2D Shear Wave Elastography (2D SWE) - USA

Two-dimension shear wave elastography (2D SWE) converts tissue stiffness within a region of interest (ROI) into a qualitative color overlay.1 The first step to detecting shear wave velocity, is to use the longitudinal wave to compress the targeted tissue. Capturing the resulting lateral wave (shear) with subsequent detection waves allows measurement display in both velocity and kilopascals.2   A 2D SWE assessment allows determination of stiffness of an organ, such as the liver, breast, or thyroid, in relation to the surrounding tissue. In this image, the 2D SWE (left dual) shows a method to assess stiffness of a hypoechoic (biopsy proven fibroadenoma) area within the breast. Placement over the area of concern provides a comparison of the hypoechoic tissue stiffness to the surrounding tissue.      Congratulations! You have completed the Shear Wave Elastography online training course. Listed below are the key points that have been presented. 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 to:   Explain qualitative 2D SWE display modes ​Compare stiffness within a ROI and the surrounding tissue. Predict changes in tissue stiffness due to compression. View these instructions for information on navigating through the self-evaluation tools we call ‘Your Turns’. These questions help you gauge your understanding of key topics.  Click the icon below to view 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_90023133/navigation_instruct/index.htmlPDF File: Upon completion of this course, you will be able to:        Explain qualitative 2D SWE display modes      Compare stiffness within a ROI and the surrounding tissue      Predict changes in tissue stiffness due to compression Tissue or masses tend to resist changing shape or size and return to the original dimensions after deformation. Called elasticity, the ultrasound system uses this physical property to create an elastogram. Virtual Touch™ technologies (2D SWE) use an acoustic push pulse and detection echo within an adjustable ROI to generate a displacement map representing the relative stiffness of tissue.   For a detailed discussion of longitudinal and shear strain, download and print a copy of the Understanding ARFI and New Elastography Quantification Technologies white paper. Learn More about Waves Learn more about waves. Instructions:Flash File:HTML5 File:/content/generator/Course_90023133/SU7102_SWEsimWaves20200317/index.htmlPDF File: In either the full-screen or dual-screen format, you can apply a velocity, elasticity, quality, or displacement map to the shear wave velocity and elasticity data. Each of these settings provide additional context for evaluating and interpreting the shear wave velocity and elasticity measured results.   Undetectable or non-determinant shear wave velocities and elasticity measurements within the ROI shows only the 2D-mode data in the area. A fluid-filled cyst (left) lacks shear wave creation showing an area without data. The exception is the quality map. A major advantage of 2D SWE is the ability to superimpose the quantitative elastogram information over the 2D-mode image.3 A first step in understanding the information on the image, is to use the color bar located next to the image. Learn More about 2D SWE Display Modes Learn more about 2D SWE display modes. Tab TitleTextVelocity or ElasticityThe color bar helps us understand tissue stiffness with shear wave values lower in soft tissue and higher in stiff tissue. The velocity mode displays in milliseconds (m/s) while the elasticity mode shows values in kilopascals (kPa).   This is a color-coded a 2D SWE image of a thyroid mass using a velocity map. Displayed in milliseconds (m/s), the color bar shows stiffer tissue as red with the maximum velocity of 4.0 m/s. The slowest shear wave speed has a color assignment of dark blue with a minimum velocity of 0.5 m/s. Increasing or decreasing the scale allows for display of the desired shear wave speeds. QualityThe “red / yellow / green’ color display helps us determine the quality of the shear waves used in our measurements. Green to yellow-green hues indicate reliable shear wave estimates. Measure only in these areas. Yellow suggests a value calculated here may be unreliable. Red shows areas where we are unable to obtain data.   This Quality display is mostly green with a small area of red; place the measurement ROI in the green area to increase measurement confidence.  DisplacementDisplacement is the degree of tissue movement due to the ARFI push pulse occurring within the ROI.5 Use this display mode to help improve visualization of lesion boundaries while comparing the same area on the B-mode image.   Displacement varies with the stiffness of the imaged tissue.   The color bar displays higher tissue displacement (HI) as a lighter blue while lower tissue displacement (LO) has a darker hue.   Your Turn Your Turn Instructions:Flash File:HTML5 File:/content/generator/Course_90023133/swe-yt-01/index.htmlPDF File: The 2D SWE color overlay is a quantitative method showing tissue stiffness differences. This allows us to compare tissue stiffness with each color hue indicating a speed within set upper and lower ranges.    Many clinicians require quantitative measurements for 2D SWE. To obtain measurement data we must compare tissue stiffness within the ROI and a measurement marker.   Qualitative elastography displays the relative stiffness of tissue. Always check the color bar to identify hues assigned to tissue stiffness before interpreting the elastogram.   2D SWE Quantification 2D SWE quantification. Tab TitleTextQuantification Example 1 This image shows a single measurement, using kilopascals, of tissue within the 2D SWE ROI. The color overlay provides a quantitative representation of shear wave speed. The color bar, located to the left, indicates sampled area has the lowest stiffness at approximately 1 kPa. The measurement of the blue hued area (circle) provides the qualitative value of 3.7 kPa. The elasticity measurements reflect tissue stiffness within the circular measurement marker.  Quantification Example 2 This image of the liver post ablation of a biopsy proven hepatocellular carcinoma shows three elasticity measurements. The first measurement (centrally located) shows the ablation area with the stiffest tissue (17.1 kPa) within the ROI. Liver tissue surrounding the ablation area has a shear wave measurement of 2.1 kPa (measurement marker 2) and 8.5 kPa (measurement marker 3).  Measurements two and three indicate tissue that has less stiffness than the area within area one. The sensitivity and specificity of shear wave elastography make Virtual Touch technologies an important tool in determining tissue stiffness. Remember how our longitudinal wave compressed tissue as it propagates into the body? During elastography imaging, improper imaging techniques can contribute to compression increasing tissue stiffness. This artifactual increase, called pre-compression, increases variation in our 2D SWE measurements.5-7    Siemens recommends using minimal to mild compression. Excessive transducer pressure, inadequate patient preparation, or existing medical conditions may artificially elevate shear wave speeds resulting in unreliable measurements. Learn More about Precompression Learn more about precompression. Instructions:Flash File:HTML5 File:/content/generator/Course_90023133/SU7101_PrecompAnimation/index.htmlPDF File: Your Turn Your turn. Instructions:Flash File:HTML5 File:/content/generator/Course_90023133/swe-yt-02/index.htmlPDF File: Velocity and elasticity values provide a reliable method to measure tissue stiffness in both soft tissue (i.e., thyroid, breast) and in abdominal organs (i.e., liver).8 Proper technique includes not only appropriate patient preparation, but also scanning technique.    Use of the quality map helps confirm shear wave creation.8 When using a yellow / red hue mapping, red indicates low shear wave quality or lack of shear wave creation. Remember, the same result occurs with precompression.7 Small Parts Elastography Optimization Learn more about small parts elastography optimization.2, 6, 7, 9, 10 Checklist TitleChecklist TypeChecklist ContentOptimize the 2D-mode image.HTMLWhy? An optimal 2D technique (i.e., focal zone, depth, sector width) provides the best data for the elastogram.        Decrease your depth to fill the sector with the targeted anatomy. This may be a small change as seen with this thyroid imaged at 3.5 cm depth (left) and 4 cm (right).  Position the scan plane perpendicular to the skin.HTML Why? A 90-degree angle of incidence ensures the highest measurement accuracy. Avoid precompression.HTMLWhy? Compressing tissue may artifactually increase the shear wave speed.Use a scan window that allows for stabilization ofHTMLWhy? Movement during detection of shear waves decreases accuracy of the resulting measurements.Stabilize your arm, wrist, and hand.HTMLWhy? Holding the transducer stationary during data acquisition increases velocity measurement accuracy. Use an angle sponge to support the arm and wrist while imaging the neck. You can also use a rolled-up towel or pillow.   Maintain a relaxed grip on the transducer.HTMLWhy? Tightly gripping the transducer leads to fatigue resulting in the inability to maintain minimal compression.Observe surrounding tissue for precompressionHTMLWhy? Precompression of can result in the targeted anatomy and surrounding tissue having similar stiffness. Eliminate imaging out of plane.HTMLWhy? Movement of the mass or sampled tissue during data acquisition increases noise, thus, decreasing measurement accuracy.Place the target anatomy within the focal zone.HTMLWhy? The transducer focal zone lies between 5 – 40 millimeters in depth. The system places the ROI at the lens focus for the utilized transducer increasing measurement accuracy.  Learn More about Liver Elastography Optimization Learn more about liver elastography optimization.4, 11-13 Checklist TitleChecklist TypeChecklist ContentFasting four to six hours.HTMLWhy? Non-fasting patients may show increased shear wave speeds resulting in a false-positive diagnosis.Position patient appropriately.HTMLWhy? Position patient supine or slight left lateral decubitus with arm raised above the head. Rolling the patient moves organs and bowel gas towards the dependent side. Moving the arm above the head opens the intercostal space.    Roll the patient to their left side. Make sure to reduce your scanning reach helping to decrease arm fatigue. Hold the transducer with a loose grip. Use ample gel and a 90° transducer angle.HTMLWhy? Orient the transducer perpendicular (90°) to the skin surface. A transducer angle ≤ 50 degrees to the skin surface, or use of inadequate gel, may result in artifactually low shear wave measurements due to loss of transducer contact.                                                Orange = 90° Teal = 60° Measure segments eight or five.HTMLWhy? Obtain measurements from segments eight or five using an intercostal window. ROI placement in these segments reduces the influence of cardiac motion and aids in obtaining reproducible results.   Couinaud segments eight and five lie within the medial portion of the liver. These segments help localization of pathology during the sonographic exam during surgery. Keep in mind when imaging the liver that patient segmental anatomy varies.14 Place the ROI deep to the liver capsule.HTMLWhy? Place the ROI between 3-6 centimeters deep to the liver capsule. The subcapsular reverberation reduces by placing the ROI perpendicular and 1-2 centimeters deep to the liver capsule.   The system places the ROI at the lens focus for the utilized transducer increasing measurement accuracy. Orange – liver capsule.   Use an intercostal space.HTML Why? Use the intercostal space to image liver parenchyma and avoid large vessels, bile ducts, and rib shadows Rib shadows (orange arrows) lateral to the ROI decrease shear wave generation from the acoustic radiation force impulse (ARFI) push pulse.   Suspend respiration during acquisition.HTMLWhy? Valsalva or deep inspiration increases central venous pressure falsely increasing shear wave measurements. Instruct the patient to breath normally and momentarily stop breathing until they hear a beep. The ultrasound system automatically freezes the image, emitting a beep upon acquisition completion. Obtain 10 measurements at the same site.HTMLWhy? Multiple measurements ensure a reliable median value.   You can perform multiple 2D SWE measurements using a single acquisition. Maintain an IQR / Median ratio ≤ 0.3.HTMLWhy? This unitless value helps determine the variability between measurements. This number is a method to ensure technical quality of samples.    This report shows the IQR / Median ratio calculated from 10 samples at Site 1. Explore the links below for the Glossary, References, and Further Reading opportunities. Glossary Glossary. Tab TitleText2D - Perpendicular2D shear wave elastography (2D SWE) – The display of shear wave speed within a user adjustable ROI as a color overlay on the 2D-mode image.   Acoustic radiation force impulse imaging (ARFI) – This Siemens technology uses a track, push pulse, detect sequence to create an elastogram.   Axial – Change in shape or position from front to back.   2D-mode imaging (i.e., brightness mode, grayscale, B-mode) – Ultrasound display of the amplitude of echoes returning from the body. The higher the amplitude, the brighter the display.   Elasticity – Ability of a structure to return to its original shape after compression.   Elasticity Mode (E) – Display of shear wave velocities in kilopascals (kPa).   Elasticity ROI – Adjustable area used to obtain data to create the elastogram.   Elastogram – The image demonstrating the conversion of tissue strain.   Elastography – An imaging method to map the elastic properties of tissue (i.e., stiffness) to provide information on changes due to disease.   kPa (kilopascals) – Measure of elasticity of tissue within an ROI using shear waves.   Longitudinal wave (i.e., compression wave) – A sound wave from the transducer into the tissue and vice versa.   Perpendicular – Ninety degrees to the transmitted wave.Precompression - Velocity ModePrecompression – Compression applied to a tissue before beginning the acquisition of elastogram data.   Propagate – The transmission and movement of sound into tissue.   Region of interest (ROI) – Defined area indicating sample area for obtaining shear wave data. The user selects ROI depth, location, and size.   Shear wave – A wave traveling perpendicular to the ARFI push pulse.  Shear waves travel approximately half of the transmitted longitudinal wave. Strain – Tissue response to the application of pressure (i.e., ARFI push pulse).   Stress – Pressure applied to tissue.   Qualitative – Subjective assignment of value, in elastography we assign a hue to tissue changes as it relates to the surrounding tissue.   Quantitative – Measurement of an amount expressed as a numerical value; in elastography we measure the amount of tissue deformation.   Velocity Mode (Vs) – Measure of velocity of tissue in meters per second within an ROI using shear waves.  References / Further Reading References / Further Reading Tab TitleText1 - 81. Kyriakidou, G., Friedrich-Rust, M., Bon, D., Sircar, I., Schrecker, C., Bogdanou, D., . . . Bojunga, J. (2018).              Comparison of strain elastography, point shear wave elastography using acoustic radiation force impulse imaging      and 2D-shear wave elastography for the differentiation of thyroid nodules. PLOS ONE. 13(9): e0204095.   2.  Barr, R.G., Nakashima, K., Amy, D., Cosgrove, D., Farrokh, A., Schafer, F., . . . Kudo, M. (2015). WFUMB      guidelines and recommendations for clinical use of ultrasound elastography: Part 2: Breast. Ultrasound in      Medicine and Biology. 41(5): 1148-1160. 3. Sigrist, R.M.S., Liau, J., Kaffas, A.E., Chammas, M.C., and Willmann, J.K. (2017). Ultrasound elastography:     review of techniques and clinical applications. Theranostics. 7(5): 1303-1329.   4. Cosgrove, D., Piscaglia, F., Bamber, J., Bojunga, J., Correas, J.M., Gilja, O.H., . . . Dietrich, C.F. (2013).     EFSUMB guidelines and recommendations on the clinical use of ultrasound elastography.     Part 2: clinical applications Ultraschall in Med. 34(03): 238-253.   5. Garra, B.S. (2015). Elastography: history, principles, and technique comparison. Abdominal Imaging. 40(4):     680-697.   6. Lam, A.C.L., Pang, S.W.A., Ahuja, A.T., and Bhatia, K.S.S. (2016). The influence of precompression on elasticity     of thyroid nodules estimated by ultrasound shear wave elastography. European Radiology. 26(8): 2845-2852.   7. Barr, R.G. (2019). Future of breast elastography. Ultrasonography (Seoul, Korea). 38(2): 93-105.   8. Bamber, J., Cosgrove, D., Dietrich, C.F., Fromageau, J., Bojunga, J., Calliada, F., . . . Piscaglia, F. (2013).     EFSUMB guidelines and recommendations on the clinical use of ultrasound elastography. Part 1: basic     principles and technology. Ultraschall in Med. 34(02): 169-184.9 - 149. Cosgrove, D., Barr, R., Bojunga, J., Cantisani, V., Chammas, M.C., Dighe, M., . . . Dietrich, C.F. (2017).     WFUMB guidelines and recommendations on the clinical use of ultrasound elastography: Part 4. thyroid.     Ultrasound in Medicine & Biology. 43(1): 4-26.   10. Nakashima, K., Shiina, T., Sakurai, M., Enokido, K., Endo, T., Tsunoda, H., . . . Ueno, E. (2013).      JSUM ultrasound elastography practice guidelines: breast. Journal of Medical Ultrasonics. 40(4): 359-391. 11. Ferraioli, G., Filice, C., Castera, L., Choi, B., Sporea, I., Wilson, S.R., . . . Kudo, M. (2015).      WFUMB guidelines and recommendations for clinical use of ultrasound elastography: part 3: liver.      Ultrasound in Medicine & Biology. 41(5): 1161-1179.   12. Siemens. (2018). ACUSON Sequoia™ diagnostic ultrasound system instructions for use, Siemens       Medical Solutions USA, Inc: Mountain View, CA.   13. Gibson, R. (2016). Best practices for detecting liver fibrosis with ARFI - the application of the      ultrasound-based technique at The Royal Melbourne Hospital, Siemens Healthcare USA, Inc.:      Mountain View, CA.   14. Theise, N.D. (2014). Liver cancer, in World Cancer Report 2014 Stewart, B.W.a.W., C.P., Editor,       World Health Organization International Agency for Research on Cancer: Geneva 403-412.