Contrast-Enhanced Echocardiography USA

Upon completion of this course, the learner will be able to: Describe some clinical indications and benefits of contrast-enhanced echocardiography for left ventricular opacification Understand the physical properties and behaviors of the microbubble within the acoustic field Relate ultrasound instrumentation that impacts the microbubble Congratulations, you have just finished the online course Contrast-Enhanced Echocardiography.  Listed below are the key points. Take time now to review the material here and in the glossary that follows before proceeding to the final assessment. Course Review Understand the physical properties and behaviors of the microbubble within the acoustic field  Relate ultrasound instrumentation that impacts the microbubble Describe some clinical indications and benefits of contrast-enhanced echocardiography for left ventricular opacification Welcome to Contrast-Enhanced Echocardiography.  This course is a high-level general overview of contrast-enhancement for echocardiography. Microbubbles provide contrast-enhancement to echocardiography. The microbubbles follow the blood stream and enhance or opacify the blood pool within the heart chambers. When clinically indicated, contrast-enhanced echocardiograms can facilitate wall motion assessment, provide diagnostic confidence that impact patients’ diagnosis and management.   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.  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. The results of using agitated saline contrast in echocardiography were reported in 1968. Early researchers observed a “cloud of echoes” after an intra-aortic injection of saline was given and recorded the results on M-mode.  This use of intravenous agitated saline contrast echocardiography (SCE) continues to be a useful tool in echocardiography and is used as an aid in mapping the blood flow path for diagnosing right to left shunt flow, congenital anomalies, persistent left superior vena cava, patent foramen ovale, intra-atrial septal defect, and detecting valvular regurgitation. Agitated saline is a microbubble, however these air bubbles that are formed by agitation are short-lived and not able to traverse the pulmonary circulation. This M-mode image is a dramatization of the effect seen. Gupta, S.K., et al., Saline Contrast Echocardiography in the Era of Multimodality Imaging—Importance of “Bubbling It Right”. Echocardiography, 2015. 32(11): p. 1707-1719 Contrast-enhanced echocardiography improves the endocardial border detection. Currently, the most common and only U.S. FDA approved the use of Contrast-enhanced echocardiography is for Left Ventricular Opacification often referred to as LVO.  In this example, the contrast-enhancing agent is enhancing 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 TitleTextLeft Ventricular Opacification 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. Food and Drug Administration (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,  two first generation CEAs were released in 1991 and 1996. Similarly, these CEAs did traverse the pulmonary circulation and improved the ultrasound intensity of the blood pool, however, these early CEA yielded a small amplitude response in the acoustic field. Later, second-generation agents were designed for greater stability and with the innovation of Harmonic imaging these second-generation CEA microbubbles oscillated and generated harmonic energy within the acoustic field. Appropriateness Contrast enhancement is appropriate to use in echocardiography for the technically difficult-to-image patient. 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 difficulty, chest wall deformities, body habitus, lung disease, and post-surgical status.   Benefits Numerous factors contribute to imaging difficulty, chest wall deformities, body habitus, lung disease, and post-surgical status. 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 significantly 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 microbubbles are 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 Microbubbles are one micron or less (around 1.0 - 5.0 micron in size) and 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 similar size 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.Microbubbles are one micron or less (around 1.0 - 5.0 micron in size) and 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 similar size 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 pressure the microbubbles of the contrast agent 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. Compression = small Rarefraction = large With each pulse of pressure, the microbubbles of the contrast agent begin to expand and contract within the acoustic field. The microbubbles respond 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 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 left ventricular opasification. 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 left ventricular opacification. 4The Mechanical Index (MI) is a unitless measure of the magnitude of the pulse pressure and describes the acoustic power emitted out into the acoustic field. The Mechanical Index is the peak negative pressure of the acoustic pressure wave divided by the square root of the transmitted frequency. A low MI helps to maintain and optimal environment for the microbubble to maintain the non-linear behavior and is key to the stability and imaging with the contrast agent effectively. In general, the MI for LOV studies is low and in the range of 0.2 - 0.5.  However, recommended Mechanical Index ranges are documented for each contrast agent and are avaliable within the manufactures Package Insert. Additionally, 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. The Mechanical Index (MI) is a unitless measure of the magnitude of the pulse pressure and describes the acoustic power emitted out into the acoustic field. The Mechanical Index is the peak negative pressure of the acoustic pressure wave divided by the square root of the transmitted frequency. A low MI helps to maintain and optimal environment for the microbubble to maintain the non-linear behavior and is key to the stability and imaging with the contrast agent effectively. In general, the MI for LVO studies is kept low to maintain bubble integrity, and an MI or 0.2 or less will provide the non-linear acoustic signals that are strong enough for LVO. However, recommended Mechanical Index ranges are documented for each contrast agent and are avaliable within the manufactures Package Insert. Additionally, 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. 5On occasion, there are clinical applications that require the microbubbles to dissipate after the contrast-enhancement data are collected. Manually increasing the MI while actively imaging will disrupt and destroy contrast microbubbles. When avaliable, selecting a 'Burst' stage will deliver a high MI burst stage that returns to the previous low MI imaging state. Microbubbles will eventually breakdown, either by high MI or simply over time. Eventually, after a microbubble has been destroyed, the gas core is reabsorbed back into the bloodstream, exchanged at the lungs and exhaled. On occasion, there are clinical applications that require the microbubbles to dissipate after the contrast-enhancement data are collected. Manually increasing the MI while actively imaging will disrupt and destroy contrast microbubbles. When avaliable, selecting a 'Burst' stage will deliver a high MI burst stage that returns to the previous low MI imaging state. Microbubbles will eventually breakdown, either by high MI or simply over time. Eventually, after a microbubble has been destroyed, the gas core is reabsorbed back into the bloodstream, exchanged at the lungs and exhaled. Some techniques and ultrasound instrumentation have a physical impact on the microbubble, and some do not. Understanding key controls, instrumentation, and recommended techniques are a requirement for the success of contrast-enhanced echocardiograms for LVO.    Primary Controls Review controls that impact on the microbubble. Tab TitleTextContrast Harmonic ImagingSince microbubbles have strong non-linear behavior, even at lower pressures, non-linear detection techniques are added to the low frequency to exploit the non-linear behavior of the microbubble. One example is Contrast Harmonic Imaging (CHI).  CHI is a two-pulse harmonic sequence where the second transmission is identical to the first transmission except that it is inverted. CHI creates a linear signal from tissue and augments the non-linear microbubble signal from the contrast agent. CHI has an advantage in that it can image at high frame rates. For contrast-enhancement there are clinical scenarios where high frame rates are required; stress echo, patients with tachycardia, or in pediatrics. For LVO exams, apply the frequency and frame rate necessary to achieve diagnostic image quality but understand the impact on the microbubble. Higher frame rates improve the characterization and detection of lesions. however, higher frame rates can contribute to more bubble destruction. High frame rates increase dwell time – the amount of time (frames) actively imaging. Using CHI, the pulse generation allows for increased frame rates which is a benefit for a variety clinical scenario using LVO contrast-enhancement. Frequency - Power - FocusFrequency Adjusting the transmit frequency for LVO is a balance between achieving diagnostic image quality while maintaining bubble integrity. The optimal harmonic frequency for the microbubble signal varies depending on the contrast agent but is generally low frequency, between 1.6 and 2.1 MHz.   Power Transmit power is kept low for contrast-enhancement LVO to maintain the bubble integrity, and an MI of 0.20 or less will provide enough of the non-linear acoustic signals that are strong enough for LVO contrast-enhancement. Higher MI harmonic imaging leads to the destruction and collapse of the bubble and is not recommended for LVO contrast-enhancement.   However, in some very difficult cases the MI will need to be increased and additional contrast may be needed for endocardial enhancement. Focus The intensity of the signal tends to be strongest in the field of view (FOV) at a single focus level.  The focused region has higher intensity and will destroy the microbubble. When utilizing a conventional focus on LVO studies, place the single focus near the mitral valve level to reduce microbubble destruction. Full focus imaging disperses the signal across the field of view without significant impact.  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 scanning. The dwell time can be reduced by freezing the image momentarily as the agent initially enters the RV, this non-imaging time will allow the agent to adequately fill the LV. Alternately, electrocardiographic (ECG) gating can preserve the contrast agent and reduce dwell time regardless of the frame rate. ECG gating reduces the amount of dwell time by actively imaging during a portion or portions of the cardiac cycle. For example, by selecting ‘end diastole,’ the transducer is actively imaging only at end diastole and not imaging during any other time. Doppler - The contrast agent within the blood pool is a much stronger reflector than blood alone. When the agent is still present, depending on the contrast agent, Doppler is an appropriate tool to use and to take advantage of the enhanced blood pool and improved signal especially for difficult jets and tight stenotic lesions. Color Doppler and pulse wave spectral 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. When Doppler is going to be part of the clinical strategy during an LVO contrast-enhanced echocardiogram, reserve Doppler interrogation until after acquiring the primary LVO data.  AdministrationAdministration, dosing, rate, and timing of the contrast-enhancing agent will impact both the microbubble and image quality. For optimal LVO, the dosing and rate may need to be adjusted to LV function.   Attenuation is caused by too much contrast-enhancement agent given all at once and can also be cause by low EF and relatively little contrast dose. This area below the orange arrow is a simple example of attenuation shadowing the tissue below the contrast agent.                                                              Swirling patterns in the apex of the heart can be caused by administration of the contrast that is too slow, an MI that is too high, or a focal zone that is near the apex. In this example from parasternal short near the apex, there is a swirling pattern observed. A single focus is placed at the apex and the field of view has been narrowed, thus increasing the frame rate.                                                                                                                        AttenuationFor optimal LVO, the dosing and rate may need to be adjusted to LV function.   In this example, there is poor LV function and swirling of the contrast agent is seen near the apex. Swirling can also be caused by low EF and relatively little contrast dose. Package Insert Contrast agents administration information are available from the local agent’s representative and within each agent’s Package Insert. Read and understand the Package Insert for information about the preparation and administration for each contrast-enhancing agent. Secondary Controls Review controls that impact image quality. Tab TitleText2D Gain 2D gain can optimize the image quality of the received signal from the microbubble. Users should optimize the overall gain to improve the epicardial contour. Time gain compensation (TGC) settings should also be adjusted for attenuation and image uniformity as needed. Gain and TGC settings used at the beginning of the contrast-enhanced study may be too low for later stages of the exam. 2D gain will not impact the microbubble.  Dynamic Range Dynamic range is read in decibels and is the largest-power to the lowest-power settings that can be displayed. The intensities are grouped as shades of grey between black (the lowest intensity) to white (the highest intensity). Dynamic range settings should be kept low for LVO studies, keeping the tissue dark because the subtle grey scale information from the left ventricle is not the emphasis.   Optimizing dynamic range does not impact the microbubble.2D Maps and Tints 2D maps and tints are components of post-processing and do not impact the microbubble. The 2D display map and tint selections differ based on individual preferences and depend on the real-time display and secondary review on the stand-alone workstation display.                                        Cine Loop The length of time that the contrast is active depends on a variety of factors—those described above. Clip length will not impact contrast. However, clip length should be optimized in preparation prior to contrast administration. Depending on the clinical need, image collection can begin early with initial visualization of contrast, at maximum enhancement, and late stages. It is ideal if the timer that can be activated at any time to appear with each cine-loop documented. Starting the timer upon the initial administration of contrast will document contrast utilization time.   In this example the clip length begins when the contrast is seen entering the right ventricle (orange arrow) and extends until the contrast is seen entering the left ventricle.   Administration Learn more about administration impact on the microbubble. Checklist TitleChecklist TypeChecklist ContentPackage InsertHTML Contrast agents administration information are available from the local agent’s representative and within each agent’s Package Insert. Read and understand the Package Insert for information about the preparation and administration for each contrast-enhancing agent. AdministrationHTML Administration, dosing, rate, and timing of the contrast-enhancing agent will impact both the microbubble and image quality. For optimal LVO, the dosing and rate may need to be adjusted to the individual patients LV function.   AttenuationHTML Attenuation is caused by too much contrast-enhancing agent given all at once. However, attenuation can also be caused by low EF and relatively little contrast dose.   This area below the orange arrow is a simple example of attenuation that is shadowing the tissue below the contrast agent.   SwirlingHTML Swirling patterns in the apex of the heart can be caused by an administration of the contrast that is too slow, an MI that is too high, or a focal zone that is near the apex.  In this example from parasternal short near the apex, there is a swirling pattern observed.  A single focus is placed at the apex and the field of view has been narrowed, thus increasing the frame rate. SwirlingHTML In this example, there is poor LV function and swirling of the contrast agent is seen near the apex. Swirling can also be caused by low EF and relatively little contrast dose.   Select to review the Glossary or References used in this course. Glossary References