©RSNA, 2015
10.1148/radiol.2015150619
Appendix E1
Glossary
Strain elastography–With this technique, an external or patient-source (respiratory or cardiac
motion) compression is applied to tissue, and the US images obtained before and after the
compression are compared. The areas of the image that are least deformed are the ones that are
the stiffest, while the most deformed areas are the least stiff. Strain elastography does not
currently play an important role in the assessment of liver fibrosis.
Shear wave elastography (SWE)–With this technique, a “push pulse” is induced in the tissue
by means of acoustic radiation force. The disturbance created by this push travels perpendicular
to the ARFI pulse through the tissue as a shear wave. Using B-mode US or tissue Doppler US to
observe the tissue displacement, the shear wave speed is calculated, and the stiffness of the
intervening tissue is estimated.
Point quantification shear wave elastography (pSWE)–This is an elasticity estimation method
used to calculate the shear wave speed generated with ARFI to provide a quantitative stiffness
estimate (which can be expressed as either speed in meters per second or the Young modulus in
kilopascals. The stiffness measurement represents the mean shear wave speed within a local
ROI.
Two-dimensional shear wave elastography (2D SWE)–This is an elasticity estimate method
used to calculate the shear wave speed generated with ARFI over a field of view. Each pixel is
color coded within the field of view on the basis of its shear wave estimate. An ROI can be
placed within the field of view to display the mean stiffness estimate (expressed either in meters
per second or kilopascals).
Acoustic radiation force impulse (ARFI)–This is a very short (<1-msec) acoustic radiation
force generated with a focused acoustic beam. The pulse is designed to generate a shear wave
perpendicular to the ARFI pulse. ARFI is the pulse type that is used to obtain the previously
described 2D SWE and pSWE measurements. The tissue displacement with ARFI can also be
used for strain elastography.
Transient elastography (TE)–A quantitative one-dimensional image of tissue stiffness is
obtained by vibrating the skin with a motor to create a passing distortion in the tissue and
creating shear waves and imaging the motion of that distortion as it passes deeper into the body
by using a one-dimensional ultrasound beam. A quantitative line of tissue stiffness data is then
displayed. Fibroscan (Echosens) is the trademark name for this device.
MR elastography–This is an elasticity imaging technique in which an external vibration device
is used to generate shear waves, with a specific pulse sequence to monitor the tissue response to
generate images of shear modulus (which is related to the Young modulus by a factor of onethird under assumptions usually made).
Trademark Names for Various Manufacturers
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Siemens
EI–Elasticity Imaging, a strain elastography technique
VTQ–Virtual Touch Quantification, a pSWE technique in which ARFI is used
VTI–Virtual Touch Imaging, a strain elastography technique in which ARFI is used to generate
stress
VTIQ–Virtual Touch Image Quantification, a 2D SWE technique in which ARFI is used
MR elastography–no trade name associated
Philips
ElastPQ–a pSWE ARFI technique
MR elastography–no trade name associated
Supersonic Imagine
Real-time shear wave elastography–a 2D SWE technique that operates in real time
GE
2D SWE–no associated trade name
MR Touch–an MR elastography technique
Toshiba
OneShot acquisition–a 2D SWE technique
Continuous acquisition–a real-time 2D SWE technique
Propagation map–the 2D SWE shear wave arrival time is presented as contour lines that can be
used as a quality measure
Conversion of Shear Wave Speed in Meters per Second to Young and
Shear Modulus
To convert the shear wave speed in meters per second to the Young modulus in kilopascals, the
following equation can be used: E = 3(vS2 · ), where E is the Young modulus, vS is the shear
wave speed, and  is the density of the tissue in homogeneous isotropic tissues. The assumption
is made that the density is 1 g/mL and that the tissue is a linear, isotropic, incompressible and
elastic soft tissue. According to these assumptions, the shear modulus (µ) in kilopascals can be
related to the Young modulus as µ = E/3.
References
1. Ferraioli G, Tinelli C, Lissandrin R, et al. Point shear wave elastography method for assessing
liver stiffness. World J Gastroenterol 2014;20(16):4787–4796.
2. Friedrich-Rust M, Nierhoff J, Lupsor M, et al. Performance of acoustic radiation force impulse
imaging for the staging of liver fibrosis: a pooled meta-analysis. J Viral Hepat 2012;19(2):e212–
e219.
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3. Ferraioli G, Tinelli C, Dal Bello B, et al. Accuracy of real-time shear wave elastography for
assessing liver fibrosis in chronic hepatitis C: a pilot study. Hepatology 2012;56(6):2125–2133.
118. Iijima H. Approaches to the diagnosis of liver fibrosis. Tokyo, Japan: Toshiba Medical
Systems Corporation, 2014.
4. Iijima H. Approaches to the diagnosis of liver fibrosis. Tokyo, Japan: Toshiba Medical
Systems Corporation, 2014.
5. Tsochatzis EA, Gurusamy KS, Ntaoula S, Cholongitas E, Davidson BR, Burroughs AK.
Elastography for the diagnosis of severity of fibrosis in chronic liver disease: a meta-analysis of
diagnostic accuracy. J Hepatol 2011;54(4):650–659.
6. LOGIQ E9 Shear wave elastography whitepaper. GE. 11/3/14 Document ID: JB23292GB.
http://www3.gehealthcare.com/en/products/categories/ultrasound/logiq/logiq_e9. Accessed April
18, 2015.
7. Venkatesh SK, Ehman RL. Magnetic resonance elastography of liver. Magn Reson Imaging
Clin N Am 2014;22(3):433–446.
Table E1. Suggested Thresholds for Elastography Measurements of Liver
Stiffness in Hepatitis C on the Basis of Published Literature for Each
Manufacturer
Liver Fibrosis
Stage
US-based Methods
||
GE (6)
MR
Elastography
(GE, Siemens,
Philips) (7)
(kPa)††‡‡
Philips (1)
(m/sec)*
Siemens (2)
(m/sec)†
SuperSonic
Imagine (3)
(m/sec)‡
Toshiba (4)
§
(m/sec)
TE (5) (kPa)
Fibrosis  2
1.22 (5.2)
1.34 (5.7)
1.5 (7.1)
NA
7.2
1.66 (8.29)
3.5
Fibrosis  3
1.49 (7.0)
1.55 (7.3)
1.7 (8.7)
NA
9.6
1.77 (9.40)
4.0
Fibrosis = 4
2.21 (12.3)
1.80 (10)
1.9 (10.4)
2.23 (15)
14.5
1.99 (11.9)
5.0
(m/sec)
#
**
Note.—Values in parentheses are in kilopascals. NA = not available.
* From reference 1.
†
‡
From reference 2.
From reference 3.
§
From reference 4, which is a publication by the manufacturer and not in the peer-reviewed
literature.
||
From reference 5.
#
From reference 6.
** Publication by the manufacturer and not in the peer-reviewed literature.
††
From reference 7.
‡‡
Sheer modulus.
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