Point Shear Wave Elastography (pSWE) - USA

The development of fibrosis is the liver’s reaction to disease1 which may develop into hepatocellular carcinoma (HCC), portal hypertension, and hepatic insufficiency.1, 2 The World Health Organization (WHO) reported in 2012 that 700,000 new cases of HCC arose making it the second most common cause of cancer globally.3 HCC has a grim survival rate with few patients making it beyond two years.4 Men have double the occurrence rate to women4 and up to a third of adults with chronic hepatitis infections develop either cirrhosis or HCC. This colorized computed tomography image shows the liver (green) located in the right upper quadrant.  Congratulations! You have completed the Point 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.   Select the link below to view and print your review material before proceeding to the final assessment   Download and print a copy of the detailed Course Review.   In this course you have learned to:        Describe Acoustic Radiation Force Impulse Imaging (ARFI).      Discuss the creation of shear waves.      Explain changes in shear wave velocity and elasticity with advancing liver disease. Each patient presents with their own unique set of signs and symptoms. The gold standard for diagnosing and monitoring the progression of liver fibrosis is liver biopsy. Yet there are known limitations of a liver biopsy that making it less than ideal for ongoing assessment of disease progression. Studies have shown an increase in stiffness due to liver disease, as measured with point shear wave elastography (pSWE), to be rapid, reliable and reproducible.6-8 This course focuses on changes to liver stiffness due to chronic liver damage. Upon completion of this course, you will be able to:      Describe Acoustic Radiation Force Impulse Imaging (ARFI)      Discuss the creation of shear waves      Explain changes in shear wave velocity and elasticity with advancing liver disease   We all use 2D-mode imaging to help with diagnosis using shades of gray and the presence of clinical markers, such as shadowing or enhancement. Doppler imaging, whether spectral, color, or power, provides information on the presence or absence, speed and direction of vascular flow. Elastography allows us to assess the mechanical stiffness of tissue, providing additional information towards the clinical diagnosis and care of the patient. Point shear wave elastography helps measure liver stiffness using mechanical stress.     This image shows a 2D-mode on the left dual and a color Doppler velocity (CDV) image on the right of a cirrhotic liver. Hooke’s law explains how material responds to stress and strain.9 These two terms seem similar; however, stress is how much force we apply to the tissue, while the strain is how the tissue responds. There are two types of strain detected in the creation of an elastogram, longitudinal and shear.10 Strain occurring during compression or stretching is called longitudinal, while shear occurs when tissue twists or bends.9 Learn About Elastography Principles Learn about elastography principles. Tab TitleTextYoung's ModulusYoung’s modulus provides the constant (Y) in Hooke’s law and is an integral part of elastography as the formula explains the relationship between the amount of compression (stress) and the amount tissue deforms (strain) in its axial dimension.12 Young’s modulus assumes that stress and strain are proportional and that the tissue returns to its original shape upon compression release.12Elastic Modulus12ε = L1 – Lo / Lo   ε = Strain (change in axial length) L0 = Original axial length L1 = Change in axial length We calculate the stiffness of the liver using the change in shape, size or deformation of tissue in response to the ultrasound wave.  Stress and Strain Let’s take the time to discuss the differences between stress and strain. Stress is the force exerted and strain is what happens to the tissue in response to the pressure.   Longitudinal strain is the change in length (∆L) occurring after the application of compression to tissue. Shear strain, or the modulus of rigidity, calculation is determined by tissue changes to stress (double, curved, arrow) in tissue. Shear strain occurs as a result of angular forces, such as twisting or bending.   Kilopascals Tissues with a higher shear modulus, or modulus of rigidity (less compliant to shear forces), have a higher shear wave velocity than tissues with a lower modulus of rigidity (more compliant shear forces). The resulting tissue elasticity has a unit of kilopascals (kPa). Review the animation and image explaining the creation of an ARFI pulse and how the technology helps in the clinical setting.  Learn More About ARFI. Learn more about ARFI Tab TitleTextARFI Creation The ARFI Beam This is a representation of the ARFI beam with color showing acoustic intensity: red represents the highest intensity; lighter colors represent a lower intensity. The highest tissue displacement occurs within the beam area with the highest intensity (red). Your Turn Your turn. Instructions:Flash File:HTML5 File:/content/generator/Course_90022554/pSWE-Your_Turn-V1/index.htmlPDF File: In the last section, we learned how the push pulse or compressional wave changes the shape of a mass. The result of sound interacting with anatomy, is not only in the form of reflected information, but also in the creation of waves extending laterally. Think about how waves extend from the location of an object dropped in water. These waves, called shear waves, attenuate quickly requiring the development of signal processing methods to detect the small tissue movement.13 Learn about Shear Waves Learn about shear waves. Tissue stiffness, and thus shear wave speed, also increases with progression of liver fibrosis.10 Due to the varying methods of measuring tissue stiffness in research studies, it is beneficial to report tissue stiffness in both m/s and kPa.   Download and print a copy of the Liver Elastography Using Virtual Touch Quantification: Acquisition and Reporting Reference Guide.   The Numbers The numbers. Instructions:Flash File:HTML5 File:/content/generator/Course_90022554/pSWE-The_Numbers-interaction/index.htmlPDF File: The quality of the sonographic image influences diagnosis in all imaging modes. The exam begins before the patient presents to the imaging department in the form of fasting. Clinicians position the patient, choose the imaging plane, and perform the exam using standardized methods. Imaging tips for obtaining an optimal pSWE sampling can be found on the document and on the accompanying pages.   Important! Shear wave velocities vary between manufacturers due to the use of different detecting and velocity estimation methods. Compare shear wave velocities obtained with the same Siemens general imaging ultrasound system. Learn About Sampling with pSWE Learn about sampling with pSWE. Tab TitleTextAdditional Acquisition Tips Place the patient’s right arm above head to increase rib space. Image between ribs (intercostal space). To decrease rib shadows in the image, orient transducer parallel to ribs. Adjust overall gain settings to minimize shadowing seen posterior to ribs. Use segments 5 or 8 of the liver. Apply minimal to mild compression as excessive pressure artificially elevates shear wave velocities. Position the ROI Perpendicular to liver capsule. 1.5 to 2 centimeters deep to Glisson’s capsule or 3-6 centimeters from the skin level. Lateral to the measurement area as shear waves occur within the ROI while the push pulse is lateral to the ROI.   Avoid liver anatomy such as ligaments and vessels. ​Acquire only one measurement per suspended respiration. Invalid VelocityReasons for an invalid measurement include: Removal of the transducer during acquisition sequence. Individual velocity estimates between tracking varies resulting in an unreliable measurement. Proximity to the liver capsule. Rib shadowing. Sampling non-perpendicular to the liver capsule. Inclusion of vessels in the sample area. Excessive tissue motion, such as cardiac pulsations in the tissue, disrupt the shear wave velocity. High attenuation of the signal in large patients makes it difficult for the system to show the shear wave peak consistently during propagation. Very high stiffness of the tissue that causes the shear wave velocity estimate to become difficult (velocity out of range), lowering the confidence interval.XX.XX This image shows incorrect technique for obtaining a pSWE sample in the liver. The failed measurement (box) is due to a vessel within the ROI (arrow).17 This image also has the ROI depth (8.0 cm) greater than the recommended depth to Glisson’s capsule.22Sample Depth  This image shows the ROI at the appropriate depth to the anterior Glisson’s capsule (red) as the depth is at 4.3 centimeters from the skin surface. For an optimal measurement, place the ROI within a homogeneous area of tissue deep to the liver capsule and away from structures such as vessels or ligaments.7, 18 Use a depth measurement of four to five centimeters to reliably sample segments 5/6 and 7/8 of the liver.7   Important! The displayed depth in this image is the distance from the transducer not Glisson’s capsule. Cystic StructuresCystic structures do not create shear waves due to the very low signal created by minimal axial and lateral displacement.19, 20 A similar process occurs with other structures that do not change shape such as ribs, calcified areas (micro and macro), and shadowing tumors.19-22   The display of Vs and E values of X.XX show the lack of shear wave creation and propagation. Shear waves cannot travel in fluid such as the simple cyst seen here.23   Explore the links below for the Glossary, References, and Further Reading opportunities. Glossary Glossary. Tab TitleText2D SWE to IQR2D 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 technology uses a track, push pulse, detect sequence to create a qualitative elastogram of soft tissue.   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 box – 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., stiff vs. soft) to provide information on changes due to disease.   Hooke’s law – Small changes in a tissue mass due to compression are directly proportional to the size changes due to that compression   Interquartile range (IQR) – The distance between the 75th percentile and the 25th percentile for all measurements with an assigned label.IQR/Median Ratio to Young's ModulusIQR/Median Ratio – Unitless method to find the variability between measurements.   Longitudinal wave (i.e., compression wave) – A sound wave from the transducer into the tissue and vice versa.   Mean – The mid-point of a group of measurements.   Median – The average of a group of measurements.   Point shear wave elastography (pSWE) – ARFI generation of shear wave within a fixed ROI that gives an average velocity measurement in m/s or kPa.   Region of interest (ROI) – Defined area showing sample area for obtaining shear wave data.  The user selects ROI depth and location but cannot change the size.   Shear wave – Wave produced perpendicular to the transmit pulse.   Standard Deviation (Std Dev) – Calculation for all measurements associated with the assigned label to determine the extent from the average.   Stiffness – Tissue deformation in response to force (i.e., compression, acoustic radiation force).   Young’s modulus (elasticity modulus; E) – Mathematical description of tissue elasticity when using axial compression. References / Further Reading References / further reading. Tab TitleTextReferences 1-71. Barr, R.G., Ferraioli, G., Palmeri, M.L., Goodman, Z.D., Garcia-Tsao, G., Rubin, J., . . . Levine, D. (2015). Elastography assessment of liver fibrosis: Society of Radiologists in ultrasound consensus conference statement. Radiology. 276(3): 845-861.   2. Ferraioli, G., Filice, C., Castera, L., Choi, B.I., Sporea, L., 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.   3. WHO. (2012). Liver cancer: Estimated incidence, mortality and prevalence worldwide in 2012. GLOBCAN 2012: Estimated cancer incidence, mortality and prevalence worldwide in 2012 2012; Available from: http://globocan.iarc.fr/Pages/fact_sheets_cancer.aspx.   4. Theise, N.D. (2014). Liver cancer. In Stewart, B.W. and Wild, C.P., (Eds.), World Cancer Report 2014 (pp. 403-412). Geneva: World Health Organization International Agency for Research on Cancer.   5. WHO. (2016). Hepatitis B. 2016 July 2016 [cited 2017 March 7]; Available from: http://www.who.int/mediacentre/factsheets/fs204/en/.   6. Bai, M., Du, L., Gu, J., Li, F., and Jia, X. (2012). Virtual Touch Tissue Quantification using Acoustic Radiation Force Impulse Technology: Initial clinical experience with solid breast masses. Journal of Ultrasound in Medicine. 31(2): 289-294.   7. Jaffer, O.S., Lung, P.F.C., Bosanac, D., Patel, V.M., Ryan, S.M., Heneghan, M.A., . . . Sidhu, P.S. (2012). Acoustic radiation force impulse quantification: repeatability of measurements in selected liver segments and influence of age, body mass index and liver capsule-to-box distance. The British Journal of Radiology. 85(1018): e858-e863.References 8-168. Kramer, H., Pickhardt, P.J., Kliewer, M.A., Hernando, D., Chen, G., Zagzebski, J.A., and Reeder, S.B. (2016). Accuracy of liver fat quantification with advanced CT, MRI, and ultrasound techniques: prospective comparison with MR spectroscopy. American Journal of Roentgenology. 208(1): 92-100. 9. Benson, J. and Fan, L. (2014). Understanding ARFI and new elastography quantification technologies, in Siemens Medical Solutions, USA, Inc: Mountain View, California.   10. 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.   11. Seo, J.K. and Woo, E.J. (2013). Magnetic resonance elastography. (Eds.), Nonlinear inverse problems in imaging (pp. Wes Sussex: Wiley.   12. Giordano, N.J. (2010). Harmonic motion and elasticity. (Eds.), College physics: reasoning and relationships (pp. 348-377). Belmont: Brooks/Cole.   13. Sarvazyan, A., Hall, T.J., Urban, M.W., Fatemi, M., Aglyamov, S.R., and Garra, B.S. (2011). An overview of elastography - An emerging branch of medical imaging. Current Medical Imaging Reviews. 7(4): 255-282.   14. 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.   15. Siemens. (2016). ACUSON S1000TM S2000TM S3000TM diagnostic ultrasound system instructions for use, Siemens Medical Solutions USA, Inc: Mountain View, CA.   16. 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.References 17-2317. 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.   18. Yoo, H., Lee, J., Yoon, J.H., Lee, D.H., Chang, W., and Han, J.K. (2016). Prospective comparison of liver stiffness measurements between two point shear wave elastography methods: Virtual Touch Quantification and Elastography Point Quantification. Korean Journal of Radiology. 17(5): 750-757.   19. Barr, R.G. (2015). Breast elastography. New York: Thieme.   20. 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.   21. Teke, M., Göya, C., Teke, F., Uslukaya, Ö., Hamidi, C., Çetinçakmak, M., . . . Tekbaş, G. (2015). Combination of Virtual Touch Tissue Imaging and Virtual Touch Tissue Quantification for differential diagnosis of breast lesions. Journal of Ultrasound in Medicine. 34(7): 1201-1208.   22. Zhang, F., Han, R., and Zhao, X. (2014). The value of virtual touch tissue image (VTI) and virtual touch tissue quantification (VTQ) in the differential diagnosis of thyroid nodules. European Journal of Radiology. 83(11): 2033-2040.   23. Golatta, M., Schweitzer-Martin, M., Harcos, A., Schott, S., Gomez, C., Stieber, A., . . . Heil, J. (2014). Evaluation of Virtual Touch Tissue Imaging Quantification, a new shear wave velocity imaging method, for breast lesion assessment by ultrasound. BioMed Research International. 2014: 960262. The reproduction, transmission or distribution of this training or its contents is not permitted without express written authority. 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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, 2019. 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 exercise. Note: This is not part of the final Assessment. 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