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Contrast-Enhanced Echocardiography - ACUSON Redwood™ Ultrasound System USA

This course will familiarize the learner with the basics of contrast-enhanced echocardiography,  left ventricular opacification (LVO) and a familiarization of LVO on the ACUSON Redwood™ Ultrasound System.  

Upon completion of this course, the learner will be able to: Understand the physical properties and behaviors of the microbubble within the acoustic field Relate some of the ACUSON Redwood ultrasound systems instrumentation that influences the microbubble Congratulations, you have just finished the online course Contrast-Enhanced Echocardiography for ACUSON Redwood™.  Listed below are the key points. Take time now to review the material here before proceeding to the final assessment. Course Review Understand the physical properties and behaviors of the microbubble within the acoustic field. Relate some of the ACUSON Redwood Ultrasound Systems instrumentation that influences the microbubble. Welcome to the ACUSON Redwood™ ultrasound system Contrast-Enhanced Echocardiography for Left Ventricular Opacification (LVO).  The ACUSON Redwood ultrasound system has an intuitive touch screen layout that is streamlined to include only the functions necessary to confidently perform LVO exams. When clinically indicated, contrast-enhanced echocardiograms for Left Ventricular Opacification (LVO) can facilitate wall motion assessment and provide diagnostic confidence. Additionally, in this course you will be introduced to a high-level general overview of the physical properties of the microbubble used in contrast-enhancement for LVO. 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 Redwood 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. Contrast-enhanced echocardiography improves the endocardial border detection. Currently, the only United States, Food and Drug Administration (U.S. FDA) approved use of Contrast-enhanced echocardiography is for Left Ventricular Opacification often referred to as LVO.  In this example, the contrast-enhancing agent is enhancing the detection of the endocardial border to facilitate wall motion assessment. Contrast enhancement is appropriate when two or more adjacent segments of the left ventricle are suboptimal, limiting the evaluation of the structure and function. Contrast-Enhancement Learn more contrast-enhancement for echocardiography. Tab TitleTextBrief history of LVO Contrast-enhancing agents are microbubbles that generate harmonic energy within the acoustic field, providing a stable grey-scale enhancement. However, first generation contrast enhancing agents (CEA) were developed for echocardiography in the era before harmonic imaging. The U.S. FDA approved the first generation CEA in 1994 that was an air-based CEA. This first generation CEA did improve Doppler spectral profiles and provided some grey-scale enhancing effect, but proved to be highly diffusible lasting about 30 seconds in the left ventricle. In Europe, the two first generation CEA released in 1991 and 1996. Similarly, these CEAs did improve the ultrasound intensity of the blood pool but had small amplitude responses in the acoustic field. Second-generation agents were designed for stability while oscillating within the acoustic field.   Harmonic imaging caused the second-generation agents to oscillate and generate harmonic energy within the acoustic field. Appropriateness of LVO LVO contrast-enhancement is appropriate to use in echocardiography for technically difficult-to-image patients. When two or more adjacent segments of the left ventricle are suboptimal, this can limit the evaluation of the cardiac structure and function for resting and stress echocardiography. When the accuracy of the non-enhanced echocardiogram is suboptimal, it may be impossible to assess the ejection fraction accurately. Numerous factors contribute to imaging difficulties, chest wall deformities, body habitus, lung disease, and post-surgical status.  Benefits of LVO When the accuracy of the non-enhanced echocardiogram is suboptimal, it may be impossible to accurately assess left ventricular ejection fraction (LVEF) with the addition of contrast-enhancement, LVEF accuracy improves. Enhanced blood pool and endocardial borders improve the diagnostic confidence of intracardiac abnormalities such as ventricular non-compaction, hypertrophic cardiomyopathy, myocardial infarction, variants within or near the apex, ventricular aneurysm, or thrombus.    When the contrast agent microbubble is exposed to the high and low pressures of the ultrasound field, microbubbles will resonate, rapidly increasing and decreasing in size creating a large amount of acoustic backscatter. Learn more below. Response of CEA Learn about the microbubble response. Slide NumberText BlocksCalloutsAudio ScriptImage File1 The size of microbubbles is around one micron to five microns in size. Microbubbles are engineered to persist in the body by using a low molecular weight gas core surrounded by a flexible shell.  The microbubble and blood cells have a similar size to red blood cells and the microbubbles can travel anywhere within the body's vascular system. Microbubble contrast agents are introduced into the bloodstream from a diluted bolus injection or by continuous infusion (IV).  When the contrast agent microbubble is exposed to the high and low pressures of the ultrasound field, microbubbles will resonate, rapidly increasing and decreasing in size creating a large amount of acoustic backscatter.The size of microbubbles range from about one micron to five microns in size. Microbubbles are engineered to persist in the body by using a low molecular weight gas core surrounded by a flexible shell. The microbubble and blood cells have a similar size to red blood cells and the microbubbles can travel anywhere within the body's vascular system. Microbubble contrast agents are introduced into the bloodstream from a diluted bolus injection or by continuous infusion (IV). When the contrast agent microbubble is exposed to the high and low pressures of the ultrasound field, microbubbles will resonate, rapidly increasing and decreasing in size creating a large amount of acoustic backscatter.2With each pulse of acoustic pressure the microbubbles of the contrast agent will begin to expand and contract within the acoustic field. The microbubble responds to each pulse of the pressure wave, getting smaller during the compression and larger during the rarefraction of the pressure wave. When the resonating bubble is exposed to higher and higher ultrasound pressures, the magnitude of expansion is greater to expand much more than it will contract.                 Compression - smaller                 Rarefraction - largerWith each pulse of acoustic pressure the microbubbles of the contrast agent will begin to expand and contract within the acoustic field. The microbubble responds to each pulse of the pressure wave, getting smaller during the compression and larger during the rarefraction of the pressure wave. When the resonating bubble is exposed to higher and higher ultrasound pressures, the magnitude of expansion is greater expand much more than it will contract.3This disproportionate expansion and contraction cycle means that bubble echoes no longer scale directly with the acoustic ultrasound transmit pressure. This irregular scaling behavior is commonly termed as non-linear and has the observable effect that echoes start to reflect harmonics – or signals at an integer multiple of the fundamental frequency.  Twice the fundamental frequency is the second-harmonic.  The harmonic echoes define the tissue boundary interfaces used for Left Ventricular Opacification. This disproportionate expansion and contraction cycle means that bubble echoes no longer scale directly with the acoustic ultrasound transmit pressure. This disproportionate scaling behavior is commonly termed as non-linear and has the observable effect that echoes start to reflect harmonics – or signals at an integer multiple of the fundamental frequency. Twice the fundamental frequency is the second-harmonic. The harmonic echoes define the tissue boundary interfaces used for LVO.4 The Mechanical Index (MI) is controlled by the Transmit Power softkey on the ACUSON Redwood ultrasound system.  MI is a unitless measure of the magnitude of the pulse pressure and describes the acoustic power emitted out into the acoustic field. The MI is the peak negative pressure of the acoustic pressure wave divided by the square root of the transmitted frequency. The ACUSON Redwood uses a Low MI setting of 0.2.  This low MI helps to maintain and optimal environment for the microbubble to maintain the non-linear behavior which is is key to imaging with the contrast agent effectively.     American Institute of Ultrasound in Medicine, Section 7--discussion of the mechanical index and other exposure parameters. J Ultrasound Med, 2000. 19(2): p. 143-8, 154-68.The Mechanical Index (MI) is controlled by the Transmit Power softkey on the Redwood Ultrasound System. MI is a unitless measure of the magnitude of the pulse pressure and describes the acoustic power emitted out into the acoustic field. The MI is the peak negative pressure of the acoustic pressure wave divided by the square root of the transmitted frequency. The Redwood uses a Low MI setting of 0.2. This low MI helps to maintain and optimal environment for the microbubble to maintain the non-linear behavior which is is key to imaging with the contrast agent effectively. 5While actively imaging, enabling Burst on the ACUSON Redwood ultrasound system will disrupt and destroy contrast microbubbles by delivering a high MI. With Burst enabled the power increases 100%.  Pressing Burst once more returns the Low MI setting (MI of 0.20) for continued contrast imaging. Bubbles will eventually breakdown, either by enabling a high MI setting or simply over time. Eventually, after a bubble has been destroyed, the gas core is reabsorbed back into the bloodstream, exchanged at the lungs and exhaled. While actively imaging, enabling Burst on the Redwood will disrupt and destroy contrast microbubbles by delivering a high MI. With Burst enabled the power increases 100%. Pressing Burst once more returns the Low MI setting (MI of 0.20) for continued contrast imaging. Bubbles will eventually breakdown, either by enabling a high MI setting or simply over time. Eventually, after a bubble has been destroyed, the gas core is reabsorbed back into the bloodstream, exchanged at the lungs and exhaled. The ACUSON Redwood ultrasound system has an intuitive touch-screen layout and streamlined workflow for LVO. In this section you will review the instrumentation that impacts the microbubble.  Additionally, we will review the instrumentation on the ACUSON Redwood ultrasound system that impact image quality for contrast-enhanced echocardiograms for LVO.   ACUSON Redwood™ Ultrasound System Review instrumentation that has an impact on the microbubble. Tab TitleTextContrast Harmonic ImagingThe ACUSON Redwood ultrasound system uses Contrast harmonic imaging (CHI). CHI is a two-pulse sequence where the second transmission is identical to the first transmission except that it is inverted.  While using CHI on the ACUSON Redwood ultrasound system during an LVO study, the tissue signal is linear while the non-linear microbubble signal from the contrast agent is augmented. Since microbubbles have strong non-linear behavior, even at lower pressures, using CHI is an ideal choice for non-linear detection of the microbubbles.  Using CHI, the pulse generation allows for increased frame rates which is a benefit for a variety clinical scenario using LVO contrast-enhancement. FrequencyFrequency The transmit frequency for LVO is a balance between achieving diagnostic image quality while maintaining bubble integrity. High frequency settings will disrupt the microbubble. On the ACUSON Redwood ultrasound system, the Frequency is optimized for LVO at Low frequency and can be see on the display, as seen below.  The Frequency soft key is found below the touch screen, as seen below.                                          PowerPower Transmit Power is kept low for contrast-enhancement LVO to maintain the bubble integrity.  When in the contrast software for LVO, the default Agent Type is Low MI.  In the Low MI setting, the Transmit Power on the ACUSON Redwood ultrasound system is optimized for an MI of 0.20.  This Low MI setting will provide enough of the non-linear acoustic signals that are strong enough for LVO contrast-enhancement.                                                                                          BurstBurst This function is found on the soft keys of the Redwood Ultrasound System when the Contrast package is activated. By activating Burst, the Transmit Power increases to 100% across the acoustic field and will destroy the microbubble. When Burst is deactivated, the MI returns Low MI setting of 0.2.                    Burst On                            Burst Off                                                  Focus - Frame RateFocus The Focus-Depth rotary key is found at the bottom right of the control panel. The intensity of the signal tends to be strongest in the field of view (FOV) at the level of a single focus.  The focused region has higher intensity and will impact the microbubble. On the ACUSON Redwood ultrasound system, utilize a single focus and place the focus near the mitral valve level or lower to reduce microbubble destruction. In this example (above) the focus caret is near 16 cm. Pulse Duration and Pulse Repetition Frequency The pulse duration and the pulse repetition frequency (PRF) will also effect the microbubble. As the PRF increases, so does the number of acoustic pulses that impact with the microbubble and this leads to bubble destruction.  Dwell Time and DopplerDwell Time  Reducing dwell time can be achieved simply by transient imaging or simply temporarily ‘freezing’ or lifting the transducer if not actively imaging during LVO.  Electrocardiographic (ECG) gating reduces the amount of dwell time by actively imaging during a portion or portions of the cardiac cycle. ECG gating is accessed from the Physio control is found on the second touch screen page. Doppler  Color Doppler and pulse wave (PW) and continuous wave (CW) spectral Doppler are convietly located on the on the control panel. Color Doppler and PW Doppler are pulsing intermittentantly and as such, do not increase the transit power but may impact pulse repetition frequency.  However, continuous wave (CW) Doppler is continuously pulsing and this will impact the microbubble and increase the pulse repetition frequency. The contrast agent within the blood pool is a much stronger reflector than blood alone. When the contrast-enhancing agent is still present, Doppler may provide an enhancement of the blood pool and an over-enhancement of the Doppler signal.   Smith, L.A., et al., Contrast agent increases doppler velocities and improves reproducibility of aortic valve area measurements in patients with aortic stenosis. Journal of the American Society of Echocardiography, 2004. 17(3): p. 247-252. Mulvagh, S. L., Rakowski, H., Vannan, M. A., Abdelmoneim, S. S., Becher, H., Bierig, S. M., ... Zoghbi, W. A. (2008). American Society of Echocardiography Consensus Statement on the Clinical Applications of Ultrasonic Contrast Agents in Echocardiography. Journal of the American Society of Echocardiography, 21(11), 1179-1201. https://doi.org/10.1016/j.echo.2008.09.009   ACUSON Redwood™ Ultrasound System Review instrumentation that has an impact on image quality. Tab TitleTextAuto TEQ™ Auto TEQ is avaliable on the touch-screen of the ACUSON Redwood ultrasound system.  The default is off, but when Auto TEQ is activated, the overall 2D gain and edge enhancement are continuously optimized in real-time within the field of view (FOV). Auto TEQ technology will not impact the microbubble. Auto TEQ on Auto TEQ offUltraArt™UltraArt™ universal imaging processing is avaliable while utilizing the contrast software on the ACUSON Redwood ultrasound system and can be selected during live scanning or after the image is frozen.   With a single touch, the 2D image is instantly optimized for different patient types. This allows quick and easy matching of the system’s acoustic DNA parameters to individual patients in the particular scanning window. Some of the settings that are optimized include Speckle, Edge, Contrast, Gain and Dynamic Range.  The effect of the parameter changes  can be seen on the touch screen display before they are applied. UltraArt universal imaging processing has four options Off, 1, 2, or 3.  Off is the natural image. A setting of 1 yields a low amount of speckle reduction and low edge enhancement. A setting of 2 is a standard speckle reduction and mid-range edge enhancement. UltraArt universal imaging processing at a setting of 3 yields a higher amount of speckle reduction and edge enhancement. Off is the default setting in contrast mode.  An UltraArt universal imaging processing setting of 2 has been selected from the touch screen in the example seen below.  UltraArt universal imaging processing settings do not impact the microbubble.  2D Gain On the ACUSON Redwood ultrasound system, the 2D gain is found intuitively on the right side of the control panel. Users can easily optimize the 2D gain to improve the epicardial contour and the brightness of the received signal from the microbubble during the LVO exam.  Time gain compensation (TGC) settings can be adjusted for attenuation and image uniformity as needed. 2D gain and TGC settings will not impact the microbubble.  Dynamic Range Dynamic Range (DR) can be found on the ACUSON Redwood ultrasound system in the soft keys near the bottom of the screen.                                    DR is a post processing tool used to optimize the grey displayed in the image. DR is read in decibels and is the largest-intensity to the lowest-intensity that can be displayed. The intensities are grouped as shades of grey between black (the lowest intensity) to white (the highest intensity).  DR settings are typically kept low for LVO studies because the subtle grey scale information from the tissue of the left ventricle is typically not the emphasis.   Optimizing dynamic range does not impact the microbubble.2D Maps and Tints 2D Tint and Map selections are avaliable from the soft keys found just below the touch screen of the ACUSON Redwood ultrasound system.   The display of the 2D display TInt and Map differ based on individual preferences and depend on the real-time display and secondary review from a stand-alone workstation display. 2D Tints and Maps are components of post-processing and do not impact the microbubble.  Cine LoopThe Clip Length will not impact contrast. The Clip Length can be optimized for the number of beats or time. Clip Length is located on the touch screen of the ACUSON Redwood ultrasound system. A Clip Length of 2 beats is seen on the example below. Clip Length can be configured within the general configuration to save either prospectively or retrospectively. Depending on the clinical need, image collection can begin early with initial visualization of contrast, at maximum LVO enhancement, and late stages of LVO. Activating the timer from the touch screen on the ACUSON Redwood ultrasound system after the administration of contrast will document contrast utilization time on each clip. . Select the link to review references used in this course.

  • Contrast
  • Bubble
  • Microbubble
  • Power
  • Mechanical Index
  • Enhancement
  • Ultrasound
  • Agent
  • Doppler
  • Harmonic Imaging