Compression (SE) vs Shear Wave (SWE) Elastography: Physics, Limitations, and Method Selection
Physical Principles
Elastography measures tissue deformation after the application of external stress: softer tissues deform more than stiffer ones (ACR/SRU, 2024). There are two main types of imaging elastography — strain elastography (SE) and shear wave elastography (SWE).
SE is a qualitative method comparing the relative stiffness of tissues in the field of view (FOV). Stress can be applied by compressing and releasing the tissue with a probe, internal movement (breathing, vascular pulsation), or an acoustic impulse (ARFI) (ACR/SRU, 2024).
SWE is a quantitative method. Focused acoustic impulses cause microscopic tissue displacement, inducing perpendicular shear waves, the propagation of which is tracked sonographically. Stiffer tissues exhibit higher shear wave speeds (Hagen-Ansert, 2023). SWE measures shear wave speed (SWS) in m/s, which can be converted into stiffness (Young's modulus, kPa) (ACR/SRU, 2024).
According to EFSUMB (2019), all ultrasound elastography methods measure internal shear deformations of tissue from applied force, but the type of force is important: if the force changes slowly relative to the time it takes for the shear wave to propagate to the depth of interest (palpation by probe or physiological movement), the process is considered quasi-static. SWE includes ARFI-based techniques and transient elastography (TE).
Comparison of Methods
| Parameter | SE | SWE |
|---|---|---|
| Type of Assessment | Qualitative (relative stiffness in FOV) | Quantitative (SWS in m/s → kPa) |
| Source of Stress | Probe compression, physiological movement, ARFI | Acoustic impulse, ARFI, TE |
| Operator Dependence | Higher | Lower (Griffith, 2025) |
Diagnostic Accuracy by Organ
Breast (Berg, 2019): SWE vs strain — sensitivity 94% vs 80–100%, specificity 81–91% vs 80–95%. Quality indicators (color scale, color overlay, or number) ensure correct compression.
Thyroid (EFSUMB, 2026): There is no consensus on stiffness ranges for distinguishing benign from malignant nodules, as values differ between manufacturers. A meta-analysis (14 studies, 2,851 nodules) suggested thresholds of 26.6–85.2 kPa; 2D-SWE showed high diagnostic accuracy with average sensitivity and specificity.
Liver (WFUMB, 2024): SWE has taken an important role in the diagnosis and management of patients with chronic liver disease.
Limitations and Method Selection
Elastography is a useful adjunct to standard ultrasound but is not specific enough as a standalone method for characterizing soft tissue formations or differentiating benign from malignant masses (Griffith, 2025). In the MSK area, it is most useful for carpal tunnel syndrome, Achilles tendinopathy, and plantar fasciitis (Griffith, 2025).
Each method has advantages and disadvantages; the technique appropriate to the specific indication should be applied, and correct nomenclature should be used according to SRU and WFUMB recommendations (ACR/SRU, 2024).
Frequently asked questions
What is the fundamental difference between SE and SWE?
SE is a qualitative method comparing the relative stiffness of tissues in the field of view; SWE is quantitative, measuring shear wave speed in m/s with conversion to kPa via Young's modulus (ACR/SRU, 2024).
Which method is less operator-dependent?
SWE is less operator-dependent than strain elastography and allows for both qualitative and quantitative measurements (Griffith, 2025).
Are there universal stiffness thresholds for thyroid nodules?
No. There is no consensus, and values differ between manufacturers. A meta-analysis (14 studies, 2,851 nodules) suggested thresholds of 26.6–85.2 kPa (EFSUMB, 2026).
Can elastography be used as a standalone method?
No. It is not specific enough for standalone characterization of formations and serves as an adjunct to standard ultrasound (Griffith, 2025).
Where is elastography most useful in the MSK area?
For carpal tunnel syndrome, Achilles tendinopathy, and plantar fasciitis (Griffith, 2025).