eSieTouch™ elasticity imaging: What does the image tell us? - USA

Upon successful completion of this course, you will be able to:   Explain the black and white and color scaling used to create the elastogram, Differentiate between soft and stiff tissue based on image characteristics, Discuss the importance of the quality factor (QF) value, and Summarize strain elastography. This course includes a comparison of the B-mode and elastogram image, information on interpretation of the strain elastogram overlay, and the quality factor (QF). Each learning activity concludes with a quiz to test your retention of the presented content. A score of 80% or higher is required to pass the quiz. You have three attempts to pass this course. Welcome to the Siemens eSie Touch™ elasticity imaging: What Does the Image Tell Us tutorial. Before we begin, I would like to introduce myself briefly. I will be your guide to help you understand the information presented in this tutorial. During the course, I will be giving you a lot of detailed information.   Click the information icon in the lower left corner for tutorial Navigation Tips.   This tutorial has more information in the form of links placed on the page. To successfully complete this course, please view all available content.   We hope you enjoy our tutorial.  Due to varying regulatory requirements, product availability varies from country to country. Some/all of the products and/or features referred to in this module may or may not be available in your country. This course addresses an international audience of healthcare customers and cannot consider all country-specific statistics, guidelines, and regulations. It is your responsibility to understand the regulations for your country or regions.   Images and graphics used in this tutorial are for educational purposes only. They may have been modified or compressed and may not reflect the actual image quality of the system.   Selecting the ► continues this course and confirms you have read and understand this disclaimer. Increases in tissue stiffness can show the presence of disease. Using changes in tissue stiffness to diagnose disease goes back over 4000 years.1 Based on feel, or palpation, this technique depends on the clinician’s skill and subjective interpretation. A modern interpretation of palpation comes in the form of an elastogram that assigns a color value to tissue stiffness. Though palpation is still an integral part of the clinical exam, in modern medical practice, computed tomography, magnetic resonance imaging, and ultrasound help find the size and shape of anatomy;2 however, only ultrasound and MRI have the capability to create the elastogram.3    Tissue stiffness from soft to stiff4 Fat Glandular tissue Carcinoma Fibrous tissue   Traditionally, sonographers have used 2D-mode and Doppler to image organs, blood flow, and pathology. Real-time or 2D-mode creates an image based on the intensity of the returning sound, while Doppler displays movement of tissue or blood. The image has information from longitudinal waves sent into the tissue and returning to the transducer.   Elastography adds another mode that allows us to image how much tissue changes when we apply gentle pressure (strain).2 Based on the relationship of pressure (tension) and the change in mass length (extension) elasticity shows the mechanical properties of a mass.5 Tissue only needs to change by a few micrometers for us to detect shape variations. A common method to apply pressure uses a very light manual compression, often in the form of respiration or a cardiac cycle. Like persistence or frame averaging, the system samples the region of interest or ROI over time, assigning a color based on the changes between image frames.1, 4   Click on the Learn More icon to view more explanations. Learn More Learn More Tab TitleText2D Mode ImageHere we see a 2D-mode or grayscale image of a breast mass showing how different returning sound intensities convert to the brightness of the imaged organ. To describe a 2D-mode image, we use terms such as hyperechoic, hypoechoic, anechoic, or isoechoic. This type of imaging, as well as Doppler, uses longitudinal waves.4   ElastogramThis is a dual image displaying the 2D-mode image on the left side and the elastogram on the right side.  The elastogram displays the mechanical properties of tissue.5 We use terms like stiff, soft, deformation, or displacement to describe the elastogram.1 Compression elastography, or eSie Touch™ elasticity imaging uses not only the anterior to posterior, or axial changes, but also changes from one image frame to the next. This tutorial focuses on strain elastography.   Construction of the ElastogramThe construction of the elastogram begins with the system acquiring a series of images during the compression release cycle.          Before                           During                             After    compression                compression                  compression        (Time 1)                         (Time 2)                         (Time 3)                   The system then compares each region between the images estimating the axial changes or strain.8 This method allows for mapping and color assignment to tissue based on the relative strain or stiffness.2   The Formula    Elasticity (E) = - Tissue compression (Stress)                                 Axial change (Strain) To begin the exam, center over the lesion, keeping an even, minimal to light pressure with the transducer. It is important to keep the transducer perpendicular to the mass refraining from movement and application of pressure. Using more than light pressure results in precompression of the mass and thus, an inadequate elastogram.10 This method of acquisition requires only the movement from the heart or vessels with the transducer held stationary.8 The ultrasound system software then compares the amount of mass compression to the surrounding tissue.   Strain elastography is a qualitative, real-time method of color assignment with no numerical value, as we do not know exactly how much pressure we have applied with the transducer. We are assigning the gray level or color as it relates to how much the surrounding tissue compresses. That means the elastogram stiffness scale is relative to the tissue surrounding the area of interest regardless of color assignment.1   Click on the Information icon to view more explanations. Learn More about the Elastogram Learn More about the Elastogram Tab TitleTextBlack and White Scale On this image, the enlarged black and white color bar shows soft tissue as white and stiff tissue as black. The color bar to the left of the image displays the gray level assigned to each tissue stiffness. We know that stiff tissue compresses less, and displays as black with the selected scale.2 This image tells us that the biopsy-proven, hypoechoic fibroadenoma is stiffer than the surrounding tissue. You will notice that there are different shades within the fibroadenoma. This tells us that the tissue stiffness varies within the mass.  Color Scale On this image, the enlarged color bar shows blue as soft tissue while red shows stiff tissue. Yellow is a medium to stiff tissue while the green is medium to soft tissue. This image uses colors to represent tissue stiffness2 rather than black and white. This image tells us that the mass is stiffer than the surrounding tissue.   One of the keys to any type of imaging is the ability to reproduce findings, but how do you know if you have a good elastogram?   You may have noticed the QF value displayed below the elastogram. This shows the quality factor of the image and is equivalent to motion seen on the 2D-mode image. Earlier we learned that the compression elastogram displays the relative tissue stiffness using multiple frames. The QF tells us whether the image includes motion artifacts due to compression variations between the frames. A large variation between frames results in a QF value below 50. In this image, you see a QF value of 80 (box) that tells us there is minimal motion artifact. Perfect correlation would result in a score of 100. As a result, using a high QF decreases interobserver variability.12 Quality computations are a frame-by-frame analysis of a group of frames. Click on the Learn More icon to view more explanations. When you are done, you can test your understanding of these key concepts with the Your Turn questions. Learn More about the Quality Factor Learn More about the Quality Factor Tab TitleTextChange Estimate To find if there is motion on an image, the system must compare axial changes between frames on the 2D-mode image. This example shows the location of a mass on the first frame and the location of a mass on a second frame after compression. The system compares the changes (lines) in location with reference anatomy (Frame 1), determining the QF for the elastogram. If anatomy compares well, there is less motion between frames and thus, a higher QF. Little correlation results in a low QF.    Quality computations are a frame-by-frame analysis of a group of frames.10 QF Comparison     2D-mode          Elastogram   QF of 15   QF of 60     Image courtesy of to Dr. Richard G. Barr M.D., PhD Radiology Consultants, Inc, Youngstown, Ohio USA This series of images show the difference in the elastogram with a high or low QF. On the left, you see the 2D-mode image of the same mass (red arrow). The upper left shows an image with a low QF indicating a significant motion between the elastogram (upper right) and the 2D-mode (upper left) image. On the right lower image, you see an elastogram with a high QF. Compare the mass (yellow arrows) definition on the elastogram between the high and low QF images. Multiple research studies revealed that the compression elastogram gives a unique method to image the size of a mass. This work showed that a mass measuring equal to or larger on the elastogram than on the 2D-mode image have a higher probability of malignancy. A mass imaging smaller on the elastogram than with 2D-mode has an increased likelihood of being a benign process.13-15 Though the black and white or color elastography scale is still qualitative, we can compare the size between the 2D-mode image and elastogram for an elastography to 2D-mode ratio or E to B size ratio. An E to B size ratio of less than 1 is suggestive of a benign mass while a ratio above 1 is suggestive of a malignant lesion.10, 11, 13, 16, 17   The strain ratio gives an estimate of stiffness between two areas of tissue. The ultrasound system uses stiffness changes between two regions of interest or ROI to calculate a strain value.10 The strain ratio provides a quantitative value for changes occurring between the surrounding normal reference tissue ROI and the mass ROI.16 Multiple studies show a high strain ratio increases the probability of malignancy.10, 11, 16    Click on the Learn More icon to see examples of semi-qualitative measurements done with the compression elastogram. Learn More about Quantification Learn More about Quantification Tab TitleTextShadow FunctionMany of the Siemens ultrasound systems allow for the real-time, dual display of the 2D-mode and elastogram.  The Shadow function allows measurement on either side of the dual image and system replication of the measurement on the opposite side.10 This becomes important when measuring a mass that appears larger or smaller on the elastogram than on the 2D-mode image.   This is an eSie Touch elasticity image of a complex thyroid mass with the Shadow Measurement function using a black and white color scale. Soft tissue displays lighter than stiff tissue. Notice the high QF on the image showing minimal tissue movement between frames.E / B Size RatioResearch on specific sonographic characteristics of breast masses helped us understand that a stiff lesion that is taller-than-wide, grows through tissue planes, has a thick capsule, lobulations, hypoechoic appearance, and spiculations, raises suspicion for a malignant mass.6, 18, 19 In this tutorial we have focused on tissue and mass changes occurring along the beam path (axial changes). Studies using elastography found if a lesion is larger on the elastogram than on the 2D-mode image, the probability of malignancy increased.13, 17, 18 , 20 This finding led to the development of the E / B size ratio used to help evaluate breast masses. This divides the transverse measurement of the elastogram mass by the transverse measurement of the 2D-mode mass to produce a ratio.13, 17 This image shows the difference seen between breast mass size on the 2D-mode (left) image and the elastogram (right).  Most ultrasound systems calculate the ratio for you; however, you could manually calculate it by using this formula:   Ratio = Elastography image size / 2D-mode size            = 1.51 / 1.18            = 1.28 Note:  The color scale used for this image has soft tissue coded as blue and stiff tissue coded as red as shown by the color bar found to the left of the image. Size MattersWe know that compression elastography creates an image based on the relative stiffness of tissue surrounding a targeted area. A combination of stiffness hues and size comparisons help the clinician determine the probability of malignancy.   Mass Characteristics Classification Soft Mixed soft and stiff Stiff, larger on 2D-mode than elastogram Low probability of malignancy Stiff, same size on 2D-mode and elastogram Stiff, larger onthe elastogram than 2D-mode Higher probability of malignancy Summary of method to classify a breast mass using size with the correlating mass elasticity scoring category (composition).10, 13, 17, 18, 20 The image below is an example of a breast mass that images smaller on the elastogram (right) than on the 2D-mode (left) image. Examining the color bar helps us understand that the soft tissue displays white while the stiff tissue displays black. The color map shows a stiffer mass than the surrounding tissue (shown by darker hues).  There are softer areas within the mass (shown by lighter hues). To decrease the subjective assessment of size, use the Shadow Function shown in the image below. This mass is smaller on the elastogram (1.1 cm) than on the 2D-mode (1.80 cm).     The image below is an example of a mass (calipers) that images the same size on the elastogram (right) and the 2D-mode (left). This image displays the soft tissue as white and the stiff tissue as black. The color map shows a mass with stiffness comparable to the surrounding tissue.   Strain RatioThe strain ratio calculates the average stiffness of tissue using the areas within the two ROIs found within the elasticity box. When performing a strain ratio, place both ROI at the same depth to ensure equal tissue compression.10            Average between image frames                                Not within the same image   Important! The displayed value is the percentage of tissue deformation between frames (frame-to-frame differences)10 as seen on the  left diagram rather than between the two ROIs as on the left diagram. This is an image showing an automatic calculation of the strain ratio in a breast mass. To obtain the strain ratio for a breast mass, place the first ROI in the reference tissue (left ROI), typically fat, and the second in mass tissue (right ROI).13, 16, 21 Make sure tissue within each ROI has a homogeneous echo pattern. Differences display as a percentage of change between image frames. Using the information from the image, the following calculation gives the strain ratio:   Strain ratio = ROI 1 (normal tissue) / ROI 2 (abnormal tissue)                   = 1.048 / 0.036                   = 29.11   Always measure the mass first to assign the result as ROI 1. Explore the links below for the Glossary, References, and Further Reading opportunities. Glossary Glossary 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.   Color scaling – Correlation of 2D-mode image mechanical stress to a color.   Compression elastography (eSie Touch™ elasticity imaging) – The conversion of tissue strain to an elastogram using external compression and pixel correlation between image frames.   Doppler imaging – Display of motion, such as blood flow, as a spectral tracing or color mapping.   Elasticity – Ability of a structure to return to its original shape after compression.   Elastogram – The image showing 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.   Fibroadenoma – Benign mass having glandular and fibrous connective tissue. Usually found in the breast.   Interobserver variability – The difference seen between two individuals measuring the same structure.   Longitudinal wave (i.e., compression wave) – A sound wave from the transducer into the tissue and vice versa. Region of interest (ROI) – Selection of an area on the image.   Stiffness – Tissue deformation in response to force (i.e., compression, acoustic radiation force).   Strain ratio - The ratio between reference and lesion defined by two ROI. For the breast, use fat for the reference tissue and the mass as the target tissue.  For the thyroid, use muscle or normal tissue for the reference and the mass as the target.   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.   Quality Factor (QF) – Measure of movement on an elastogram between image frames. References / Further Reading References / Further Reading 1. 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.   2. Garra, B.S. (2015). Elastography: history, principles, and technique comparison. Abdominal Imaging. 40(4): 680-697.   3. 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.   4. Hedrick, W. (2013). Technology for diagnostic sonography. St. Louis, MO: Elsevier.   5. Thomas, A., Fischer, T., Frey, H., Ohlinger, S., Grunwald, J., Blohmer, U., . . . Kummel, S. (2006). Real-time elastography – An advanced method of ultrasound: First results in 108 patients with breast lesions. Ultrasound Obstet Gynecol (28).   6. Stavros, A.T. (2011). The breast. In Rumack, C.M., Wilson, S.R., Charboneau, J.W., et al., (Eds.), Diagnostic ultrasound  (pp. 773-839). St. Louis: Elsevier Mosby.   7. Matthew, D. and Rapp, C.L. (2016). Possible breast Mass. In Sanders, R.C. and Hall-Terracciano, B., (Eds.), Clinical sonography: A practical guide  (pp. 713-734). Philadephia: Wolters Kluwer.   8. Shiina, T., Nightingale, K.R., Palmeri, M.L., Hall, T.J., Bamber, J.C., Barr, R.G., . . . Kudo, M. (2015). WFUMB guidelines and recommendations for clinical use of ultrasound elastography: Part 1: Basic principles and terminology. Ultrasound in Medicine and Biology. 41(5): 1126-1147.   9. 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): 238-253.10. Barr, R.G. (2015). Breast elastography. New York: Thieme.   11. Zhi, H., Xiao, X., Yang, H., Ou, B., Wen, Y., and Luo, B. (2010). Ultrasonic elastography in breast cancer diagnosis: Strain ratio vs 5-point scale. Academic Radiology. 17(10): 1227-1233.   12. Calvete, A.C., Rodríguez, J.M., de Dios Berná-Mestre, J., Ríos, A., Abellán-Rivero, D., and Reus, M. (2013). Interobserver agreement for thyroid elastography: Value of the quality factor. Journal of Ultrasound in Medicine. 32(3): 495-504.   13. Barr, R.G. (2010). Real-time ultrasound elasticity of the breast: Initial Clinical Results. Ultrasound Quarterly. 26(2): 61-66.   14. Destounis, S., Arieno, A., Morgan, R., Murphy, P., Seifert, P., Somerville, P., and Young, W. (2013). Clinical experience with elasticity imaging in a community-based breast center. J Ultrasound Med. 32: 297-302.   15. Hall, T.J., Yanning, Z., and Spalding, C.S. (2003). In vivo real-time freehand palpation imaging. Ultrasound in Med. & Biol. 29(3): 427-435.   16. Thomas, A., Degenhardt, F., Farrokh, A., Wojcinski, S., Slowinski, T., and Fischer, T. (2010). Significant differentiation of focal breast lesions: Calculation of strain ratio in breast sonoelastography. Academic Radiology. 17(5): 558-563.   17. Barr, R.G. (2011). Strain vs. shear wave breast elastography: Competitors or allies. Ultrasound in Medicine and Biology. 37(8): S100-S101.   18. Menezes, R., Sardessai, S., Furtado, R., and Sardessai, M. (2016). Correlation of strain elastography with conventional sonography and FNAC/Biopsy. Journal of Clinical and Diagnostic Research : JCDR. 10(7): TC05-TC10.18. Menezes, R., Sardessai, S., Furtado, R., and Sardessai, M. (2016). Correlation of strain elastography with conventional sonography and FNAC/Biopsy. Journal of Clinical and Diagnostic Research: JCDR. 10(7): TC05-TC10.   19. Stavros, A.T., Thickman, D., Rapp, C., Dennis, M.A., Parker, S.H., and Sinsney, G.A. (1995). Solid breast nodules: Use of sonography to distinguish between benign and malignant lesions. Radiology. 196: 123-134.   20. Garra, B.S., Cespedes, I., Ophir, J., Spratt, S.R., Zuurbier, R.A., Magnant, C.M., and Pennanen, M.F. (1997). Elastography of breast lesions: Initial clinical results. Radiology. 202: 79-86.   21. Barr, R. (2011). The utility of the "bull's-eye" artifact on breast elasticity imaging in reducing breast lesion biopsy rate. Ultrasound Quarterly. 27(3): 151-5.   These images show a right breast mass, found at the one o’clock position 5 centimeters from the nipple.   Taken on the transverse plane, the 2D-mode image shows a mass with characteristics such as being hypoechoic, taller-than-wide, posterior shadowing (arrows), and spiculations (open arrows).6   The Color Doppler Velocity (CDV) mode image mode displays flow towards the transducer as red and yellow with flow away displayed as blue and turquoise. Taken on the transverse plane, the demonstration of flow to the mass helps separate a solid from cystic mass.6, 7 The elastogram, taken on the sagittal position, uses the shadow function to aid in mass measurements. The elastogram (right) shows the stiff tissue as a red hue and soft tissue as a pink hue. When interpreting the elastogram, always check the color scale assignment.1 To view a pdf of this content, click here. The ultrasound system converts the change, or strain, resulting from external compression to either a color or black and white scale.2 Though detecting a different physiologic process, the elastogram is similar to the CDV or Color Doppler Imaging Energy (CDE) capabilities overlay.9 In CDV, movement translates to color superimposed on the 2D-mode image as an overlay within an elasticity box .4, 9 For elastography, the mechanical changes display as the overlay.2, 8   This is the same breast mass imaged with distinct color maps. The left is the 2D-mode image, the middle uses gray hues, while the right uses color hues. Whether gray or color, the hues show stiffness relative to the surrounding tissue.   Next, we take a closer look at what the elastogram overlay tells us. Tissue appears differently depending on the surrounding tissue in both 2D-mode and elastography. Thus, the same type of tissue displays as either stiff or soft relative to the surrounding tissue in both imaging methods. For example, a fat lobule may appear stiff on an image if the surrounding tissue is softer. The opposite would be true of a fat lobule surrounded by stiffer tissue.   Remember, mass stiffness displays relative to the surrounding tissue. This first example shows fat stiffness differences using a black and white color scale, some areas of fat appear darker as slight variations in fat stiffness naturally occur. Circles show corresponding areas of fat in both the 2D-mode and elastogram image. Notice the high QF factor (red box). The importance of this number is discussed in the next section. The color map in this example shows soft tissue as dark blue and stiff tissue as red. A fat lobule lies deeper and posterior to, or within, the dense fibrous layer mimicking 2D-mode characteristics typical of fat. Compare the fat lobule coded green (arrow) to the deeper fat lobule coded blue (circle). To view a pdf of this content, click here. Congratulations! You have completed the eSie Touch elasticity imaging: What Does the Image Tell Us? tutorial. Listed below are the key points presented in this course. Take time to review the material before you continue to the final quiz.   Download and print a detailed copy of the Course Review   In this tutorial you have learned to   Summarize strain elastography. Explain the black and white and color scale used to create the elastogram. Differentiate between soft and stiff tissue based on image characteristics. Discuss the importance of the quality factor. Siemens Healthineers would like to express our appreciation to Dr. Richard G. Barr M.D., PhD. for sharing his knowledge and giving a critical review of the tutorial content. eSie Touch is a trademark of Siemens Medical Solutions USA, Inc.