Techniques Unique to Elastography-USA
This tutorial includes a technology review, tips & tricks to improve the image, and the unique artifacts seen on the elastogram.
Successful completion of this training is eligible for American Society of Radiology Technician (ASRT) Category A continuing education units (CEU).
Upon completion of this tutorial, you will be able to: Determine methods to improve the elastogram, and Give examples of image characteristics unique to elastography. Review the differences between compression-type strain, and shear wave elastography, Summarize the importance of avoiding precompression, Congratulations! You have completed the ‘Techniques Unique to Elastography’ tutorial. Take time to review the material before you try the final quiz. Click here to view, download, and print a detailed copy of the Course Review. In this tutorial, you have: Reviewed the differences between compression-type and shear wave elastography. Summarized the importance of avoiding precompression. Determined methods to improve the elastogram. Given examples of image characteristics unique to elastography. Siemens Healthineers would like to express our appreciation to Dr. Richard G. Barr M.D., PhD. for sharing his knowledge and providing a critical review of this tutorial content. This course will help you understand methods to obtain a quality elastogram using Siemens technology. Sections include a review of elastography, problems with precompression, exam tips and tricks, and artifacts unique to elastography. 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. Select ► to continue Welcome to the Siemens ‘Techniques Unique to Elastography’ 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. To navigate through the course, please use the forward and back buttons on the lower right-hand side. You can also go directly to a chapter using the pull-down menu found in the upper left. This tutorial contains additional 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. Click ◄ for previous page Select ► to continue 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. Elastography displays the stiffness of tissue both normal and abnormal. We know that pathology and age change tissue properties by either increasing or decreasing tissue stiffness. In breast, tissue decreases in stiffness due to fatty replacement,1 while in the case of muscle, age results in stiffness increases.2 Chronic disease such as liver fibrosis and vascular arteriosclerosis also change tissue.3 In the case of a focal lesion in the breast or thyroid, a stiff mass usually raises suspicion for a malignant process.4-6 A detailed description of elastography principles is beyond scope of this tutorial; however, the following sections give a high-level review of the basic concepts. You will see discussions of Hooke’s law and Young’s modulus (elastic modulus). Though the formulas appear complicated, they simply explain, in mathematical form, how tissue responds to compression. Hooke’s law explains how material, such as a spring, responds to stress and strain.7 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 occurring during compression, longitudinal and shear.8 Strain occurring during compression or stretching is called longitudinal while shear occurs when tissue twists or bends.7 The same ideas allow the creation of the elastogram that maps tissue response to the application and release of axial compression. Click the icon below to learn more about elastography. Learn more about Elastography Learn more about Elastography Tab TitleTextThe FormulasHooke’s law as it pertains to elastography.9 σ = Yε σ = How much axial compression (stress) Y = Numerical constant (Young’s Modulus) ε = Axial change in the targeted anatomy (strain) Young’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.10 Young’s modulus assumes that stress and strain are proportional and that the tissue returns to its original shape upon compression release.10 Young’s modulus (Elastic Modulus or E).10 ε = L / ∆L ε = Strain (change in axial length) L = Original axial length ∆L = Change in axial length When complete, select the X in the upper-right corner to close the window and continue. Tissue Stiffness The graphic on the left shows imaging of normal tissue with the same stiffness during compression. The right graphic shows how minimal compression provides the stress needed to determine the mechanical tissue properties. Stiffer tissue compresses less (loose coil) while softer tissue compresses more (tight coil). The ultrasound system then converts this change to the color or black and white scale overlay on the elastogram. When complete, select the X in the upper-right corner to close the window and continue. The elastogram provides us with information on how tissue responds to stress. This can be in the form of manual or longitudinal wave compression. The result of longitudinal waves interacting with the targeted anatomy is not only in the form of reflected information but also in the creation of shear waves extending laterally. The following sections will help you understand the similarities and differences between the four types of elastography seen on Siemens ultrasound systems. Though presented separately, examinations often use multiple elastography methods. These sections give a high-level view of technologies. For detailed explanations view the additional elastography documents included in the tutorial. Strain elastography or eSie Touch™ elasticity imaging displays tissue changes due to mechanically induced force.8, 11 Patient respiration or cardiovascular pulsations provide sufficient compression11 for the ultrasound system to create the elastogram when using a Siemens ultrasound system. The resulting strain displays in the user-selected color-coded hues called the strain or strain rate.8 Remember - this type of elastography displays stiffness relative to the surrounding tissue.12 This is a qualitative method of determining tissue stiffness utilizing compression across the entire region of interest (ROI),4 which is also known as an elasticity box (EB).13 The sonographer can increase or decrease the size of the elasticity box. Click the icon below to learn more about eSie Touch elasticity imaging. Learn More about the Elastogram Learn More about the Elastogram Tab TitleTexteSie Touch elasticity imaging This image, created using an elastography tissue phantom, shows the application of a red to blue color scale as shown by the color bar found on the left. Always check the color bar before determining tissue stiffness as there is no standard display method.8 This results in different hue assignments between manufacturers and users. This image uses red for soft areas, green for intermediate stiffness, while blue shows stiff areas. The hyperechoic mass on the left dual images as blue on the right-sided elastogram. This shows that the mass is stiffer than the surrounding area. The anechoic area on the left dual images as red on the elastogram showing it is softer than the surrounding tissue. When complete, select the X in the upper-right corner to close the window and continue. Quality Factor (QF) The strain elastogram displays stiffness relative to the surrounding tissue. Since we do not know the amount of compression used to create the image, we cannot assign a number. This qualitative method of tissue stiffness has a color assignment of either soft (SF) or stiff (HD) as shown by the color bar. A clue to the quality of the image is the QF value. The Quality Factor helps us determine the amount of motion between frames. To ensure a good image, the recommended value is above 50.14 Important! Soft and stiff color assignment changes depending on the selected map. Always check the color bar to find tissue color designations. When complete, select the X in the upper-right corner to close the window and continue. .Each crystal of the linear array transducer sends a sound beam into tissue at a specific time. After sending, the transducer then ‘listens’ for the return signal.15 Acoustic radiation force impulse or ARFI elastography works very much in the same manner. Called a ‘push pulse’, ARFI uses a group of focused crystals to create a high-intensity signal resulting in an area of tissue deformation3, 16 The transducer then tracks axial tissue displacement caused by the compressional wave.16 ARFI directs the push pulse to a specific area within the size adjustable elasticity box.4, 7 Download and print a copy of the 'Understanding ARFI and New Elastography Quantification Technologies' white paper. Click on the icon below to see examples of Siemens use of ARFI to create an elastogram. Learn More about ARFI Learn More about ARFI Tab TitleTextARFI Creation This graphic shows the method of creating an image with ARFI. A reference pulse fires to acquire data before the push pulse. The focused push pulse displaces the tissue while another tracking beam detects tissue displacement. This sequence - reference pulse, push pulse, track - repeats throughout the elasticity box.3, 16, 17 A major benefit of using a push pulse is the ability to maximize tissue displacement at a focused region.7 When complete, select the X in the upper-right corner to close the window and continue. VTiVirtual Touch™ imaging or VTi is a unique Siemens feature that uses ARFI to create a displacement, strain, qualitative elastogram.3, 4 This image of a calcified thyroid mass uses VTi to determine tissue stiffness. The black & white scale bar, found on the left of the image, shows soft tissue as white and stiff tissue as black. Similar to strain elastography, VTi shows the relative changes in tissue stiffness.3 Though we now know the amount of stress applied by the push pulse, VTi is a qualitative method of creating the elastogram.3 This is the same calcified thyroid mass using displacement color-coding. The color bar shows that soft tissue has a blue color hue while stiff tissue has a red color hue. The strong posterior shadowing seen on the left 2D-mode image (red arrow) has a color hue like the mass on the elastogram (black arrow).4, 37 The shadow function (yellow line) allows comparison measurements between the 2D-mode and elastogram. Note: VTi availability depends on the transducer, application, and system. VTi automatically activates with the selection of the appropriate parameters. When complete, select the X in the upper-right corner to close the window and continue. In the last section, we learned how the push pulse or compressional wave changes the shape of a mass. Both a strain and ARFI elastogram show changes relative to the surrounding tissue, ignoring waves created laterally to the targeted anatomy. These waves, called shear waves, attenuate quickly requiring development of signal processing methods to detect the small tissue movement.17 Download and print a copy of the 'Tissue Strain Analysis: A Complete Ultrasound Solution for Elastography' white paper. Click the icon below to learn more about shear waves. Learn More about Shear Waves Learn More about Shear Waves Tab TitleTextThe Mechanics The focused push pulse used in ARFI imaging (down arrow) compresses the targeted structure. When this area changes shape axially, it also changes horizontally (side arrows) creating shear waves.3 The system sends a signal (down arrow) to detect (arrow up) the shear wave created by tissue movement and the ARFI push pulse.4, 18 The system calculates the shear wave velocity from the returning data. Virtual Touch™ Quantification or VTq is one Siemens technology that uses point shear wave velocity measurements to calculate the speed of the transverse waves. Shear waves, like longitudinal waves, propagate differently in soft and stiff tissue. The speed of the waves, help the clinician determine the stiffness of the targeted anatomy.19 Displayed as meters per second (m/s) or as the derived Young’s modulus (kilopascals or kPa), this wave velocity becomes important when separating normal from abnormal tissues. For example: multiple studies show that shear waves in malignant breast masses tend to have a higher speed than benign masses.13, 19 Tissue stiffness, and thus shear wave speed, also increases with progression of liver fibrosis.13 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 using a simple conversion formula. VTi is a displacement image using ARFI as a qualitative method of producing the elastogram. ARFI also produces shear waves allowing quantification of tissue stiffness which is the method used in VTq3, 4 When complete, select the X in the upper-right corner to close the window and continue. m/s to kPa VTq measurements are the average shear wave speed within the ROI (green box).3, 11 This image of a liver hemangioma using VTq to find stiffness shows a velocity value of 1.10 m/s (arrow). To convert to kPa simply place the value into the following formula:4 kPa = 3Vs2 = 3(1.10)2 = 3(1.21) = 3.63 Important! This formula assumes a tissue density of 1. When complete, select the X in the upper-right corner to close the window and continue. kPa to m/s This image of the liver displays both Vs and elastic modulus (E) removing the need for a conversion. If you need to convert to m/s or Vs to kPa, simply use the following formula: Vs = √ (kPa / 3) = √ (3.6 / 3) = √ (1.2) = 1.1 When complete, select the X in the upper-right corner to close the window and continue. Point QuantificationPoint shear wave speed measurements result in an average stiffness value obtained within an ROI.3 This is what we see using VTq in the liver20 when obtaining point measurements within soft tissue (i.e., breast).8 Point quantification restricts the area sampled and the user cannot change the ROI size. Placement of the ROI 1.5 to 2 centimeters deep to Glisson’s capsule helps avoid reverberation and stiffness found close to the capsule.20, 21 This image shows incorrect technique for obtaining a VTq measurement in the liver. The failed measurement (box) is due to a vessel within the ROI (arrow).21 This image also has the ROI deeper than the recommended depth to Glisson’s capsule.22 This image shows the ROI too close to the anterior Glisson’s capsule (red) as the depth is at 2.6 centimeters from the skin surface. For an optimal measurement, place the ROI within a homogeneous area of tissue deep to the liver capsule and structures such as vessels or ligaments.20, 22 Use a depth measurement of four to five centimeters to reliably sample segments 5/6 and 7/8 of the liver.22 Important! The displayed depth is the distance from the transducer not Glisson’s capsule. When complete, select the X in the upper-right corner to close the window and continue. You may have noticed that the VTi elastogram (axial displacement using ARFI) displayed a color overlay while the VTq image displayed tissue velocity (shear wave only). A separate Siemens feature called Virtual Touch™ IQ or VTIQ is the combination of the 2D shear wave color overlay and the ability to perform multiple point shear-wave measurements at various locations within the image.13, 19 Important! To ensure high signal-to-noise ratio and reliable shear wave detection, use the Quality map. The green areas of the Quality image show adequate shear wave amplitude and signal-to-noise ratio which results in reliable measurements. Click the icon below to learn more about VTIQ. Learn More about VTIQ Learn More about VTIQ Tab TitleText2D SWE This is a color-coded shear wave elastogram or 2D SWE image of the thyroid using the VTIQ velocity mode.13 The color-coded display assigns a color to tissue stiffness based on shear wave speed in m/s. Looking at the color bar (enlarged on the left) we see that the faster shear wave speed has a color assignment of red showing stiffer tissue with the greatest velocity of 6.5 m/s. The slowest shear wave speed has a color assignment of blue with a least velocity of 0.5 m/s. Increasing or decreasing the scale allows for display of the desired shear wave speeds. When complete, select the X in the upper-right corner to close the window and continue. Point Quantification The same VTIQ image of the thyroid includes point quantification measurements (small boxes) within the 2D SWE elasticity box showing normal thyroid tissue and the mass. The Vs displays the point quantification values within the mass with a faster shear wave velocity of 2.48 m/s than the surrounding tissue of 1.75 and 1.68 m/s. This indicates the mass has a faster shear wave velocity and thus stiffer than the adjacent sampled areas.4 When complete, select the X in the upper-right corner to close the window and continue. Quality Map This elastogram shows a BI-RADS® 5 Intraductal Carcinoma using VTIQ. Point shear wave elastography (pSWE) measurements show high velocities in the peripheral areas coded as red (Vs = 6.49 m/s and 5.45 m/s). The central part measures as a low velocity with softer regions coded as green (Vs = 2.85 m/s and 2.77 m/s). The Quality map writes down that while the lesion periphery displays green (high quality), the lesion center displays orange and red, showing low shear wave quality. The green, yellow, or red color mapping simply tells us the quality of the shear waves rather than stiffness measurements. If the quality map has a yellow or red hue, the results should not be used in diagnosis. When complete, select the X in the upper-right corner to close the window and continue. The following table summarizes the forms of elastography seen within the clinical setting. Feature Name Elastography Type Displacement Method Qualitative / Quantitative Image information eSie Touch elasticity imaging Strain Manual Qualitative Relative tissue stiffness based on axial changes within a size adjustable elasticity box. VTi Strain ARFI VTq Shear wave Quantitative A single point measurement showing the average shear (lateral) wave velocity within a movable, size-restricted elasticity box. VTIQ Shear wave Qualitative / Quantitative Color-coded, 2D view of shear wave velocities within an adjustable ROI with multiple point measurements. Click on the icon below to review information each method of elastography imaging provides. Once you have reviewed the material, click on the right arrow to check your understanding with the Your Turn questions. Learn More about Elastograms Learn More about Elastograms Tab TitleTexteSie Touch versus VTi This image of a liver hemangioma used the 9L4 transducer, to obtain the eSie Touch elasticity image. The mass has a uniformly stiff appearance relative to the surrounding tissue. We can tell this is a qualitative image due to the lack of numerical values. The same hemangioma using VTi shows the stiffness and heterogeneity of the hemangioma. VTi does not require use of the quality factor (QF) as when using eSie Touch elasticity imaging since the system provides the compression in the form of the push pulse. This reduces the differences in compression seen with strain elastography and improves reproducability.7 When complete, select the X in the upper-right corner to close the window and continue. VTqVirtual Touch™ quantification or VTq gives a direct, quantitative method to measure tissue stiffness within a ROI. This image shows a sampling of liver hemangioma stiffness. The Vs of 1.11 m/s is the point shear wave average within the ROI.3, 11 Remember, the push pulse occurs outside of the ROI to produce the shear waves. This underscores the importance of placing the ROI away from shadowing structures, such as a rib or bowel, and use of ample gel during acquisition. Important! Shear wave values may vary among manufacturers. When complete, select the X in the upper-right corner to close the window and continue. VTIQVirtual Touch™ IQ has a characteristic appearance as the image displays both 2D SWE and pSWE. The color overlay or the 2D-SWE, displays the range of shear wave velocities, from minimum to maximum, correlating with the color scale found to the left in this image. Image courtesy of Dr. Richard G. Barr M.D., PhD Radiology Consultants, Inc, Youngstown, Ohio USA This VTIQ image of a breast mass shows multiple measurements of tissue stiffness. Each measurement has an accompanying icon (purple arrow). The average shear wave velocity within the measurement cursor displays to the right of the icon (orange arrow). When complete, select the X in the upper-right corner to close the window and continue. The ability to obtain a reproducible elastogram begins with several key factors. The first is precompression or the amount of compression applied before obtaining the elastogram data. Compression of superficial structures changes the tissue, sound wave, and shear wave interaction. Additionally, techniques used to obtain stiffness information for each elastography type influences the quality and accuracy of the resulting elastogram. Longitudinal waves change tissue on a molecular level.15 The wave propagation speed changes with tissue density and we use these variations to create the 2D-mode image. Using the Young’s modulus, we also know that as tissue density increases so does the stiffness.23 During the ultrasound exam, we can change the tissue density in superficial structures by the amount of pressure applied while scanning.4 Precompression occurs before obtaining stiffness information changing the quality of the resulting elastogram. Click on the information icon to learn more about precompression. Learn More about Precompression Learn More about Precompression Tab TitleTextStiffness versus CompressionThis graphic demonstrates stiffness changes from minimal compression to significant compression for various types of tissue. Tissue types have different stiffness with minimal compression (left graph). Significant compression (right graph) results in similar tissue stiffness regardless of tissue type. Minimal Compression Precompression (Tissue Strain) Significant Compression Cancer Fast Fibroadenoma Shear Wave Speed Fibroglandular Slow Fat Less More When complete, select the X in the upper-right corner to close the window and continue. Relative StiffnessFor strain elastography, where the image displays stiffness relative to surrounding tissue, precompression decreases the differences4 making all tissues stiffer. 24, 25 Thus, the resulting color-coding may not reflect the true tissue characteristics. This is due to conversion of a soft to stiff lesion or reducing the contrast between a mass and surrounding tissue.25 For example: a soft tissue such as fat becomes stiff with excessive compression.26 In the case of shear wave elastography, increasing precompression increases the shear wave velocity in both normal and abnormal tissues.4, 26-28 Important! Tissue types, such as fatty versus fibrotic tissue, increase in stiffness with increasing compression.4 When complete, select the X in the upper-right corner to close the window and continue. What amount of compression gives the best elastography while avoiding precompression? Multiple studies resulted in the development of a method to calculate compression using depth changes of a stable structure such as a rib or Coopers ligament in the breast,4, 26 or in a thyroid nodule.28 The first step in determining precompression is to image the reference structure with minimal transducer compression. Applying pressure moves the structure anterior. These two measurements, when used in the proposed formula, result in the amount of compression. Click on the information icon to learn more about calculating precompression. Calculating Compression Calculating Compression To find the amount of compression, begin by finding a structure deep in tissue. Decrease compression by lifting the transducer, barely keeping contact. In the left graphic, the reference structure lies at 4 centimeters. Compression moves the structure anterior, decreasing the depth as seen in the right graphic. The original depth and the compressed depth help calculate the amount of compression when using the following formula: Percentage of Compression = 1 – (Compressed depth / Original depth) x 100 = 1 – (3 / 4) x 100 = 1 – (0.75) x 100 = .25 x 100 = 25 percent When complete, select the X in the upper-right corner to close the window and continue. The following series of images use a biopsy proven fibroadenoma with a surgical clip to show the effect of compression using eSie Touch elasticity imaging. These images show the effect of compression on a solid breast mass. Click on the information icon to learn more about the effects of precompression. Learn More about the Effects of Precompression Learn More about the Effects of Precompression Tab TitleTextMinimal This image demonstrates an elastogram using minimal--approximately 7-12%--compression28 while imaging the fibroadenoma (arrows). This is the same fibroadenoma (arrow) mapping tissue stiffness using color hues with blue representing stiff tissue and red soft tissue. When complete, select the X in the upper-right corner to close the window and continue. MediumMedium compression changes the stiffness of the tissue hues displayed on the elastogram. This would be equivalent to greater than 20 percent precompression.28 You can see how increasing compression decreases the fibroadenoma conspicuity on the elastogram. This is the fibroadenoma with a surgical clip using a black and white elastogram. This is the same fibroadenoma using a color overlay. When complete, select the X in the upper-right corner to close the window and continue. MaximumThese images demonstrate the use of greater than 30 percent precompression.28 The images become non-diagnostic at this compression. Due to excessive compression, most breast tissue displays as black on the elastogram, which falsely shows stiff tissue. This is the same fibroadenoma and compression level showing the results of excessive compression using color hues to show tissue stiffness. Most of the elasticity box shows dark blue showing a high signal to noise ratio and thus, a nondiagnostic elastogram. When complete, select the X in the upper-right corner to close the window and continue. We know that tissue compression increases stiffness, but did you know that compression also changes shear wave behavior?24 Shear wave velocity increases with an accompanying decrease in amplitude as we apply pressure to tissues.26 The following series of VTIQ images demonstrate shear wave velocity changes resulting from precompression.27-29 This series of elastography images use an area of scar tissue at an excisional biopsy site to show the result of different amounts of precompression. Click on the information icon to learn more about the effects of precompression when using VTIQ. Learn More about the Effects of Precompression Learn More about the Effects of Precompression Tab TitleTextMinimalThis series of elastography images use an area of scar tissue at an excisional biopsy site to show the result of different amounts of precompression. This 2D-mode image shows the scar tissue. This image of the scar tissue shows the velocity with light compression (less than 10%). The velocities show a Vs of 3.45 m/s and an elastic modulus (E) of 35.7 kPa within the scar tissue (short arrow). As a comparison, a second point sample measures fat with resulting measurements of 1.43 m/s and an E of 6.1 kPa showing the differences in tissue stiffness between the two areas (long arrow). The color velocity bar, found to the left of the image, shows the highest velocity is 6.5 m/s with the lowest velocity at 0.5 m/s. The softest tissue has a color hue of blue while the stiffest tissue has a red hue. In this image, the point quantification measurements have different depths; however, to ensure equal compression, place the ROI close to the same depth. Note: The measurement display and color velocity bar has been enlarged to ensure optimal visualization. When complete, select the X in the upper-right corner to close the window and continue. Medium This image is of the same mass using the same color velocity maximum and minimum as well as color assignment. Increasing the compression to a medium level (approximately 25%) increases the Vs and E above the greatest velocity level of 6.5 m/s (yellow text). The fat Vs increased to 2.42 m/s and the E to 17.6 kPa. Notice the posterior shadowing seen on the 2D-mode image does not change the elastography color overlay. Note: The measurement display bar has been enlarged to ensure optimal visualization. When complete, select the X in the upper-right corner to close the window and continue. Maximum Maximum compression (greater than 40%) further increases the shear wave velocities showing an increase in the stiff scar tissue (red). The fat comparison increases to a Vs of 3.28 m/s and an E of 32.3 kPa. At this level of compression breast tissue such as fibroglandular tissue, fibroadenomas, fatty tissue, and cancers have similar velocities. 24, 26, 30 These compression effects occur in the thyroid,28 parotid glands,27 and musculoskeletal structures29 when comparing normal tissue to benign or malignant masses. When complete, select the X in the upper-right corner to close the window and continue. Obtaining the optimal image requires not only technical factors but proper patient preparation. Click on the information icon for tips on creating the elastogram for superficial structures and the liver. Learn More about Creating the Optimal Elastogram Learn More about Creating the Optimal Elastogram Tab TitleTextSuperficial StructureseSie Touch Elasticity Imaging (strain) only4, 14, 21 Sustain even compression throughout the patient breathing cycle. Retain images with a QF of 50 or higher. Include some surrounding tissue to allow for display of the relative stiffness. eSie Touch Elasticity Imaging (strain) and VTIQ (ARFI + shear wave)4, 11, 13, 19, 26, 28 Obtain a good 2D-mode image. Maintain a scan plane perpendicular to the skin. Use a scan window that allows for stabilization of the transducer. Maintain a perpendicular transducer angle using the patient skin and floor as a reference. Radial transducer orientation follows the breast duct. Place your wrist and hand on the patient to help with stabilization. Avoid excessive precompression by maintaining minimal pressure from the transducer. Maintain the same imaging plane throughout image acquisition. VTq and VTIQ31 Maintain a 90-degree transducer / skin angle for increased measurement accuracy. Transducer-to-structure angles less than 50 degrees produce artificially low shear wave velocities due to loss of contact. Pay attention to the transducer angle with curved surfaces such as the breast, thyroid, or intercostal spaces. VTq breast imaging only31 Place the shear wave ROI at the periphery (edge) of a lesion when repeated measurements result in "x.xx m/s" or "x.xx kPa" in the center of the lesion.* *This result is due to low shear wave signal-to-noise ratio (SNR) found with high tissue stiffness where the excitation pulse from the transducer cannot generate enough shear wave magnitude. Important! Strain elastography displays the relative stiffness of tissue. Always check the color bar to find hues assigned to soft and stiff tissue before interpreting the elastogram. When complete, select the X in the upper-right corner to close the window and continue. LiverA large organ, such as the liver, needs slightly different techniques when obtaining elastogram data. Tips for using ARFI and shear wave in the liver (VTq)13, 21, 31, 32 Fasting between 4 – 6 hours as eating increases liver stiffness values. Position patient supine or slight left lateral decubitus. 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. Place the ROI 2 – 3 centimeters below the liver capsule. 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. Suspend breathing during acquisition (expiration optimal) to minimize vascular pressure. Acquire only one measurement per suspended respiration. Obtain 10 measurements. Additional tip when using VTIQ31 Use the Quality map to confirm adequate shear wave formation. 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 ACUSON S2000™ ultrasound system and the ACUSON S3000™ ultrasound system to the same Siemens general imaging ultrasound system. Download and print a copy of the Virtual Touch Technologies – Liver Application Technical Reference Guide. When complete, select the X in the upper-right corner to close the window and continue. The interaction of the longitudinal wave and tissue creates characteristic findings during 2D-mode we call artifacts. These include the absorption or reflection of sound resulting in shadowing or a decrease in attenuation in certain structures resulting in posterior enhancement.15 In elastography useful artifacts, such as the bulls-eye, help with diagnosis while the sliding artifact or precompression hinder the clinician. 11, 33, 34 The following sections give examples of common elastography artifacts. A simple cyst has a characteristic appearance on the 2D-mode imaging. These include a round or oval shape, smooth margins, thin echogenic walls, and an anechoic central portion. Artifacts seen without many of the post processing methods currently available (i.e., Tissue Harmonic Imaging, Spatial Compounding Plus) include posterior enhancement and refraction shadowing.1, 35 Elastography also shows specific findings when imaging cystic structures such as those found in the breast or thyroid. The cyst on eSie Touch elasticity imaging shows a characteristic bull’s eye appearance while pSWE shows an area devoid of shear wave production.4 Click on the icon below to learn about the appearance of cysts with strain and shear wave elastography. Learn More about Cyst Related Artifacts Learn More about Cyst Related Artifacts Tab TitleTextStrainFluid-filled structures appear free of echoes, or anechoic on the 2D-mode image; however, on the strain elastogram they have a characteristic bull’s-eye appearance when using a Siemens system. The stiffer cyst walls display with a darker rim on a black and white elastogram while strain noise results in the appearance of the central echo. 8 The resulting bull’s-eye appearance is a combination of the cyst wall movement, internal debris movement, and the strong reflective properties of the cyst boundaries.33, 36 This dual image shows the appearance on both a 2D-mode image (left) and black and white elastogram (right). A cyst (orange arrow) appears anechoic during 2D-mode imaging. The characteristic bull’s-eye appearance (green arrow) has a dark periphery and bright central echo. A cyst also has a bright posterior echo (open, orange arrow) on the elastogram.4 This sagittal thyroid image shows the difference between a solid mass and a cyst. The color bar shows that soft tissue is lavender while stiff tissue is red. The cyst (arrow) shows the bull’s eye artifact with a red outer rim, yellow central echo, and a lavender posterior echo. The solid mass (arrowheads) has a stiffer composition compared to the surrounding tissues. When complete, select the X in the upper-right corner to close the window and continue. Shear WaveSimple cysts do not create shear waves due to the very low signal created by minimal axial and lateral displacement.4, 11 A similar process occurs with other structures that do not change shape such as ribs, calcified areas (micro and macro), and shadowing tumors.4, 11, 37, 38 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 breast cyst seen here.24 When complete, select the X in the upper-right corner to close the window and continue. In the previous sections, we learned that cysts can have a characteristic bull’s-eye appearance (using Siemens ultrasound systems) and that precompression results in an image with enough noise to render the elastogram non-diagnostic.4 Other artifacts of note include the sliding artifact, the worm pattern (which results from precompression), and shadowing. Click on the icon below to learn about artifacts unique to strain elastography. Once you have reviewed the material, click on the right arrow to check your understanding with the Your Turn questions Learn More about Artifacts Learn More about Artifacts Tab TitleTextSlidingA lesion that moves in and out of the imaging frame, usually due to sliding of the mass or transducer, results in a thick white ring appearing as the boundary. Called a sliding artifact, this movement appears as singular or multiple rings surrounding the mass. The appearance of this artifact shows a non-invasive mass that moves easily within the imaged tissue. 4, 34 Tips to decrease the sliding artifact. 4, 39 Reposition the patient. Decrease compression. Suspend respiration. Maintain lesion position during acquisition. Image courtesy of Dr. Richard G. Barr M.D., PhD Radiology Consultants, Inc, Youngstown, Ohio USA. A thick white ring surrounding a structure (red arrows) indicates either the mass or transducer moved during acquisition.4 Another indication of between-frame movement is a quality factor or QF (yellow box) below 50.4, 14, 39 When complete, select the X in the upper-right corner to close the window and continue. WormThe lack of stiffness differences in tissue results in a characteristic image containing only noise.25 In the case of significant precompression, noise results in an image with a ‘worm pattern’.4, 34 If precompression is the cause for this artifact, simply release the transducer pressure to improve the image.34 Image courtesy of Dr. Richard G. Barr M.D., PhD Radiology Consultants, Inc, Youngstown, Ohio USA. The left side of this dual image shows a hypoechoic area within breast tissue. The right sided elastogram shows no stiffness differences due to compression of the tissue. The noisy black and white pattern obscures any diagnostic information on the elastogram.4 When complete, select the X in the upper-right corner to close the window and continue. ShadowingThe returning longitudinal wave gives the data to calculate the change in tissue shape as it relates to the stiffness of tissue. In the case of a mass with shadowing, the returning signal decreases creating the characteristic posterior anechoic area.4, 15 The amount of shadowing determines whether or not the elastogram provides additional information. In the case of minimal shadowing, the posterior border detail increases. At the other extreme, strong posterior shadowing results in a blotchy elastogram due to the lack of detectable stress and strain changes.4 The 2D-mode image on the left demonstrates a refractive shadowing (arrows)15 and an area that appears to be a shadowing artifact (asterisk). The black and white elastogram removes the refractive shadowing resulting in clear posterior boundaries.4 The secondary shadowing area increases in detail on the elastogram revealing mass extension (asterisk). When complete, select the X in the upper-right corner to close the window and continue. Explore the links below for the Glossary, References, and Further Reading opportunities. References / Further Reading References / Further Reading 1. 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. 2. Agyapong-Badu, S., Warner, M., Samuel, D., and Stokes, M. (2016). Measurement of ageing effects on muscle tone and mechanical properties of rectus femoris and biceps brachii in healthy males and females using a novel hand-held myometric device. Archives of Gerontology and Geriatrics. 62: 59-67. 3. 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. 4. Barr, R.G. (2015). Breast elastography. New York: Thieme. 5. Itoh, A., Ueno, E., Tohno, E., Kamma, H., Takahashi, H., Shiina, T., . . . Matsumura, T. (2006). Breast Disease: Clinical application of US elastography for diagnosis. Radiology. 239(2): 341-350. 6. Moon, H., Sung, J., Kim, E., Yoon, J., Youk, J., and Kwak, J. (2012). Diagnostic performance of gray-scale US and elastography in solid thyroid nodules. Radiology. 262(3): 1002-1013. 7. Benson, J. and Fan, L. (2014). Understanding ARFI and new elastography quantification technologies, in Siemens Medical Solutions, USA, Inc: Mountain View, California. 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. Seo, J.K. and Woo, E.J. (2013). Magnetic resonance elastography. (Eds.), Nonlinear inverse problems in imaging (pp. Wes Sussex: Wiley. 10. Giordano, N.J. (2010). Harmonic motion and elasticity. (Eds.), College physics: reasoning and relationships (pp. 348-377). Belmont: Brooks/Cole. 11. 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. 12. Garra, B.S. (2015). Elastography: history, principles, and technique comparison. Abdominal Imaging. 40(4): 680-697. 13. 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. 14. 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. 15. Hedrick, W. (2013). Technology for diagnostic sonography. St. Louis, MO: Elsevier. 16. Nightingale, K.R., Palmeri, M.L., Nightingale, R.W., and Trahey, G.E. (2001). On the feasibility of remote palpation using acoustic radiation force. The Journal of the Acoustical Society of America. 110(1): 625-634. 17. 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. 18. Golatta, M., Schweitzer-Martin, M., Harcos, A., Schott, S., Junkermann, H., Rauch, G., . . . Heil, J. (2013). Normal breast tissue stiffness measured by a new ultrasound technique: Virtual touch tissue imaging quantification (VTIQ). European Journal of Radiology. 82(11): e676-e679. 19. 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. 20. 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. 21. 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. 22. 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. 23. Li, Z., Du, L., Wang, F., and Luo, X. (2016). Assessment of the arterial stiffness in patients with acute ischemic stroke using longitudinal elasticity modulus measurements obtained with Shear Wave Elastography. Medical Ultrasonography. 18(2): 182-189. 24. 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. 25. Varghese, T., Ophir, J., and Krouskop, T.A. (2000). Nonlinear stress-strain relationships in tissue and their effect on the contrast-to-noise ratio in elastograms. Ultrasound in Medicine & Biology. 26(5): 839-851. 26. Barr, R.G. and Zhang, Z. (2012). Effects of precompression on elasticity imaging of the breast: development of a clinically useful semiquantitative method of precompression assessment. Journal of Ultrasound in Medicine. 31(6): 895-902. 27. Mantsopoulos, K., Klintworth, N., Iro, H., and Bozzato, A. (2015). Applicability of shear wave elastography of the major salivary glands: values in healthy patients and effects of gender, smoking and pre-compression. Ultrasound in Medicine & Biology. 41(9): 2310-2318. 28. 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. 29. Paluch, Ł., Nawrocka-Laskus, E., Wieczorek, J., Mruk, B., Frel, M., and Walecki, J. (2016). Use of ultrasound elastography in the assessment of the musculoskeletal system. Polish Journal of Radiology. 81: 240-246. 30. 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. 31. Siemens. (2016). ACUSON S1000TM S2000TM S3000TM diagnostic ultrasound system instructions for use, Siemens Medical Solutions USA, Inc: Mountain View, CA. 32. 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. 33. 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. 34. Barr, R.G. (2012). Sonographic breast elastography: a primer. J Ultrasound Med. 31(5): 773-83. 35. Carr-Hoefer, C. (2012). The breast. In Kawamura, D.M. and Lunsford, B.M., (Eds.), Diagnostic medical sonography: Abdomen and superficial structures (pp. 471-527). Baltimore: Wolters Kluwer Health | Lippincott Williams & Wilkins. 36. Fan, L., Freiburger, P., Lowery, C., and Milkowski, A. Interference and characteristic of fluid tissue in ultrasound elasticity images. in Sixth International Conference on the Ultrasonic Measurement and Imaging of Tissue Elasticity. 2007. Santa Fe, New Mexico. 37. 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. 38. 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. 39. Calvete, A.C., Mestre, J., Gonzalez, J., Martinez, E., Sala, B., and Zambudio, A. (2014). Acoustic radiation force impulse imaging for evaluation of the thyroid gland. Journal of Ultrasound in Medicine. 33(6): 1031-1040. Glossary Glossary 2D 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. 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. 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. eSie Touch elasticity imaging - The conversion of tissue strain to an elastogram using external compression and pixel correlation between image frames. Fibroadenoma – Benign mass having glandular and fibrous connective tissue, usually found in the breast. Hooke’s law – Small changes in a tissue mass due to compression are directly proportional to the size changes due to that compression Longitudinal wave (i.e., compression wave) – A sound wave from the transducer into the tissue and vice versa. 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. Precompression – Compression applied to a tissue before beginning the acquisition of elastogram data. 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. 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. 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. Virtual Touch™ imaging (VTi) – The use of ARFI technology to evaluate deep tissues providing a qualitative grayscale elastogram to relative stiffness within a user-defined ROI. Virtual Touch™ IQ (VTIQ) –Color-coding of shear wave velocities within an elasticity box combined with pinpoint quantitative measurements. Virtual Touch™ Quantification (VTq) – Pinpoint measurement (m/s and kPa) of shear wave velocity to obtain a qualitative measurement of tissue stiffness using a fixed size ROI. There is no elasticity image associated with this type of tissue stiffness measurement.
- eSie Touch elasticity imaging