Introduction to Doppler - USA

Welcome to the Introduction to Doppler on-line course. Doppler is a diverse tool, with a broad scope that translates across all ultrasound modalities.   Throughout this course we will use Doppler examples from a variety of ultrasound modalities so that you can be introduced to common Doppler tools and Doppler modes.   The most common use of Doppler is to measure or monitor dynamic changes in blood flow or hemodynamics and the complexity of hemodynamics can require multiple Doppler modes.   For example, on this page there are two Doppler modes being utilized to assess the venous flow pattern and the direction of the blood flow.   Doppler methods are specific to each ultrasound modality, laboratory, and methods can fluctuate between regions.   A complete discussion employing specific modality techniques and protocols is beyond the scope of this course.     So, let’s get started.   Congratulations. You have just finished the Introduction To Doppler course. Take time now to review the material here and in the glossary that follows before proceeding to the final assessment. Link to the course review Listed below are the key points that have been presented. Relate variables and limitations associated with the Doppler equation, frequency shift, and velocity estimation. Describe pulsed, spectral, and continuous wave Doppler modalities. Pulse Doppler instrumentation estimates the velocity and direction of blood flow within a vessel, chamber, or heart valve by pulse sampling within the range gate or averaged across a series of range gates.   Pulsed wave (PW) spectral Doppler and Color Doppler are pulse Doppler modes. The pulse repetition frequency (PRF) controls the range of velocities displayed.      See the exercises below for more information on pulsed Doppler modes and display. Pulsed Doppler Learn more about pulsed Doppler modes. Slide NumberText BlocksCalloutsAudio ScriptImage File1PW Range Gate Range resolution is the velocity and direction of blood flow that is specific to a location and the location is the PW Doppler range gate.    The range gate is a box integrated with the PW Doppler cursor line. The range gate is positioned to interrogate at a specific location and depth along the cursor. Doppler instrumentation pulses out from the range gate or gates, and echoes return indicating the frequency shift. Angle correction is applied to the range gate to solve for the velocity at the location of the range gate.  The gate size can be adjusted to sample a larger or smaller range. PW Range Gate Range resolution is the velocity and direction of blood flow that is specific to a location and the location is the PW Doppler range gate. The range gate is a box integrated with the PW Doppler cursor line. The range gate is positioned to interrogate at a specific location and depth along with the cursor. Angle correction is applied to the range gate to solve for the velocity at the location of the range gate. The gate size can be adjusted to sample a larger or smaller range. 2Frequency Shift At a given depth, a single range gate will send pulses at a given frequency, the direction of blood flow is based on the arrival time of the reflector back to the range gate.  The frequency shift of blood cells moving toward the range gate produces positive frequency shift and a negative frequency shift indicates blood cells are moving away. The frequency shift from blood cells is converted to a spectrum display (covered later in the course).  The frequency shift from blood flow is weak and usually within the audible range. Typically, the audio speakers on the ultrasound system will assign the right speaker to positive frequency shift and the left speaker to the negative frequency shift.  Listening to PW Doppler from blood flow, you can detect increasing and decreasing intensity of the resulting sound.  Frequency Shift At a given depth, a single range gate sends pulses at a given frequency, the direction of blood flow based on the arrival time of the reflector returning to the range gate. The frequency shift of blood cells moving toward the range gate produces positive frequency shift and a negative frequency shift indicates blood cells are moving away. The frequency shift from blood cells is converted to a spectrum display (covered later in this course). The frequency shift from blood flow is weak and usually within the audible range. Typically, the audio speakers on the ultrasound system will assign the right speaker to positive frequency shift and the left speaker to the negative frequency shift. Listening to PW Doppler from blood flow, you can detect increasing and decreasing intensity of the resulting sound. 3Baseline Shift Manually adjusting the baseline down will optimize flow above the baseline. Moving the baseline up maximizes flow below the baseline.  In this PW Doppler, the spectral signal is being ‘cut-off’ because the velocity range is too small above the baseline. Moving the baseline yields more velocity range for the spectral tracings to display and removes the ‘cut-off’ of the spectral signal. Increasing the scale or moving the baseline will display the complete spectral signal.Moving the baseline yields more velocity range for the spectral tracings to display and removes the ‘cut-off’ of the spectral signal.In this PW Doppler, the spectral signal is being ‘cut-off’ because the velocity range is too small above the baselineBaseline Shift Manually adjusting the baseline down will optimize flow above the baseline. Moving the baseline up maximizes flow below the baseline. In this PW Doppler, the spectral signal is being ‘cut-off’ because the velocity range is too small above the baseline. Moving the baseline yields more velocity range for the spectral tracings to display and removes the ‘cut-off’ of the spectral signal. Increasing the scale or moving the baseline will display the complete spectral signal. 4Color Doppler Packets Color Doppler detects the average frequency shift and direction from a series of small range gates or color packets spaced throughout the color Doppler region of interest (ROI). The size and density of color packets can be increased or decreased within the color ROI.   The frequency shift is determined across the ROI at each gate/packet. At each packet, the corresponding frequency shift detected is compared to the previous frequency shift result. This comparison determines movement, direction, and the mean frequency shift.   Doppler instrumentation does not apply an angle to each packet within the ROI, so color Doppler solves for the mean frequency shift.    Color Doppler instrumentation codes the direction of flow as either moving toward or away from the color ROI.  Commonly, color flow Doppler is red in one direction and blue in the other direction.Color Doppler Packets Color Doppler detects the average frequency shift and direction from a series of small range gates or color packets spaced throughout the color Doppler region of interest or ROI. The size and density of color packets can be increased or decreased within the color region of interest. The frequency shift is determined across the region of interest at each gate or packet. At each packet, the corresponding frequency shift detected is compared to the previous frequency shift result. This comparison determines movement, direction, and the mean frequency shift. Doppler instrumentation does not apply an angle to each packet within the region of interest, so color Doppler solves for the mean frequency shift. Doppler instrumentation codes the direction of flow as either moving toward or away from the color region of interest. Commonly, color flow Doppler is red in one direction and blue in the other direction. Scale, PRF, Nyquist Learn more about pulsed Doppler displays. Slide NumberText BlocksCalloutsAudio ScriptImage File1PRF and Scale Pulse Repetition Frequency or PRF is the frequency that pulses occur over one second.  PRF is the amount of time pulsing and spent listening. Adjusting the PRF controls the scale which is the range of velocities that can be displayed in both the positive and negative direction.  In Image A - PW spectral example note the velocity range above the baseline is 100 cm/s and below the baseline the maximum velocity is -50 cm/s. On Image B - this “color bar” is the maximum velocity range that can be displayed note the maximum velocity that can be displayed is 63 cm/s in either direction.Image A Image B PRF and Scale Pulse Repetition Frequency or PRF is the frequency that pulses occur over one second. PRF is the amount of time pulsing and spent listening. Adjusting the PRF controls the scale which is the range of velocities that can be displayed in both the positive and negative direction. In Image A – This is a pulse wave spectral example, note the velocity range above the baseline is 100 cm/s and below the baseline the maximum velocity is -50 cm/s. On Image B - This “color bar” is the maximum velocity range that can be displayed note the maximum velocity that can be displayed is 63 cm/s in either direction. 2Nyquist Limit In pulsed Doppler instrumentation, the Nyquist limit is the highest velocity that can be displayed in either direction.   The Nyquist limit is twice the pulse repetition frequency (PRF). So, the PRF must be twice as high as the highest frequency shift (Doppler shift) to be displayed.   If the maximum velocity was 61 cm/s, the velocity range exceeds the Nyquist limit on color bar A. However, on color bars B and C, a velocity of 61 cm/s does not exceed the Nyquist limit and would display without aliasing.  A            B             C Nyquist limit In pulsed Doppler instrumentation, the Nyquist limit is the highest velocity that can be displayed in either direction. The Nyquist limit is twice the pulse repetition frequency (PRF). So, the PRF must be twice as high as the highest frequency shift (Doppler shift) to be displayed. If the maximum velocity was 61 cm/s, the velocity range exceeds the Nyquist limit on color bar A. However, on color bars B and C, a velocity of 61 cm/s does not exceed the Nyquist limit and would display without aliasing. 3Aliasing The Nyquist limit limits the maximum velocity attainable in pulse wave and color Doppler. When the velocity scale cannot display the entire velocity range aliasing will occur. Aliasing is a false signal. These images are the same, only the scale or PRF has changed. Image A aliasing occurs at 24 cm/s. Image B, expanding the scale to 29 cm/s reduces the aliasing. Image C, the color scale is optimized at 75 cm/s. Image A                                 Image B                                    Image C Aliasing The Nyquist limit limits the maximum velocity attainable in pulse wave and color Doppler. When the velocity scale cannot display the entire velocity range aliasing will occur. Aliasing is a false signal. These images are the same, only the scale or PRF has changed. Image A aliasing occurs at 24cm/s. Image B, expanding the scale to 29 cm/s reduces the aliasing. Image C, the color scale is optimized at 75 cm/s. 4Color Doppler Aliasing In this progression of images, the color Doppler ROI is over the common femoral vein. The patient is performing a Valsalva maneuver to assess for venous valve incompetence or venous reflux. The patient exhales and at this point there is no signal.The venous flow is moving normally toward the head, away from the color ROI.Venous reflux, rapidly moving backwards past the incompetent vein creates a high-velocity signal beyond the velocity range of the color scale.The patient breaths inward and begins to Valsalva. The flow moves abnormally, toward the feet, toward the color ROI.The patient releases the Valsalva, venous flow begins to move normally toward the head, and there is some to-and-fro movement.In this example, it is technically ideal to keep the color scale low enough to optimize the venous color flow Doppler during normal respiration.   The aliasing in color flow Doppler demonstrates the hemodynamic information alongside the normal venous flow that precedes the aliasing.Aliasing Example on Color Doppler In this progression of images, the color Doppler ROI is over the common femoral vein. The patient is performing a Valsalva maneuver to assess for venous valve incompetence or venous reflux. Frame 1. The venous flow is moving normally toward the head, away from the color ROI. Frame 2. The patient breaths inward and begins to Valsalva. The flow moves abnormally, toward the feet, toward the color ROI. Frame 3. Venous reflux, rapidly moving backwards past the incompetent vein creates a high-velocity signal beyond the velocity range of the color scale. Frame 4. The patient releases the Valsalva, venous flow begins to move normally toward the head, and there is some to-and-fro movement. Frame 5. The patient exhales and at this point there is no signal. In this example, it is technically ideal to keep the color scale low enough to optimize the venous color flow Doppler during normal respiration. The aliasing in color flow Doppler demonstrates the hemodynamic information alongside the normal venous flow that precedes the aliasing. 5Aliasing Example PW Doppler This is a PW Doppler evaluation over the same area as the previous page.   The PW Doppler is sampling in the common femoral vein just below the incompetent valve. The patient repeats the Valsalva maneuver and the spectral signal aliases at the point of venous reflux.   The aliasing in PW Doppler demonstrates the hemodynamic information alongside the normal venous flow that precedes the aliasing.CalloutsVenous reflux causing aliasing of the spectral signal.Normal venous flow.Aliasing Example on pulse wave Doppler This is a PW Doppler evaluation over the same area as the previous page. The PW Doppler is sampling in the common femoral vein just below the incompetent valve. The patient repeats the Valsalva maneuver and the spectral signal aliases at the point of venous reflux. The aliasing in PW Doppler demonstrates the hemodynamic information alongside the normal venous flow that precedes the aliasing. Documenting the spectrum of velocities, direction, and patterns are made using spectral Doppler.       Explore spectral Doppler below. Spectral Doppler Explore spectral Doppler. Instructions:Flash File:HTML5 File:/content/generator/Course_90022407/SpectralDoppler_V5_800x600/index.htmlPDF File: PW Doppler or PW, are common names for Pulse Wave Doppler.   Explore the exercise below on Pulse Wave Doppler.   Pulse Wave Doppler Mode Learn more about pulse wave Doppler. Instructions:Flash File:HTML5 File:/content/generator/Course_90022407/PWDoppler_V6_800x600/index.htmlPDF File: Continuous wave Doppler is commonly known as CW Doppler or CW. CW Doppler is a spectral Doppler modality. Learn more about CW Doppler below. * This image is utilizing a vector transducer to assess regurgitation from an aortic valve. Two Doppler modes are being utilized: color Doppler and CW Doppler to assess the aortic valve.    CW Doppler Learn More about CW Doppler. Slide NumberText BlocksCalloutsAudio ScriptImage File1CW Doppler collects the spectrum of signals along the entire Doppler line. In PW, Doppler instrumentation is sending and then listening for the frequency shift. In CW, Doppler instrumentation uses two independent piezoelectric elements that are continuously sending and receiving along the line of transmission.Continuous wave or CW Doppler collects the spectrum of signals along the entire Doppler line. In PW, Doppler instrumentation is sending and then listening for the frequency shift. In CW, Doppler instrumentation uses two independent piezoelectric elements that are continuously sending and receiving along the line of transmission. 2The Nyquist limit does not limit CW Doppler. Therefore, CW Doppler can detect unusually high velocities. However, while sampling with CW anything that is moving within the transmission line will contribute to the frequency shift. CW Doppler is also angle dependent. This is a CW Doppler of a mitral valve regurgitation gradient. The CW Doppler velocity range is set at a maximum velocity of 8 m/s or meters per second.  CalloutsMaximum velocity above the baseline.Maximum velocity below the baseline.The Nyquist limit does not limit CW Doppler. Therefore, CW Doppler can detect unusually high velocities. However, while sampling with CW anything that is moving within the transmission line will contribute to the frequency shift. CW Doppler is also angle dependent. This is a CW Doppler of a mitral valve regurgitation gradient. The CW Doppler velocity range is set at a maximum velocity of 8 m/s or meters per second. 3CW Doppler has a wide range of applications and is a routine tool used in cardiac imaging. CW Doppler is typically available on phased or vector transducers.CW Doppler has a wide range of applications and is a routine tool used in cardiac imaging. CW Doppler is typically available on phased or vector transducers. 4Both examples here show CW Doppler in tricuspid valve regurgitation.    This frame has increased the time ‘sweep speed’ to stretch out the signal and display the spectrum of frequencies collected at the regurgitate tricuspid valve.Both examples here show CW Doppler in tricuspid valve regurgitation. This frame has increased the time ‘sweep speed’ to stretch out the signal and display the spectrum of frequencies collected at the regurgitate tricuspid valve. 5Blind or Dedicated CW Doppler As the name implies, there is not a 2D image to guide Doppler cursor placement. The Doppler crystals are dedicated only to the continuous Doppler signal. The small footprint allows for extreme angulation of the Doppler probe.   Application of dedicated CW Doppler is an integral part of a sophisticated echocardiography department. Using the non-imaging transducer is part of a cardiac Doppler examination for the most accurate Doppler shift of valvular velocities through stenotic and regurgitant lesions.   In peripheral vascular ultrasound, the blind continuous wave Doppler is used on the skin surface to angle very acutely on the skin and into the blood flow to assess the pulsatility of the arteries in the upper and lower extremities.Blind or Dedicated CW Doppler As the name implies, there is not a 2D image to guide Doppler cursor placement. The Doppler crystals are dedicated only to the continuous Doppler signal. The small footprint allows for extreme angulation of the Doppler probe. Application of dedicated CW Doppler is an integral part of a sophisticated echocardiography department. Using the non-imaging transducer is part of a cardiac Doppler examination for the most accurate Doppler shift of valvular velocities through stenotic and regurgitant lesions.   Explore other Doppler uses in this exercise.   Footnote: The image on this page is a short axis view of the aortic valve where the ostium of two coronary arteries are identified using color Doppler. Other Doppler Explore other Doppler examples here. Slide NumberText BlocksCalloutsAudio ScriptImage File1A - Example color Doppler used with M-mode (motion mode) to reveal the inflow pattern of the left ventricle thru the mitral valve.B - Image with color Doppler mitral regurgitation is shown below the closed mitral valve.C - An example of volumetric1 color Doppler showing mitral valve regurgitation. 1. eSie PISA™ volume analysis package utilizing real-time 4D volume  imaging.       A is an example color Doppler used with M-Mode (motion mode) to reveal the inflow pattern of the left ventricle thru the mitral valve. B is an image with color Doppler showing mitral regurgitation below the closed mitral valve. C is an example of volumetric color Doppler showing mitral valve regurgitation. 2Color Doppler is useful to map locations that would be difficult to identify otherwise.A - shows how color Doppler to used to help identify a small branch vessel the external carotid artery.B - Identifying middle cerebral artery within the circle of Willis. C - In this short axis view of the aortic valve, the ostium of two coronary arteries are identified.Color Doppler is useful to map locations that would be difficult to identify otherwise. Image A shows how color Doppler is used to help identify a small branch vessel, the external carotid artery. On image B color Doppler is used to identify the middle cerebral artery within the circle of Willis. C is a short axis view of the aortic valve where the ostium of two coronary arteries are identified using color Doppler. 3This is color Doppler showing regurgitation through an aortic valve imaging at a high frequency, very close to the valve from the esophagus (trans-esophageal).This is color Doppler showing regurgitation through an aortic valve imaging at a high frequency, very close to the valve from the esophagus using a trans-esophageal transducer.4Using color Doppler over areas of subclinical renal calculi demonstrate a reverberation signal. Using color Doppler over areas of subclinical renal calculi demonstrate a reverberation signal.5Color Doppler shows urine flow moving into the bladder and helps to demonstrate patency from the left ureter.Color Doppler shows urine flow moving into the bladder and helps to demonstrate patency from the left ureter. The Doppler effect is named for Christian Doppler (1803-1853) for his principle, “The Doppler Effect” in 1842.  Doppler described that the frequency of a light and sound wave depends on the relative speed of the source and the observer. Doppler effect is the perceived change in frequency of sound or light, by the observer. The change in frequency indicates movement.   Doppler is used in diagnostic medical ultrasound to detect and evaluate hemodynamics. The blood movement, velocity, and direction in real-time.   Please review the exercises below for more information. Doppler Introduction Learn more about Doppler effect. Instructions:StartFlash File:HTML5 File:/content/generator/Course_90022407/Doppler_V4_800x600/index.htmlPDF File: The Doppler instrumentation within the ultrasound equipment uses the Doppler equation to solve for velocity and direction of blood cells.  Please review the information below for more information on solving for direction and velocity.  Velocity Direction Learn more about solving for velocity and direction. Slide NumberText BlocksCalloutsAudio ScriptImage File1Solving for Direction Doppler shift is frequency shift and this shift in frequency is relative to the observer. In diagnostic medical ultrasound, the observer is the transducer. The frequency shift is the difference between the transmitted frequency (from the transducer) and the reflected frequency from *blood cells. The frequency shift decreases when blood cells are moving away from the transducer. Frequency shift increases when blood cells are moving toward the transducer.*Unless otherwise noted, the remaining sections of this course will assume that the source is from the blood cells within blood vessels.Solving for Direction Doppler shift is frequency shift and this shift in frequency is relative to the observer. In diagnostic medical ultrasound, the observer is the transducer. The frequency shift is the difference between the transmitted frequency (from the transducer) and the reflected frequency from *blood cells. The frequency shift decreases when blood cells are moving away from the transducer. Frequency shift increases when blood cells are moving toward the transducer. 2Solving for Velocity The Doppler equation assumes that the observer is in line with the received signal. If the transducer is directly in line with the blood cells, the angle of intercept is zero. The cosign of a zero is one.   In clinical practice, a zero angle is difficult. Using angle correction, the operator adjusts the angle of intercept, so the Doppler aligns to the anatomy.      Solving for Velocity The Doppler equation assumes that the observer is in line with the received signal. If the transducer is directly in line with the blood cells, the angle of intercept is zero. The cosign of a zero is one. In clinical practice, an angle of zero is difficult. Using angle correction, the operator adjusts the angle of intercept, so the Doppler aligns to the anatomy.3Angle Correction The Doppler instrumentation solves for the velocity of the blood cells using the cosign of the angle.   Every change in the angle of intercept away from zero changes the velocity of the returned signal.   The cosign of zero is one, and cosign of 90 is zero. The frequency shift will increase as the angle approaches zero.   The frequency shift will get smaller as the angle approaches 90 degrees.   When blood flow is 90 degrees to the transducer, the Doppler equation is multiplied by the cosign of 90 degrees, which is zero.   Therefore, at 90 degrees, there is no signal perceived.     0 1     1 Angle Correction The Doppler instrumentation solves for the velocity of the blood cells using the cosign of the angle. Every change in the angle of intercept away from zero changes the velocity of the returned signal. The cosign of zero is one, and cosign of 90 is zero. The frequency shift will increase as the angle approaches zero. The frequency shift will get smaller as the angle approaches 90 degrees. When blood flow is 90 degrees to the transducer, the Doppler equation is multiplied by the cosign of 90 degrees, which is zero. Therefore, at 90 degrees, there is no signal perceived. Color Doppler is a pulse sampling technique.   Learn more below.     Color Doppler Mode Learn more about color Doppler imaging. Instructions:First Color Doppler PopupFlash File:HTML5 File:/content/generator/Course_90022407/Popup1_ColorDopplerMode_V2_800x600/index.htmlPDF File: Color Doppler Mode Learn more about color Doppler (continued). Instructions:Second Color Doppler PopupFlash File:HTML5 File:/content/generator/Course_90022407/Popup2_COlorDoppler_V2_800x600/index.htmlPDF File: The reproduction, transmission or distribution of this training or its contents is not permitted without express written authority. Offenders will be liable for damages.   All names and data of patients, parameters and configuration dependent designations are fictional and examples only. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.   ACUSON Sequoia is a trademark of Siemens Medical Solutions USA, Inc.   Copyright © Siemens Healthcare GmbH, 2020.  Please note that the learning material is for training purposes only! For the proper use of the software or hardware, please always use the Operator Manual or Instructions for Use (hereinafter collectively “Operator Manual”) issued by Siemens Healthineers. This material is to be used as training material only and shall by no means substitute the Operator Manual. Any material used in this training will not be updated on a regular basis and does not necessarily reflect the latest version of the software and hardware available at the time of the training.   The Operator Manual shall be used as your main reference, in particular for relevant safety information like warnings and cautions. Note: Some functions shown in this material are optional and might not be part of your system. The information in this material contains general technical descriptions of specifications and options as well as standard and optional features that do not always have to be present in individual cases.   Certain products, product-related claims or functionalities described in the material (hereinafter collectively “Functionality”) may not (yet) be commercially available in your country. Due to regulatory requirements, the future availability of said Functionalities in any specific country is not guaranteed. Please contact your local Siemens Healthineers sales representative for the most current information. Upon successful completion of this course, you will be able to: Relate variables and limitations associated with the Doppler equation, frequency shift, and velocity estimation. Describe pulsed, spectral, and continuous wave Doppler modalities. It is not essential to memorize the equation but to understand how the components of the equation relate to one another.   Please review each of the components of the Doppler equation below. Doppler Equation Learn more about the Doppler equation. Slide NumberText BlocksCalloutsAudio ScriptImage File1Δf = [2 * v * cos(θ) * f0 ] / c  The change in frequency is equal to the velocity difference multiplied by the cosign of the angle of intercept that is multiplied by the transmitted frequency and this product is divided by the speed of sound.The change in frequency is equal to the velocity difference multiplied by the cosign of the angle of intercept that is multiplied by the transmitted frequency and this product is divided by the speed of sound. Glossary and references avaliable here. Glossary Glossary Select the glossary link below: Glossary Link References References Selec tthe references link below: Reference Link