Making Bubbles Dance - USA

This course contains information on how contrast agents aid imaging in ultrasound. We begin with a review of important basic principles. Ultrasound contrast agents are liquid-based suspensions that easily inject into the blood stream. This allows real-time visualization of the circulatory system whether it be the heart chambers or liver vascularity.1, 2 These microbubbles have a stable shell that contain the air, which, through their behavior enhance tissue visualization.1   Come along with us to see how to make the bubbles dance during our contrast enhanced ultrasound (CEUS) exams.   Congratulations! You have completed the Making Bubbles Dance course. Listed below are the key points presented in this course. Take time to review the material before you try the final assessment.   Download and print a copy of the detailed Course Review   In this course you have learned: Relate bubble destruction to the mechanical index (MI) Explain the importance of phase inversion and amplitude modulation imaging Identify how ultrasound changes the microbubble The use of scatterers, in the form of contrast agents, increases our ability to detect flow within an organ. Ultrasound contrast agents are small, gas-filled bubbles within a shell. The red blood cell, or smaller, size of a microbubble allows for travel from the venous to arterial system via the lung capillaries.3 As the bubbles expand and contract in response to the ultrasound wave, they create the needed backscatter in the form of harmonic waveforms.2-4   Long used in echocardiographic exams, contrast allows for assessment of intracardiac flow. Abdominal contrast provides vascular information for pathology with characteristic filling patterns. One step in using contrast imaging, is to understand bubble behavior and the technology used to create the ultrasound image. First, let’s review the components of a wave, the importance of the tissue / sound interaction, signal-to-noise ratio, and the mechanical index.  The same principles we use for 2D-mode imaging apply to contrast imaging. Multiple parameters become especially relevant with contrast imaging; compression and rarefication, the interaction of a longitudinal wave with tissue, the signal-to-noise ratio (SNR), and the mechanical index (MI).    To begin, review these principles. Later in the course these factors become important to maintaining or destroying the microbubble. Learn About Ultrasound Waveform Anatomy Learn about ultrasound waveform anatomy. Tab TitleTextWaveform Anatomy A conversation on microbubble behavior includes terms describing components of the waveform. Let’s begin by discussing these terms as they relate to one waveform. Keep in mind, the transmitted signal has multiple waveforms and wavelengths within the beam. We are all familiar with a single waveform that has an upward and downward part. The upward portion of the wave (double arrows) is called the positive or high-pressure part of the wave, while the downward portion is the negative or low-pressure part of the wave.1, 5  Amplitude The amplitude of the waveform is another piece we change when imaging. Defined as the highest positive or negative point on the waveform, increases result in an increase in sound ‘loudness’. Think of striking a bell multiple times, the frequency remains the same, the sound simply becomes louder. In ultrasound imaging we use decibels (dB) to measure the amplitude of the transmitted sound waves. We can change the amplitude by increasing or decreasing the transmit power.Tissue / Sound Interaction  The high-pressure part of the waveform compresses a particle while the downward movement has less compression allowing the particle to expand (rarefication). As a transmitted wave passes through the body, the cells increase and decrease in size with the upward and downward movement of the wave in an equal manner. Thus, this type of wave is referred to as a longitudinal compression wave and the particles reaction to the waves is linear because they contract and expand equally.1, 5 The longitudinal wave results in particle oscillations in the direction of propagation. In this course we assume a wave parallel to the transmitted beam into and received from the tissue.  Mechanical Index (MI) The mechanical index (MI) is the peak downward movement of the waveform (rarefication) divided by the square root of the pulse bandwidth center frequency.1, 5 This simply is the method we use to measure the formation of bubbles occurring within tissue (stable cavitation). These bubbles change size with the longitudinal wave eventually collapsing (transient cavitation).1, 2, 5    Factors that change the MI include:2, 4 Output power level (high levels cause bubbles to rupture) Transducer frequency Changes with the imaged depth Location within the beam (central beam has highest power) Dwell time in the imaging plane Learn More About Amplitude Learn more about amplitude. Instructions:Flash File:HTML5 File:/content/generator/Course_90022747/Amplitude-V0/index.htmlPDF File: Signal-to-noise ratio is a term often used to describe the quality of the ultrasound signal. Expressed in decibels (dB), this simply tells us the strength of our ultrasound wave compared to background noise. How does this change the detail of our ultrasound image?    SNR is a term used to describe both noise introduced by system electronics and tissue. This course focuses on noise created by the tissue. If the transmitted waveform and noise velocity have the same values, the SNR would be zero. That means that the noise competes with the signal resulting in unusable data. When the sent velocity increases, the SNR also increases resulting in a positive value. Our ultrasound system then uses the information to create the image. What might different SNR levels sound like? Use the interaction to help you understand how noise interferes with our ability to receive the transmitted ultrasound wave. With each noise level, listen for the birds chirping. Learn about SNR Learn more about SNR. Instructions:Flash File:HTML5 File:/content/generator/Course_90022747/SNR-V3/index.htmlPDF File: Your Turn Your Turn. Instructions:Flash File:HTML5 File:/content/generator/Course_90022747/Contrast-YourTurn-01/index.htmlPDF File: What makes bubbles special?   They resonate! Remember that longitudinal mechanical wave we talked about earlier? Bubbles also react to the waveform pressure changes by increasing and decreasing in size.2   Learn About Bubble Behavior Learn about bubble behavior. Tab TitleTextBubble and Pressure Image used with permission from Qin, S., Caskey, C.F., and Ferrara, K.W. (2009). Ultrasound contrast microbubbles in imaging and therapy: physical principles and engineering. Physics in medicine and biology. 54(6): R27. The upper image shows how the high-pressure part of the waveform results in contraction of the bubble (small bubble) while the low-pressure results in expansion of the bubble (large bubble). The bubble generates strong reflections as it resonates; however, it bursts eventually (lower). Our goal is to keep the bubble resonating as long as possible.6 Notice that the bubbles do not always compress and expand equally.Bubble Symphony    Explore the links below for the Glossary, References, and Further Reading opportunities. Glossary Glossary. Amplitude – The maximum negative or positive height of the waveform measured from zero.   Bandwidth – Range of frequencies.   Contrast agent – Any substance that enhances the contrast in blood or (fluid) filled areas of the body.    Dwell time – Time spent in the same scanning plane.   Linear scale – A scale using equal distance and values.   Longitudinal wave (i.e., compression wave) – A wave oscillation in the direction of propagation.   Mechanical index (MI) – An index which helps indicate the level of transmitted acoustic intensity. It is defined as the peak negative point divided by the square root of the center transducer frequency.   Microbubble – Encapsulated gas bubble measuring between one and ten microns.   Output power – The strength of the transmitted pulse.   Signal-to-noise ratio (SNR) – the ratio of an ultrasound pulse to interfering, often artifactual, noise. References and Further Reading References and further reading. 1.  Kremkau, F.W. (2016). Sonography: principles and instruments. 9 ed., St. Louis: Elsevier.   2.  Burns, P.N. (2011). Contrast agents for ultrasound. In Rumack, C.M., Charboneau, W., Wilson, S.R., et al., (Eds.), Diagnostic Ultrasound (pp. 53-75). Philadelphia: Elsevier Mosby.   3.  Sirsi, S. and Borden, M. (2009). Microbubble compositions, properties and biomedical applications. Bubble science engineering and technology. 1(1-2): 3-17.   4.  Perera, R., Hernandez, C., Zhou, H., Kota, P., Burke, A., and Exner, A. (2015). Ultrasound imaging beyond the vasculature with new generation contrast agents. WIREs Nanomed Nanobiotechnol. 7(4): 593-608.   5.  Hedrick, W. (2013). Technology for diagnostic sonography. St. Louis, MO: Elsevier.   6. Qin, S., Caskey, C.F., and Ferrara, K.W. (2009). Ultrasound contrast microbubbles in imaging and therapy: physical principles and engineering. Physics in medicine and biology. 54(6): R27.   7.  Stieger, S.M., Dayton, P.A., Borden, M.A., Caskey, C.F., Griffey, S.M., Wisner, E.R., and Ferrara, K.W. (2008). Imaging of angiogenesis using Cadence™ contrast pulse sequencing and targeted contrast agents. Contrast Media & Molecular Imaging. 3(1): 9-18.   8.  Wilson, S.R., Jang, H., Kim, T.K., Iijima, H., Kamiyama, N., and Burns, P.N. (2008). Real-time temporal maximum-intensity-projection imaging of hepatic lesions with contrast-enhanced sonography. American Journal of Roentgenology. 190(3): 691-695.   9.  Stolz, E.P. and Kaps, M. (2005). Ultrasound contrast agents and imaging of cerebrovascular disease. Seminars in Cerebrovascular Diseases and Stroke. 5(2): 111-131. 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.   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.   Copyright © Siemens Healthcare GmbH, 2020 Upon completion of this course, you will be able to:   Relate bubble destruction to mechanical index (MI) Explain the importance of phase inversion and power modulation imaging Identify how ultrasound changes the microbubble View these instructions for information on navigating through the self-evaluation tools we call ‘Your Turns’. Click the icon below to start the self-evaluation instructions. Note: This is not part of the final Assessment. Learn How to Navigate the Your Turns Learn how to navigate the Your Turns. Instructions:Flash File:HTML5 File:/content/generator/Course_90022747/Navigation_Instructions_Contrast/index.htmlPDF File: Our goal when creating the ultrasound contrast image is to separate the tissue signal from the unique microbubble signal. The ultrasound system software performs this function while operating at a low mechanical index. A low mechanical index exploits the highly non-linear behavior of microbubbles we learned about earlier. Your Turn Your Turn. Instructions:Flash File:HTML5 File:/content/generator/Course_90022747/Contrast-YourTurn-02-V1/index.htmlPDF File: Pulse Inversion and Power Modulation Learn more about the ultrasound signal.