2 Edition

An object in motion changes its wave frequency. When the blood cell strives TO to the emitter - the reflected frequency is higher, FROM emitter - the reflected frequency is lower.

The source and receiver of the ultrasound wave are located in the sensor. The device measures the Doppler frequency shift: ΔF=(Fd-Fo), where Fd is the sensor frequency, Fo is the reflected frequency.

Click on pictures to enlarge.

The ultrasonic wave falls on the velocity vector under ∠α. ΔF is determined by the projection of the velocity vector onto the ultrasound beam (V·cosα): ΔF=2Fд·V·cosα/C, C is the speed of sound in soft tissues 1540 m/s.

To estimate the blood flow velocity, the Doppler equation is used: V=ΔF·C/2Fd·cosα. When the ultrasound beam penetrates the vessel at ∠90° ⇒ cosα=0, it is impossible to estimate the blood flow velocity.

For ∠0-60° the cosα value is from 1 to 0.5; for ∠60-90° the cosα value is from 0.5 to 0. Shortly from 90° the Vcosα value is small ⇒ ΔF small ⇒ speed inaccurate.

When ∠α is below 25°, the ultrasound beam is almost completely reflected from the vessel wall. To determine the flow speed, direct the ultrasound beam at an angle of 25-60°.

Duplex and triplex scanning of blood vessels

Three levels of vascular ultrasound: gray scale (B-mode), color Doppler mapping (CDC) and spectral Doppler (D-mode).

Duplex scanning of vessels - B-mode and Color Doppler, B-mode and D-mode; triplex scanning of vessels - B-mode, Color Doppler and D-mode.

The CDC encodes speed and direction into shades of red and blue: dark and light tones—low and high speeds. When the speed goes off scale, the purity of the colors disappears.

Iridescence (eleasing) indicates high-velocity flow at the site of stenosis. Adjust the speed scale: 4 cm/s - low, 115 cm/s - high, 39 cm/s - correct.

Power Doppler encodes speed, but not direction, into shades of the same color; useful in tortuous vessels and at low speeds.

Task.

The spectrum is obtained from a gate in the center of the vessel. The vertical axis is the speed scale; horizontal - time; baseline trims the flow TO And FROM sensor

The spectrum may cross the baseline; the components on opposite sides are called phases. The spectrum can be mono-, bi-, three- and four-phase.

How to measure blood flow speed

1. Place the gate in the center of the vessel (trackball), set the length to 2/3-4/5 of the lumen (SVlength);

2. The angle between the ultrasound beam and the axis of the vessel is 25-60°, the cursor is along the flow;

3. The spectrum occupies 2/3-4/5 of the speed scale (PRF), time base for 2-3 cycles;

4. For arteries, the spectrum is placed above the baseline, for veins - below (Invert).

5. Adjust the gain (GAIN) so that the spectrum outline is clear.

6. Circle the spectrum and get a report - Vps, Ved, RI, PI, etc.

Task. Ultrasonic beam and vessel at ∠90° (1) - the spectrum is unclear; correct the tilt of the sensor (2) - PSV 43.3 cm/sec; italics along the flow (3) - correct PSV 86.6 cm/sec. RI and PI do not require angle correction.

Quantitative characteristics of the spectrum

Vps— peak systolic velocity;

Ved— maximum end-diastolic velocity;

TAMX— time-averaged maximum blood flow velocity;

TAV— time-averaged average blood flow velocity;

R.I.=(Vps-Ved)/Vps - the resistivity index reflects the resistance to flow beyond the measurement location;

P.I.=(Vps-Ved)/TAMX - pulsatility index reflects the elastic properties of the arteries;

In the portal vein P.I.=PSV/EDV;

PI'=(Vps-Ved)/TAV—modified pulsatility index;

SBI=(Vps-TAV)/Vps=1-TAV/Vps - spectral expansion index reflects the flow turbulence;

SBI'=(Vps-TAV)/TAMX—modified spectral expansion index;

S/D- systolic-diastolic ratio;

AT— acceleration time;

A.I.— acceleration index.

Task. Measurement of peak systolic, maximum end-diastolic velocity, TAMX, TAV for high and low resistance arteries.

PSV and EDV are high at the site of stenosis; RI rises before and falls after stenosis. After stenosis, the spectrum has a tardus-parvus shape: PSV late - TPT>70 ms, PSV/TTP<5 м/с²; маленький — PSV и RI.

Qualitative characteristics of the spectrum

Antegrade flow is correct relative to the circulatory system - TO heart in veins, FROM hearts in arteries. Retrograde flow is contrary to natural flow.

For colorectal circulation, it is customary to paint veins blue and arteries red. The spectrum is drawn below the baseline for veins, above the baseline for arteries.

Antegrade flow of the hepatic vein TO heart - blue vessel, spectrum below the baseline; hepatic artery FROM heart - the vessel is red, the spectrum is above the baseline.

Speed ​​changes can be repeated at regular intervals. Such a flow is cyclical, the spectrum has ascending and descending segments.

Each cycle has an even number of bends, otherwise it will never repeat. Each bend in the spectrum generates an audio signal.

The spectrum in the veins is phase - soft waves; pulsating in the arteries - sudden changes; phaseless flow at constant speed.

In the spectrum, fast red blood cells with large ΔF are closer to the envelope; slow red blood cells with small ΔF are closer to the baseline.

The speed is higher in the center of the vessel, lower near the wall. When a large spread of speeds enters the gate, there is a broadening of the spectrum.

In the aorta, the gate passes a uniformly moving column of blood cells - a spectrum without broadening, a large spectral window.

In small vessels with laminar flow and turbulence, the broadening of the spectrum completely closes the spectral window.

In vessels with high resistance at the end of diastole, the flow is weak, RI>0.7; in vessels with low resistance in diastole the flow is significant, RI 0.55-0.7.

Vessels with high resistance: the external carotid and arteries of the extremities, as well as the superior and inferior mesenteric arteries in a hungry person.

Vessels with low resistance: internal carotid, renal, hepatic, testicular arteries, as well as mesenteric arteries in a well-fed person.

Normal spectrum shape in vessels

Abnormal spectrum shape in vessels

Take care of yourself, Your Diagnosticer!

Year of issue: 1999

Genre: Obstetrics, diagnostics

Format: PDF

Quality: Scanned pages

Description: The last decade has been marked by the widespread introduction of ultrasound diagnostics into obstetric practice, and today we can confidently say that echography has become an integral screening component of prenatal examination. In recent years, the Russian Association of Ultrasound Diagnostics in Perinatology and Gynecology has published books covering the basics of ultrasound diagnostics in obstetrics, gynecology and pediatrics. These books have become tabletop books. Numerous positive responses received by the editors are clear evidence that they provide significant assistance to specialists in their difficult daily work. The editorial board expresses deep gratitude to everyone who sent their wishes for the release of new books. The main wish is a detailed description of new research methods that are currently being introduced into obstetric practice. This primarily applies to Doppler ultrasound.
The guide “Dopplerography in Obstetrics” opens a new series of books, which we called “Encyclopedia of Ultrasound Diagnostics in Obstetrics and Gynecology.” Encyclopedia translated from Greek (enkyklios paideia) means training in the entire range of knowledge. The task of our encyclopedia is to systematize knowledge on specific sections of ultrasound diagnostics in perinatology and gynecology. In the near future, it is planned to publish guidelines on Doppler ultrasound in gynecology, prenatal diagnosis of congenital malformations and fetal echocardiography.
The field of ultrasound diagnostics in perinatology and gynecology is rapidly expanding and is rapidly updated with new data. For a more complete coverage of modern provisions, we invited leading domestic and foreign scientists to join the team of authors, who kindly agreed to provide us with the results of their latest work. The Editorial Board expresses its sincere gratitude to Professor Azim Kurjak and his colleagues (Croatia) and Gregory DeVore (USA) for preparing special chapters for this manual on Doppler ultrasound in obstetrics.
The guide “Dopplerography in Obstetrics” widely presents modern aspects of the use of Dopplerography in obstetric practice. The book opens with a chapter on the safety of Doppler examinations during pregnancy. It discusses in detail modern views on this problem. It should be emphasized that to ensure maximum safety of Doppler examinations, the rules presented in this chapter must be strictly followed. The following chapters highlight the methodology, normative values ​​and diagnostic capabilities of Doppler studies of uteroplacental and fetal blood flow in complicated pregnancy. A separate chapter is devoted to a discussion of clinical and diagnostic issues of the critical state of fetal-placental blood flow based on a summary analysis of world literature data on this pathology.
A new page in Doppler research in obstetrics is the study of intraplacental blood flow, which made it possible to formulate a modern concept of the relationship between the uteroplacental and fetal-placental circulation. In the chapter devoted to this issue, new diagnostic criteria for assessing disturbances of intraplacental blood flow in early pregnancy are presented for the first time.
Particular attention is paid to fetal Doppler echocardiography. This method is just beginning to be introduced in our country, although its high diagnostic and prognostic value for various fetal diseases and especially congenital heart defects is beyond doubt. A special chapter presents the technology of Doppler echocardiographic examination of the fetus, normative indicators of intracardiac hemodynamics and diagnostic criteria for its disorders.
The chapter devoted to the use of Doppler ultrasound for extracardiac anomalies in the fetus summarizes the world experience of using this method in the differential prenatal diagnosis of aneurysm of the vein of Galen, congenital malformations of the lungs and abdominal organs, renal agenesis, superficial hemangiomas, pathology of the umbilical cord and placenta. In the last chapter of this manual, a leading specialist from the largest scientific center in our country expresses his opinion on the use of Doppler ultrasound in the diagnosis of trophoblastic disease.
In conclusion, I would like to express the hope that this book will help improve ultrasound diagnostics in obstetrics in our country. The team of authors will be grateful for your wishes, which we will try to take into account in subsequent editions of the encyclopedia.

"Dopplerography in obstetrics"

1. Contemporary assessment of the safety of Doppler studies
2. Uteroplacental blood flow
3. Arterial fetal-placental blood flow
4. Critical condition of fetal-placental blood flow
5. Study of blood flow in the veins of the fetus
6. Intraplacental blood flow
7. Doppler echocardiography of the fetus in the second half of pregnancy
8. The use of Doppler ultrasound for extracardiac anomalies in the fetus
9. Trophoblastic disease

type of service: Diagnostic, service category: Ultrasonic

Clinics in St. Petersburg where this service is provided for adults (176)

Clinics in St. Petersburg where this service is provided for children (68)

Specialists providing this service (1)

Doppler ultrasound- one of the ultrasound methods of examining the body, based on the Doppler effect, discovered by the author back in 1842.

Operating principle of Doppler ultrasound devices

The essence of the Doppler effect is that ultrasonic waves are reflected from moving objects with a frequency shift, which is proportional to the speed of movement of the object under study, and if the movement is directed towards the sensor, the frequency increases, if away from the sensor, it decreases.

Although the technique allows you to obtain information about the movement of any liquid media, in modern medicine Dopplerography is used primarily to study the vascular bed and blood flow in it. Modern ultrasound diagnostic devices to record the Doppler effect use a transmitter that sends ultrasonic waves in the direction of the vessel being examined, and a receiver that records the change in the frequency of the received ultrasound signal when it is reflected from moving blood particles (primarily from red blood cells). The data obtained make it possible to obtain the main characteristics of blood flow in the vessel under study: the speed and direction of blood movement, the volume of blood mass moving at certain speeds. Based on these characteristics, certain conclusions can be drawn about blood flow disturbances, the condition of the vascular wall, the presence of atherosclerotic stenosis or blockage of blood vessels with blood clots, etc.

Classification of Doppler ultrasound methods

There are several main Doppler sonography methods:

Flow spectral dopplerography (PSD)

continuous

pulse

Power Doppler (ED)

Spectral Dopplerography (PSD) used to assess blood flow in relatively large vessels and chambers of the heart (echocardiography). The data obtained from PSD are similar to a cardiogram or a picture on the oscilloscope screen, and represent a graph of blood flow velocity over a certain time (the vertical axis reflects the speed, and the horizontal axis shows time). In this case, the signals displayed above the horizontal axis come from the blood flow directed to the sensor, below this axis - from the sensor. Continuous PSD records the movement of blood to the entire depth of penetration of the ultrasonic wave, while pulsed PSD allows recording only blood flow at a given distance from the sensor.

Power Doppler (ED), unlike PSD, allows you to display blood flow in all vessels in the area of ​​the body being studied, including small vessels with a very low blood flow rate. But at the same time, ED does not allow one to assess the direction, nature and speed of blood movement. Therefore, ED is mainly used to assess vascularization (adequacy of blood supply) of internal organs and individual areas of soft tissue. The data obtained during ED is displayed on the device monitor in the form of a color image of the organ being examined or a section of soft tissue, while shades of color (usually from dark orange to yellow) carry information about the intensity of the echo signal, and, accordingly, the quality of the blood supply.

Modern ultrasound machines make it easy to combine the above methods.

Isolated Doppler ultrasound is rarely used today. The so-called duplex scanning(duplex Doppler ultrasound), which is a combination of Doppler ultrasound scanning (in PSD or ED mode) with traditional ultrasound examination. The traditional mode of ultrasound, the so-called B-mode, provides information in the form of two-dimensional black and white images of anatomical structures in real time. Its use in Dopplerography makes it possible to more accurately localize the vessel under study and obtain information about the structure of its wall, the size of the lumen, etc.

The remaining options for vascular Dopplerography do not differ fundamentally from those described above, and are additions based on computer processing of the data obtained during the study:

color Doppler mapping (color Dopplerography)

triplex scanning

three-dimensional dopplerography

Color mapping allows you to display information about the characteristics of blood flow in a form more convenient for interpretation - when on the device monitor, depending on the direction of blood flow, its image is colored red or blue, the shades of which depend on the speed of blood flow.

Triplex scanning often called duplex Doppler with color mapping.

Finally, three-dimensional dopplerography allows, using computer modeling, to construct a three-dimensional image of the organ or vessel being studied, and to monitor the blood flow in it in real time (with color mapping). To build a three-dimensional model, a series of images of the research object from different angles in manual mode is required, which carries with it the main disadvantage of the method - a high probability of geometric distortions due to uneven manual movement of the sensor.

The lecture for doctors addressed the following issues:

Types of Doppler examination

• 1. Color Doppler coding (CDC, Cl, CFI) and power Doppler (PD - power doppler)
• 2. Spectral Dopplerography
  • constant wave (CW - constant wave)
  • pulsed wave (PW)
• 3. Tissue Dopplerography
• Spectral Dopplerography - designed to assess the movement of moving media - blood flow in the vessels and chambers of the heart, the walls of the heart. The main type of diagnostic information is a spectrographic record, which is a sweep of the blood flow velocity over time - the blood flow velocity curve (BSV). On such a graph, speed is plotted along the vertical axis, and time is plotted along the horizontal axis. Signals displayed above the horizontal axis are recorded from the blood flow directed towards the sensor, below this axis - from the sensor. In addition to the speed and direction of blood flow, the type of Doppler curve can determine the nature of blood flow:
  • laminar flow (displayed as a narrow curve with clear contours)
  • turbulent - (wide non-uniform curve)

• Quantitative linear parameters of blood flow peak systolic blood flow velocity (Vps; PSS)
  • end-diastolic blood flow velocity (Ved; EDP)
  • time-averaged maximum blood flow velocity (TAMX - time average maximum velocity) is the result of averaging the speed components of the Doppler spectrum envelope over one or several cardiac cycles;
  • time-averaged average velocity of blood flow (TAV - time average velocity) is the result of averaging the components of the spectral distribution over one or more cardiac cycles
  • peripheral resistance index (Pourcelot) - RI
  • pulsation index (Gosling) - PI
  • systole-diastolic ratio (S/D)
  • acceleration time (AT)
• Resistance index. The peripheral resistance index (Pourcelot, RI - resistive index) indirectly characterizes the state of peripheral resistance in the studied vascular area. The value of the index in arteries with low peripheral resistance is equal to the ratio of the difference between the peak systolic and maximum end-diastolic blood flow velocity to the peak systolic blood flow velocity

• The pulsatility index (Gosling, PI - pulsatility index) indirectly characterizes the state of peripheral resistance in the vascular area under study. The value of the index in arteries with low peripheral resistance is equal to the ratio of the difference between peak systolic and maximum end-diastolic blood flow velocity to the time-averaged maximum blood flow velocity

• Acceleration time (Tass). The length of time spent to achieve peak systolic velocity (PSV, Vps) from the moment of reaching end-dystolic velocity (EDV, Ved)

View and buy books on ultrasound by Medvedev:

Medical literature to improve professional level

The methodological manual contains a set of brief and clearly formulated proposals for the non-invasive diagnosis of arterial pathology of the lower extremities. The presented method of comprehensive ultrasound examination, based on the use of the diagnostic advantages of Doppler ultrasound and duplex scanning with color mapping of blood flow, was developed on the basis of the department of surgical treatment of arterial pathology

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All aspects of the ultrasound screening protocol in the second trimester of pregnancy are discussed in detail. Particular attention is paid to ultrasound fetometry, assessment of the placenta, amniotic fluid and umbilical cord. The issues of ultrasound anatomy of the fetus in the second trimester of pregnancy with normal development and various congenital defects are presented in detail. A separate chapter is devoted to echographic markers of chromosomal abnormalities in the fetus.

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The subject of the book covers almost all aspects of the use of Doppler ultrasound examinations, such as ultrasound examination of cerebral vessels, arteries and veins of the upper and lower extremities, abdominal and pelvic vessels in men and women. Among domestic publications there are no analogues to this book in terms of the volume of information contained.

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Fundamental provisions for conducting a screening study at 30-34 weeks of pregnancy. All aspects of the ultrasound screening protocol in the third trimester of pregnancy are discussed in detail. Particular attention is paid to ultrasound fetometry

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The manual analyzes the influence of pathophysiological processes on the Doppler spectrum of arterial blood flow. The necessity of knowledge of hemodynamic principles for specialists in ultrasound diagnostics is shown, regardless of their narrow profile specialization. Examples are given of how the skillful application of these principles in the analysis of Doppler frequency shift spectrum curves significantly helps to draw the right conclusion and make the only correct decision in making a diagnosis. The possibilities of applying hemodynamic principles in the most common clinical situations are shown.

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The manual outlines the principles and methodology of complex ultrasound diagnostics of the pathology of extra- and intracranial vessels, vessels of the upper and lower extremities. The criteria for the hemodynamic significance of damage to the brachiocephalic vessels and the requirements for their study are considered. Much attention is paid to the problems of venous pressure and functional phlebohypertension.

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The book discusses the features of embryogenesis, anatomy and hemodynamics of the fetal cardiovascular system in normal conditions and in various congenital cardiac pathologies. The capabilities of ultrasound techniques in the prenatal diagnosis of congenital heart defects and heart rhythm disturbances in the fetus at different stages of pregnancy are reflected in detail.

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Almost all methods for studying the internal organs of a child are collected with large digital material, tables, and diagrams. For a better understanding of the material, examples of pathological changes are sometimes given. For the first time, data is provided on some issues that were not touched upon in the textbook - the thymus gland, large vessels of the abdomen, emergency medicine.

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Ultrasound reference book with a detailed description of the sizes and volumes of organs, diameters of blood vessels (arteries and veins) in adults and children.

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The manual clearly and logically describes the method of ultrasound examination of the arterial and venous systems, the use of technical techniques and their diagnostic value. For ultrasound diagnostic doctors, it will also be useful for specialists working in the field of vascular and X-ray endovascular surgery.

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Planimetric (dimensional) and quantitative indicators of internal organs during ultrasound examinations in children and adults are systematized. Quantitative indicators of normal intravascular hemodynamics of arteries of various basins are given. Quantitative and hemodynamic parameters are presented during ultrasound examination of the heart in both children and adults.

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The issues of optimizing the image of the heart and main arteries in gray scale mode and color Doppler mapping mode are considered in detail. The methodology for screening echocardiographic examination of the fetus and the echographic signs of various congenital heart defects are presented in detail.

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The protocol for ultrasound examination at 11–14 weeks of pregnancy is discussed in detail. Particular attention is paid to the rules of prenatal echographic markers of chromosomal abnormalities. Detailed information on ultrasound anatomy for normal fetal development and various congenital defects is provided.

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Rules for measuring each fetometric indicator of the biometry of the internal organs of the fetus. Particular attention is paid to schematic images and echograms that clearly demonstrate the rules for determining fetometric and biometric indicators of internal organs and various structures of the fetus.

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Basics of Doppler studies of uteroplacental blood flow and blood flow in various fetal vessels at different stages of pregnancy. The indications and methods of Doppler ultrasound in obstetric practice are considered in detail. Particular attention is paid to the use of Doppler ultrasound in placental insufficiency.

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Detailed data are provided on the capabilities of new ultrasound technologies, including volumetric echography, for various congenital and hereditary diseases. The fourth edition has been supplemented with a new chapter, which examines modern aspects of ultrasound assessment of the placenta, umbilical cord and amniotic fluid.

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The issues of methodology for conducting volumetric echography in the study of various organs and structures of the fetus, depending on the stage of pregnancy, are discussed in detail. Particular attention is paid to the use of volumetric echography in the assessment of facial structures, brain, skeleton, limbs and heart of the fetus.

CLINICAL STANDARDS COMMITTEE

The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) is a scientific organization that promotes clinical practice in ultrasound, training and research in diagnostic imaging in women's health.

The ISUOG Clinical Standards Committee (CSC) was created to develop Practice Guidelines and Consensus Statements as educational recommendations that provide healthcare professionals with a common approach to diagnostic imaging.

They are intended to reflect provisions reviewed by ISUOG and considered best practice at the time of publication. Although every effort has been made by ISUOG to ensure the accuracy of the text of the manual in its publication, however, neither the Society itself nor any of its employees or members accepts legal liability for the consequences of any inaccurate or misleading information, options or statements published by the CSC.

ISUOG guidelines do not purport to set legal standards in health care because the interpretation of the evidence contained in the guidelines may be influenced by individual circumstances and the availability of resources. Approved manuals may be freely distributed with permission from ISUOG ( [email protected]).

This document summarizes practical recommendations on how to perform Doppler ultrasound of the fetoplacental circulation. Of particular importance is the provision that the embryo and fetus should not be exposed to unnecessary harmful effects of ultrasound energy, especially in the early stages of pregnancy.

At these stages, Doppler ultrasonography should be performed when clinically indicated and using the lowest energy levels possible. ISUOG previously published guidelines for the use of Doppler ultrasound for fetal ultrasound examinations from 11 to 13+6 weeks of gestation (1).

When performing Doppler scanning, thermal index (TI) readings should not exceed 1 and exposure time should be kept to a minimum, usually no longer than 5–10 minutes and a maximum of 60 minutes (1). It is not the purpose of this guideline to define clinical indications, specify specific periods of pregnancy at which Doppler ultrasonography should be performed, discuss how diagnostic findings should be interpreted, or discuss the use of Doppler ultrasonography during fetal echocardiographic examinations.

The purpose of the manual is to describe pulsed wave Doppler ultrasound and its various modes such as spectral, color and energy, which are traditionally used in studies of blood circulation in the mother-placenta-fetus system. We will not describe the continuous wave Doppler method, since it is not usually used in obstetric ultrasound.

However, in cases where the fetus develops conditions that lead to very high flow rates (eg, aortic stenosis or tricuspid regurgitation), the method may be useful in accurately determining maximum flow rates without interference from aliasing artifact.

The methods and methods described in this manual have been selected to reduce measurement errors and improve reproducibility of results. However, in some cases they may not be applicable for some clinical conditions, as well as for research protocols.

What equipment is required for Doppler sonography when assessing fetoplacental circulation?

• The equipment must have color and spectral Doppler modes, displaying on the monitor screen the speed scale of blood flow or pulse repetition frequency (PRF), as well as the Doppler frequency of the sensor used (in MHz).
• Mechanical Index (MI) and Temperature Index (TI) should be displayed on the monitor screen.
• The ultrasound system should display a blood flow velocity curve (BVR) based on the maximum flow velocity, displaying the full spectrum of the Doppler wave.
• It should be possible to clearly delineate the CSC using a system of automatic or manual delineation (tracing) of the curve shape.
• The system must have software that allows the estimation of peak systolic velocity (PSV), end-diastolic velocity (EDV) and time-averaged maximum speed of the KSK and calculate conventional Doppler indices such as pulsatility index (PI) and resistance index (RI) as well as systolic-diastolic ratio (S/D). The KSK trace must display points that reflect the values ​​that will be used for calculations to ensure the accuracy of the determined indices.

How can you optimize the accuracy of Doppler measurements?

Pulsed wave dopplerography

• Recording should be carried out during the absence of respiratory movements and motor activity of the fetus, and, if necessary, during the temporary holding of the mother’s breath.
• Color flow mapping is not mandatory, however it can be useful for identifying blood vessels of interest and determining the direction of blood flow.
• The optimal condition for insonation is complete coincidence of the direction of the ultrasound beam with the direction of blood flow. This provides ideal conditions for estimating absolute velocities and SSC spectra. Small deviations in the angle of insonation are acceptable.

  An insonation angle of 10 degrees corresponds to a 2% error in velocity measurement, while an angle of 20 degrees corresponds to a 6% error. When the absolute velocity measurement is a clinically important parameter (eg, in the middle cerebral artery, MCA) and the resulting angle is greater than 20 degrees, angle correction can be used, but this itself may cause error.

  If the measured parameters do not improve with repeated attempts to optimize insonation, a record should be made in the study protocol indicating the angle of insonation, as well as information about whether an angle correction was used or whether the velocities were recorded without its correction.

• It is recommended to begin the study with a relatively large Doppler gate (sample volume) setting on the pulsed wave Doppler to ensure that the maximum velocity spectrum is recorded throughout the cardiac cycle. If pulsation in nearby vessels interferes with the waveform being studied, the control volume can be reduced to improve recording quality. It must be remembered that the control volume can only be reduced in height (in the vertical direction), but not in width.
• Similar to the gray scale scanning mode, the scanning depth and resolution of the Doppler signal (beam) can be optimized by adjusting the frequency (MHz) of the transducer.
• A frequency filter (wall filter), also called a “low velocity reject,” “wall motion filter,” or “high pass filter,” is used to eliminating noise caused by the movement of the vessel walls.

  Traditionally it should be set to as low a value as possible (<50–60 Гц) для устранения низкочастотного шума от периферических кровеносных сосудов. При использовании высоких значений частотного фильтра, может создаваться ложный эффект отсутствия конечной диастолической скорости (EDV). (Рис. 4б).

• High frequency filter values ​​can be useful when assessing well-defined SSCs obtained from flows in structures such as the aortic and pulmonary outflow tracts. Setting the frequency filter to low values ​​in these cases may be accompanied by the appearance of noise in the form of “flow artifacts” near the baseline or after the valve closes.
• The horizontal sweep speed of the Doppler spectrum must be fast enough to allow successive systolic-diastolic cycles to be separately identified. The most optimal is the simultaneous display of 4 to 6 (but not more than 8–10) complete cardiac cycles. For fetal heart rates between 110 and 150 bpm, a sweep speed of 50 to 100 mm/s is adequate.
• The pulse repetition rate (PRF) should be adjusted depending on the vessel being examined: low PRF values ​​will allow visualization and accurate measurement of low-velocity blood flow; however, this will result in an aliasing artifact in the event of high-velocity regions. During Doppler measurements, the spectrum of the SSC should occupy at least 75% of the screen area (Fig. 3).
• Doppler measurements must be reproducible. If there are obvious discrepancies between measurement values, repeat measurements are recommended. Typically, the measurements closest to the expected ones are selected for the conclusion, with the exception of those obtained from spectra with low technical quality.
• In order to improve the quality of Doppler signal recording, it is necessary to carry out frequent real-time adjustments in gray scale mode or additionally use scanning in color Doppler mode. Then, when performing a CSC recording, after confirming in real time that the PW Doppler reference volume is positioned correctly, the two-dimensional (2D) and/or color Doppler (CD) modes should be frozen.
• You can confirm correct sample volume placement and optimize Doppler spectrum recording from a frozen 2D image by listening to the Doppler spectrum audio signal through audio speakers.
• The Doppler signal gain (Gain) must be adjusted so that the SSC spectrum can be clearly visualized, without artifacts in the background of the recording.
• It is recommended not to invert the flow direction on the monitor screen. When assessing the fetal heart and great vessels, it is very important to maintain the true direction of flow relative to the sensor when displayed in color in the Color Doppler mode and in the form of the direction of the FCS relative to the baseline in the Pulsed Wave Doppler mode. Traditionally, it is customary to map the blood flow directed to the ultrasound sensor in red, with the SSC spectrum located above the baseline, while the flow in the opposite direction (from the sensor) is displayed in blue and the SSC spectrum is located below the baseline.

Color Doppler mapping

• Compared to gray scale imaging, the use of color Doppler ultrasound increases the radiation power. The resolution of color Dopplerography increases with decreasing size of the “color window” (color box). It is necessary to pay close attention to the MI and TI indicators in view of the fact that their values ​​change depending on the size and depth of the “color window”.
• Increasing the size of the “color window” also leads to an increase in signal processing time and, as a consequence, a decrease in the frame rate. The “window” should be as small as possible and include only the area of ​​interest/area of ​​interest.
• The velocity scale or pulse repetition rate should be adjusted to reflect the actual color velocity of the vessel being examined. When high PRF values ​​are used, vessels with low blood flow velocities will not be displayed on the screen. When PRF values ​​are used too low, an aliasing artifact appears that appears as inappropriate color coding of velocities, giving the appearance of bidirectional flow.
• As with gray scale imaging, the resolution and scanning depth of color Doppler are dependent on the ultrasound frequency. To optimize signals, the color Doppler frequency must be adjusted accordingly.
• Gain should be adjusted to prevent noise and artifacts, which appear as random color signals appearing in the background of the screen.
• A frequency filter must be adjusted to remove noise coming from the area being examined.
• The angle of insonation significantly affects the color Doppler image; it must be adjusted by optimizing the position of the ultrasound transducer according to the position of the blood vessel or area of ​​interest. Energy and directional power Dopplerography
• All the same fundamental principles apply as for directional color Doppler.
• The angle of insonation has less influence on signal acquisition with power Doppler; however, when using this mode, the same image optimization techniques should be followed as for directional color Doppler.
• Aliasing artifact is not observed when using power Doppler PRF can lead to noise and artifacts.
• Gain should be reduced to prevent noise amplification (appears as a solid coloring of the background of the image).

Which technique should be used to evaluate Doppler waveforms of blood flow velocities in the uterine artery?

Using real-time color flow, the uterine artery is easily detected at the junction of the cervix and the body of the uterus. Measurement of Doppler blood flow velocities is usually performed in this position transabdominally (2, 3) or transvaginally (3–5). Taking into account that absolute values ​​of blood flow velocities do not have fundamental clinical significance, a semi-quantitative assessment of BSC is usually performed.

Measurements should be taken separately for the right and left uterine arteries, and the presence of dicrotic notching on the uterine artery should be noted.

Assessment of the uterine arteries in the first trimester. (Fig. 1)

Rice. 1. Curve of blood flow velocity in the uterine artery, obtained through transabdominal access in the first trimester of pregnancy.

1. Transabdominal method

• The midsagittal plane of the section of the uterus is displayed transabdominally and the course of the cervical canal is visualized. It is preferable for the mother's bladder to be empty.
• The sensor is shifted laterally until the choroid plexus in the paracervical region begins to be visualized.
• The color Doppler mode is turned on and the uterine artery is visualized in the area of ​​its turn in the cranial direction, where it begins to rise to the body of the uterus.
• Measurements are taken in the segment before the uterine artery begins to branch into the arcuate arteries.
• The same process is repeated on the opposite side.

2. Transvaginal method

• Transvaginally, the sensor is located in the anterior vaginal fornix. Next, a similar technique described for transabdominal access is used. The transducer is moved laterally until the paracervical choroid plexus is visualized, and the above steps are repeated in the same sequence as for the transabdominal method.
• Care must be taken to correctly differentiate the uterine arteries from the cervicovaginal (which have a cephalocaudal direction) or arcuate arteries. Velocities greater than 50 cm/s will be typical for the uterine arteries, which can be used to distinguish them from the arcuate arteries.

Evaluation of the uterine arteries in the second trimester (Fig. 2)

Rice. Fig. 2. Curves of blood flow velocities in the uterine artery obtained through transabdominal access in the second trimester of pregnancy. Normal (a) and pathological (b) spectrum; note the presence of a dicrotic notch (arrow) in the SSC spectrum (b).​

1.Transabdominal method

• Transabdominally, the sensor is located longitudinally in the lower lateral quadrant of the abdomen with an inclination in the medial direction. To detect the uterine artery, which is visualized at the intersection with the external iliac artery, color Doppler ultrasound is used.
• The control volume of pulsed wave Doppler is located along the blood flow of the uterine artery 1 cm below the point of intersection of the two vessels. In those rare cases where the uterine artery bifurcates before its intersection with the external iliac artery, the control volume should be set to the segment up to its bifurcation.
• The same process is repeated for the uterine artery on the opposite side.
• As pregnancy progresses, the uterus usually rotates to the right. Therefore, the left uterine artery will not be defined as laterally as the right one.

2. Transvaginal method

• The woman must empty her bladder and is in the dorsal lithotomy position. The sensor should be located in the lateral vaginal vault, the uterine artery is determined using color Doppler ultrasound at the level of the internal os lateral to the cervix.
• The same process is repeated for the uterine artery on the opposite side. It must be remembered that the standard values ​​of Doppler indices in the uterine arteries depend on the measurement method, therefore, for transabdominal (3) and transvaginal (5) access, appropriate standards must be used. In this case, the scanning technique should be similar to that which was used to obtain these standard values.

Note. In women with congenital uterine anomalies, assessment of uterine artery Doppler indices and their interpretation are not reliable since all studies were performed on women with (assumed) normal anatomy.

What technique should be used to evaluate Doppler waveforms of blood flow velocities in the umbilical artery?

There is a significant difference in Doppler measurements measured at the fetal end, the free loop, and the placental end of the umbilical cord (6). The highest resistance is seen at the fetal end, and thus null/reversed end-diastolic flow is most likely to be detected at this site first. Normative values ​​of Doppler indices assessed at this location of the umbilical cord artery have been published in the literature (7, 8).

For the sake of simplicity and consistency, measurements should be taken at the level of the free loop of the umbilical cord. However, in cases of multiple pregnancies, and/or for comparison of repeated measurements over time, recording blood flows at “fixed sites”, for example, in the region of the fetal end, placental end or intra-abdominal segment, may be more reliable.

Rice. 3. Acceptable (a) and unacceptable (b) registration of blood flow velocity curves in the umbilical cord artery. In image (b), the blood flow spectrum is very shallow and the horizontal scan speed is too slow.

Rice. 4. Spectrum of umbilical cord artery flow velocity curves obtained from the same fetus at 4 min intervals showing (a) normal flow and (b) apparent very low diastolic flow and absence of flow signals near the baseline resulting from use inadequate setting of the frequency filter (which is set too high).

Depending on where the blood flow assessment was performed, appropriate guideline values ​​must be used. In Fig. Figure 3 shows acceptable and unacceptable recording of blood flow velocity curves. Rice. 4 demonstrates the influence of the frequency filter on the appearance of the CSC.

Note. 1) In cases of multiple pregnancies, assessing blood flow in the umbilical cord artery can be difficult, due to the difficulty of determining which fetus belongs to a particular umbilical cord loop. In these cases, it is best to assess blood flow just distal to the umbilical cord's insertion into the fetal anterior abdominal wall.

However, vascular resistance in this area will be higher than at the level of the free loop or placental end, therefore it is necessary to use the appropriate standard values. 2) In the case of the presence of only two vessels in the umbilical cord, at any stage of pregnancy, the diameter of the single umbilical cord artery will be larger than in the presence of 2 arteries, and accordingly, vascular resistance will be lower (9).

What technique should be used to evaluate Doppler waveforms of blood flow velocities in the middle cerebral artery?

• A cross-section of the fetal head at the level of the thalamus and wings of the pterygoid should be drawn and the image magnified.
• To visualize the circle of Willis and the proximal part of the middle cerebral artery, the Color Doppler mode should be used (Fig. 5).
• The PW Doppler reference volume should be placed at the proximal third of the MCA in close proximity to its origin from the internal carotid artery (10) because systolic velocity decreases with increasing distance from the origin of this vessel.
• The angle between the ultrasound beam and the direction of blood flow should be kept as close to 0° as possible (Fig. 6).
• It is necessary to ensure that there is no excessive pressure on the fetal head.
• Simultaneous registration of at least 3, but not more than 10 consecutive cardiac cycles of CSC should be carried out. The highest point of the curve corresponds to the peak systolic velocity PSV (cm/s).
• PSV measurement can be done manually using callipers or using automatic tracing. The latter gives significantly lower average values ​​compared to the first method (using callipers), but is closest to the published average values ​​used in clinical practice (11). PI is usually calculated using automatic tracing, but manual delineation is also acceptable.
• Appropriate standards should be used to interpret the results. The measurement technique should be similar to that used to obtain standard values.

Rice. 5. Color Doppler mapping of the Circle of Willis.

Rice. 6. Acceptable recording of blood flow velocity curves in the middle cerebral artery. Notice the insonation angle is close to 0°.

What technique should be used to evaluate Doppler waveforms of fetal venous blood flow velocities?

Ductus venosus (Fig. 7 and 8)

• The ductus venosus (DV) connects the intra-abdominal segment of the umbilical vein with the superior portion of the inferior vena cava just below the diaphragm. This vessel can be visualized in gray scale (2D) mode in a midsagittal section of the fetal body or in an oblique cross section of the upper abdomen (12).
• At the narrow ostium of the ductus venosus, the circulatory system exhibits high-velocity flow, which helps to identify this vessel and determines the standard location for the control volume when performing Doppler measurements (13).
• Doppler measurements can best be obtained by scanning in a sagittal section from the anterioinferior aspect of the fetal abdomen, since the position of the reference volume in the isthmus can then be easily monitored. The sagittal approach through the chest can also be used, but requires greater skill from the operator. The oblique section provides acceptable access from an anterior or posterior position, allowing for adequate CVS appearance, but with less control over the angle of insonation and absolute velocities.
• In the early stages of pregnancy and in cases of pregnancy pathology, special attention should be paid to choosing an adequately small control volume of pulsed wave Doppler in order to achieve clear registration of low-velocity flows in the atrial systole phase.
• The spectrum of blood flow velocity curves usually has a three-phase appearance, but in rare observations, a biphasic or monophasic spectrum can also be recorded in healthy fetuses (14).
• During the second and third trimesters of pregnancy, relatively high blood flow velocities of 55 to 90 cm/s are recorded (15), but in early pregnancy these values ​​are usually lower.

Rice. 7. Registration of the Doppler spectrum in the venous duct from the sagittal approach with the location of the control volume in the isthmus region without adjusting the angle. The low-pass filter (arrow) does not interfere with the registration of the a-wave (a), which is recorded significantly above the zero line. High horizontal scan speed allows detailed visualization of velocity changes during the cardiac cycle.

Rice. 8. Blood flow spectrum recorded in the ductus venosus, which shows increased pulsatility at 36 weeks (a). Interference, which is highly echogenic noise along the baseline, makes it difficult to confirm the presence of a reversal component during atrial systole (indicated by triangles). (b) repeated recording with slightly increased frequency filter values ​​(arrow) improves the quality of the waveform recording and the clarity of visualization of reverse blood flow in the systole phase

What indicators to use?

Systole-diastolic ratio, RI and PI are three generally accepted indicators for describing arterial blood flow velocity curves. All three indicators are closely interrelated. PI shows a linear relationship with vascular resistance, in contrast to S/D and RI, which are characterized by a parabolic relationship with increasing vascular resistance (16).

In addition, PI does not lose its meaning in the case of zero or negative values ​​of diastolic blood flow. PI is the most commonly used index in modern clinical practice.

By analogy, according to current literature, the pulsatility index for veins (PIV) is the most widely used indicator for assessing venous blood flow velocity curves (17). In some situations, the use of absolute rates may be preferable to semi-quantitative index measures.

Literature

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2. Aquilina J, Barnett A, Thompson O, Harrington K. Comprehensive analysis of uterine artery flow velocity waveforms for the prediction of pre-eclampsia. Ultrasound Obstet Gynecol 2000; 16: 163–170.

3. Gomez O, Figueras F, Fern(andez S, Bennasar M, Martinez JM, Puerto B, Gratacos E. Reference ranges for uterine artery mean pulsatility index at 11–41 weeks of gestation. Ultrasound Obstet Gynecol 2008; 32: 128– 132.

4. Jurkovic D, Jauniaux E, Kurjak A, Hustin J, Campbell S, Nicolaides KH. Transvaginal color Doppler assessment of the uteroplacental circulation in early pregnancy. Obstet Gynecol 1991; 77:365–369.

5. Papageorghiou AT, Yu CK, Bindra R, Pandis G, Nicolaides KH; Fetal Medicine Foundation Second Trimester Screening Group. Multicenter screening for pre-eclampsia and fetal growth restriction by transvaginal uterine artery Doppler at 23 weeks of gestation. Ultrasound Obstet Gynecol 2001; 18:441–449.

6. Khare M, Paul S, Konje J. Variation in Doppler indices along the length of the cord from the intraabdominal to the placental insertion. Acta Obstet Gynecol Scand 2006; 85:922–928.

7. Acharya G, Wilsgaard T, Berntsen G, Maltau J, Kiserud T. Reference ranges for serial measurements of blood velocity and pulsatility index at the intra-abdominal portion, and fetal and placental ends of the umbilical artery. Ultrasound Obstet Gynecol 2005; 26: 162–169.

8. Acharya G, Wilsgaard T, Berntsen G, Maltau J, Kiserud T. Reference ranges for serial measurements of umbilical artery Doppler indices in the second half of pregnancy. Am J Obstet Gynecol 2005; 192:937–944.

9. Sepulveda W, Peek MJ, Hassan J, Hollingsworth J. Umbilical vein to artery ratio in fetuses with single umbilical artery. Ultrasound Obstet Gynecol 1996; 8:23–26.

10. Mari G for the collaborative group for Doppler assessment. Noninvasive diagnosis by Doppler ultrasonography of fetal anemia due to maternal red-cell alloimmunization. N Engl J Med 2000; 342:9–14.

11. Patterson TM, Alexander A, Szychowski JM, Owen J. Middle cerebral artery median peak systolic velocity validation: effect of measurement technique. Am J Perinatol 2010; 27: 625–630.

12. Kiserud T, Eik-Nes SH, Blaas HG, Hellevik LR. Ultrasonographic velocimetry of the fetal ductus venosus. Lancet 1991; 338:1412–1414.

13. Acharya G, Kiserud T. Pulsations of the ductus venosus blood velocity and diameter are more pronounced at the outlet than at the inlet. Eur J Obstet Gynecol Reprod Biol 1999; 84: 149–154.

14. Kiserud T. Hemodynamics of the ductus venosus. Eur J Obstet Gynecol Reprod Biol 1999; 84: 139–147.

15. Kessler J, Rasmussen S, Hanson M, Kiserud T. Longitudinal reference ranges for ductus venosus flow velocities and waveform indices. Ultrasound Obstet Gynecol 2006; 28:890–898.

16. Ochi H, Suginami H, Matsubara K, Taniguchi H, Yano J, Matsuura S. Micro-bead embolization of uterine spiral arteries and uterine arterial flow velocity waveforms in the pregnant woman. Ultrasound Obstet Gynecol 1995; 6:272–276.

17. Hecher K, Campbell S, Snijders R, Nicolaides K. Reference ranges for fetal venous and atrioventricular blood flow parameters. Ultrasound Obstet Gynecol 1994; 4: 381–390.