ACUSON Sequoia and Sequoia Select Virtual Touch Addendum Sw Ver VA30 , VA40 , VA50

ACUSON Sequoia Product Version 1.3, 2.0, 2.5 Software Version VA30, VA40, VA50 ACUSON Sequoia Select Product Version 1.0 Software Version VA50 ©2018-2023 Siemens Medical Solutions USA, Inc. All Rights Reserved. Date of first issue: 2021-07 Date of revision: 2023-05 The following trademarks are owned by Siemens Medical Solutions USA, Inc. (hereinafter "Siemens"): ACUSON, ACUSON Sequoia, Auto TEQ, Clarify, eSieCalcs, Sequoia, TEQ, UltraArt, Velocity Vector Imaging, Virtual Touch syngo is a trademark of Siemens Healthcare GmbH. All other product names are references to third-party products and are trademarks of their respective companies. Siemens includes references to third-party products in the user documentation for informational purposes only. Siemens does not endorse third-party products referenced in the user documentation. Siemens does not assume responsibility for the performance of third-party products. Siemens reserves the right to change its products and services at any time. In addition, this publication is subject to change without notice. Manufacturer Siemens Medical Solutions USA, Inc. Ultrasound 22010 S.E. 51st Street Issaquah, WA 98029 U.S.A. Phone: +1-888-826-9702 siemens-healthineers.com

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Siemens Healthineers Headquarters Siemens Healthcare GmbH Henkestr. 127 91052 Erlangen Germany Phone: +49 9131 84-0 siemens-healthineers.com

Virtual Touch Addendum

Bias and Variability in Shear Wave Measurements Virtual Touch quantification was tested with calibrated tissue equivalent elasticity phantoms. See also: For specific information, refer to the Virtual Touch Clinical Measurements: Range and Accuracy topic in Appendix A of the Instructions for Use.

Point Shear Wave Elastography (pSWE) Reference This addendum provides additional reference information for the Point Shear Wave Elastography (pSWE) feature. See also: For additional information about the pSWE feature, refer to Chapter A6 in the Advanced Imaging Manual.

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Measurement/Phantom Reference The graphs and tables in this section characterize the pSWE performance in elastic phantoms. Results will differ for in vivo human viscoelastic tissue. Five elastic phantoms were used to characterize the pSWE performance. Data were measured using customized elasticity phantoms produced by CIRS, Inc., Norfolk, Virginia. The phantoms ranged in Elasticity (Young's Modulus) from 3 kPa to 148 kPa and were certified by the phantom manufacturer according to methods described in "Characterization of Viscoelastic Materials Using Group Shear Wave Speeds"1 and "Ultrasonic Shear Wave Elasticity Imaging Sequencing and Data Processing Using a Verasonics Research Scanner"2. The phantom certification includes a nominal shear wave speed and a 95% Confidence Interval of this shear wave speed. 1

Rouze NC, Deng Y, Trutna CA, et al. "Characterization of Viscoelastic Materials Using Group Shear Wave Speeds." IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 65(5):780–794, 2018.

2

Deng Y, Rouze NC, Palmeri ML, Nightingale KR. "Ultrasonic Shear Wave Elasticity Imaging Sequencing and Data Processing Using a Verasonics Research Scanner." IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 64(1):164–176, 2017. Phantom

Calibrated SWS (m/s)

2322.1-2R (3 kPa)

1.037

2322.1-3R (13 kPa)

1.670

2322.1-4R (18 kPa)

2.132

2322.1-5R (68 kPa)

3.818

2322.1-6R (81 kPa)

5.416

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Calibration plot

Virtual Touch Addendum

Transducer Shear Wave Speed 5C1

Example of 5C1 transducer shear wave speed versus region of interest (ROI) depth for five elastic phantoms with calibrated values.

Example of 5C1 transducer shear wave speed versus ROI lateral angle position for five elastic phantoms with calibrated values.

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4V1

Example of 4V1 transducer shear wave speed versus ROI depth for five elastic phantoms with calibrated values.

Example of 4V1 transducer shear wave speed versus ROI lateral angle position for five elastic phantoms with calibrated values.

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Virtual Touch Addendum

10L4

Example of 10L4 transducer shear wave speed versus ROI depth for five elastic phantoms with calibrated values.

Example of 10L4 transducer shear wave speed versus ROI lateral position for five elastic phantoms with calibrated values.

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DAX

Example of DAX transducer shear wave speed versus ROI depth for five elastic phantoms with calibrated values.

Example of DAX transducer shear wave speed versus ROI lateral position for five elastic phantoms with calibrated values.

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Virtual Touch Addendum

Measurement Variability and Artifacts There are a number of sources of variability in measuring shear wave speed, including: 

Measurement Location and Material Stiffness



Spatial and Temporal Sampling of Shear Waves



Shear Wave Reflection Artifacts



Transducer Angle Relative to Imaging Target



Pre-Compression of Tissue

Note: Tissue viscoelasticity is an additional source of variation not characterized in this section.

Measurement Location and Material Stiffness The following graphs characterize pSWE coefficient of variation (standard deviation divided by the mean value) in elastic phantoms as a function of depth within a phantom and the stiffness of the phantom. Ten measurements were performed to obtain the mean and standard deviation values.

Example of 5C1 transducer coefficient of variation versus ROI depth for five elastic phantoms.

Example of 4V1 transducer coefficient of variation versus ROI depth for five elastic phantoms.

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Example of 10L4 transducer coefficient of variation versus ROI depth for five elastic phantoms.

Example of DAX transducer coefficient of variation for versus ROI depth for five elastic phantoms.

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Virtual Touch Addendum

Spatial and Temporal Sampling of Shear Waves The spatial and temporal sampling of a propagating shear wave bound the maximum and minimum measurable stiffness values of an ultrasound system. Under ideal conditions, the azimuthal extent of tracking beams, the pulse repetition frequency (PRF) of the tracking pulses, and the total shear wave tracking duration limit the valid measurement range. Other factors such as the induced displacement magnitude and signal-to-noise ratio may further limit the range of stiffness values a system is able to measure. The maximum measurable stiffness is related to the PRF of the tracking pulses that sample the shear wave as it propagates away from the ARFI push. To sufficiently visualize the shear wave at all azimuthal locations, there should be a minimum of two temporal samples separating the first and last azimuthal locations: (𝑥𝑥𝑚𝑚𝑚𝑚𝑚𝑚 − 𝑥𝑥𝑚𝑚𝑚𝑚𝑚𝑚 ) , 2Δ𝑡𝑡 where 𝑣𝑣𝑠𝑠𝑚𝑚𝑚𝑚𝑚𝑚 is the maximum measureable shear wave speed, 𝑥𝑥𝑚𝑚𝑚𝑚𝑚𝑚 and 𝑥𝑥𝑚𝑚𝑚𝑚𝑚𝑚 are the maximum and minimum distances from the ARFI push used for shear wave speed estimation, respectively, and Δ𝑡𝑡 is the time between successive tracking pulses. 𝑣𝑣𝑠𝑠𝑚𝑚𝑚𝑚𝑚𝑚 ≤

The minimum measurable stiffness is bounded by ensuring that the shear wave arrives at all azimuthal locations within the tracking region of interest. Therefore, the minimum measurable shear wave speed is: 𝑥𝑥𝑚𝑚𝑚𝑚𝑚𝑚 𝑣𝑣𝑠𝑠𝑚𝑚𝑚𝑚𝑚𝑚 ≥ , 𝑡𝑡𝑚𝑚𝑚𝑚𝑚𝑚 𝑚𝑚𝑚𝑚𝑚𝑚 where 𝑣𝑣𝑠𝑠 is the minimum measureable shear wave speed, 𝑥𝑥𝑚𝑚𝑚𝑚𝑚𝑚 is the maximum distance from the ARFI push, and 𝑡𝑡𝑚𝑚𝑚𝑚𝑚𝑚 is the total tracking duration. Based on these equations and the results of system tests, the following values are the minimum and maximum measurable shear wave speeds on the ultrasound system. 𝑣𝑣𝑠𝑠𝑚𝑚𝑚𝑚𝑚𝑚

6.5 m/s

4V1

𝑣𝑣𝑠𝑠𝑚𝑚𝑚𝑚𝑚𝑚

0.5 m/s

6.5 m/s

10L4

0.5 m/s

10 m/s

0.5 m/s

15 m/s

DAX

0.5 m/s

6.5 m/s

18L6

0.5 m/s

10 m/s

Transducer 5C1

0.5 m/s

 Breast  Thyroid  General 10L4  MSK

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Shear Wave Reflection Artifacts Shear wave reflections can cause artificially low shear wave speed values when measuring the shear wave speed of a focal lesion. The stiffness difference between the lesion and background tissue can result in the reflection of shear wave energy back into the focal lesion, potentially resulting in additional peaks in the displacement profile at certain tracking locations. These peaks may be misinterpreted by the arrival time estimation algorithms resulting in an artificially low speed estimate.

Example of a focal lesion in an elastic phantom using the 10L4 transducer.

Example of resulting displacement profiles showing true and reflected peaks.

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Virtual Touch Addendum

Transducer Angle Relative to Imaging Target The relative angle between the transducer and the target of interest, both in plane (azimuth) and out of plane (elevation), can be a source of variability. Five measurements were performed while varying the angle of the transducer relative to the surface of an elastic phantom. Note: In general, use a transducer perpendicular (90 degrees) to the surface for highest measurement accuracy. Note: Maintain adequate contact with the surface to ensure highest measurement accuracy and repeatability.

Results of Out of Plane (Elevation) Transducer Angle

Example of 10L4 transducer shear wave speed versus elevation angle to the elastic phantom.

Results of In Plane (Azimuth) Transducer Angle

Example of 5C1 transducer shear wave speed versus azimuth angle to the elastic phantom.

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Pre-Compression of Tissue Due to non-linear elastic properties of tissue, the shear wave speed can increase as additional pre-compression is applied to the tissue. Experiments to demonstrate this effect were done in both phantoms and human subjects.

Results of Phantom Study Using a CIRS 059 elasticity phantom, five shear wave speed measurements were acquired across multiple pre-compression levels indicating that shear wave speed increases as compression level increases.

Example of 10L4 transducer shear wave speed versus percent pre-compression of the CIRS 059 phantom.

Results of Human Subject Study A group of five sonographers acquired five shear wave speed measurements at three operatordefined compression levels in both liver and breast. When scanning in the intercostal space, operator compression level had no significant impact on measured shear wave speed in the liver. There was an increase in estimated shear wave speed with increasing compression in breast scanning consistent with the above phantom results. Note: Minimal compression is recommended. Liver Scan

Breast Scan

Example of shear wave speed versus percent pre-compression imaging liver (5C1 transducer) and breast (10L4 transducer).

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Virtual Touch Addendum

Shear Wave Elastography (SWE) Reference This section provides additional reference information for the Shear Wave Elastography (SWE) feature. See also: Additional information about the SWE feature is located in Chapter A6 of the Advanced Imaging Manual.

Correlating SWE Maps The following illustrations provide an example of a stiff lesion in a softer background: 

The Velocity map displays the lesion as a region with elevated shear wave velocities.



The Quality map represents the lesion and background areas in green, indicating that the shear wave velocity estimates are of high signal quality.



The Displacement map represents the low displacement of the shear waves in dark blue. In SWE, high shear wave velocity and low shear wave displacement are consistent with a stiffer than normal lesion.

Example of shear wave Velocity map.

Example of shear wave Quality map.

Example of shear wave Displacement map.

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Shear Wave Velocity Low Quality Threshold in Solid Lesions The following illustrations provide an example of a stiff lesion in a softer background: 

The Quality map represents a region in the posterior of the lesion in dark orange/red, indicating the shear wave velocity estimates are of very low quality.



The Velocity map represents the same region as areas of no shear wave information; only 2D-mode information behind the shear wave map overlays is visible.

If the Quality map represents an area of low shear wave quality in light orange, shear wave velocity estimates may be inaccurate. If the Quality map represents shear wave quality in red/dark orange, shear wave velocity estimation is no longer possible because it is below the quality threshold.

Example of shear wave Velocity map.

Example of shear wave Quality map.

Example of shear wave Displacement map.

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Virtual Touch Addendum

SWE in Cystic Lesions This section provides an example of imaging a cystic lesion contained within an elasticity phantom. The SWE Velocity map displays valid shear wave speed estimates in regions around the cystic target. The SWE Quality map indicates low shear wave quality within the cystic target, corresponding to regions in the SWE Velocity map displaying only 2D-mode information. The shear wave quality in the cystic target is low because shear waves do not form or propagate in fluids.

Examples of SWE Velocity, Quality, and Displacement maps imaging a cystic lesion target contained within an elasticity phantom.

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