cases, this sign indicates the development of an inflammatory process and the appearance of a tumor.

Reasons for errors

Absolutely all specialists involved in the field of screening diagnostics are aware of the impressive number of so-called artifacts that are often encountered during the procedure.

It is not always possible to accurately recognize certain signs of an ultrasound examination, which can be blamed on:

• physical limitations of the technique;
• the occurrence of acoustic effects during the influence of ultrasound on the tissue of the organ under study;
• errors in the methodological plan for conducting the survey;

incorrect interpretation of screening results.

Artifacts encountered during the procedure

The most common artifacts that can affect the conclusion and progress of a study are:

Acoustic shadow

It is formed from stone formations, bones, air bubbles, connective tissue and dense formations.

Significant reflection of sound from the stone leads to the fact that the sound does not propagate behind it, and in the photographs this effect looks like a shadow

Wide Beam Artifact

When a gallbladder or cystic formation appears on the screen, a kind of dense sediment becomes visually noticeable and a double contour appears. The reason for such inaccurate data display is considered to be errors in the technical serviceability of the sensors. It can be avoided by conducting research in two projections.

"Tail of the Comet"

The phenomenon can be visualized when ultrasound passes through neoplasms that have a highly reflective surface. Most often, this artifact has a clear meaning and entails a specific diagnosis, speaking about the formation of calcifications, gallstones, gas, as well as when air gets between the device and the epidermis (due to an unstable fit).

Most often, this phenomenon is observed when scanning small calcifications, small gallstones, gas bubbles, metallic bodies, etc.

Speed ​​Artifact

It is worth taking it into account when processing the resulting image, since the speed of sound is constant, which allows you to calculate the return time of the signal and determine the distance to the object under study.

Mirror image

The appearance of false structures or neoplasms can be explained by multiple reflections of ultrasound when passing through dense objects (liver, blood vessels, diaphragm). This artifact occurs especially often when scanning an organ that has a medium with energy that is designed to slightly absorb waves.

This artifact may be a marker of possible pathologies in which the density of soft tissues increases

Comparison of ultrasound with other types of examination

In addition to ultrasound examination, there are other, no less informative diagnostic methods.

Among the hardware methods for examining the patient’s body, which are in no way inferior in the frequency of use of ultrasound, are:

• radiography;
• magnetic resonance imaging;
• computed tomography.

However, it is impossible to single out the most effective one. Each of them has its pros and cons, but often one diagnostic method complements the other, allowing doctors to sum up the suspicions of doctors when the clinical picture is not clearly expressed.

When comparing ultrasound screening with MRI, it is worth noting that the latter type of diagnostic device is a powerful magnet that has a direct effect on the patient’s body thanks to electromagnetic waves. In this case, an ultrasound examination is a procedure during which ultrasonic waves of minimal power penetrate through internal organs with varying degrees of density.

This type of diagnosis is much more often used for diseases of the abdominal organs, including the liver, gallbladder, pancreas, urinary tract and kidneys, glands of the endocrine system, vessels of the neck and head.

Differences between ultrasound screening, x-ray and CT

However, ultrasound is powerless in examining the lungs and bone apparatus. This is where radiography comes to the rescue. Despite the availability of ultrasound screening, the procedure does not pose any danger to the patient.

Unlike radiography, which is used when it is necessary to examine bones, ultrasound can only image soft and cartilage tissue. In addition, ultrasound screening does not have such negative side effects in the form of ionizing radiation. When choosing between the use of ultrasound and CT for suspected diseases of the brain, lungs and bone tissue, specialists, in the absence of contraindications, give priority to the latter.

Together with a contrast agent, doctors are often able to achieve high-quality images that contain more informative details. In this case, CT produces radiation and in some cases may be contraindicated. If it is necessary to carry out repeated diagnostic procedures in order to minimize the risk of radiation, the choice is an ultrasound examination.

All of the above diagnostic methods are highly informative. The examination is selected on an individual basis, depending on the screening algorithm and the patient’s clinical picture. Ultrasound diagnostics, like other research methods, has its advantages and disadvantages, so the procedure is strictly determined by the indications.