Thyroid Elastography: Additional Value in Nodule Assessment
The Role of Elastography in Multiparametric Assessment
Elastography is considered an additional method in the multiparametric ultrasound assessment of thyroid nodules (EFSUMB Guidelines on Multiparametric Ultrasound Thyroid Nodule Evaluation, Cantisani et al.). It does not replace grayscale assessment and TI-RADS stratification but adds information about tissue stiffness.
Correct Methodological Sequence
According to the accepted methodology, the sequence of actions is as follows: first B-mode, then elastogram.
Rationale:
- Formation boundaries are determined by grayscale imaging — it has higher spatial resolution and real anatomical contours.
- Elastogram — a functional stiffness map in the same plane; it is superimposed on B-mode or displayed alongside. It assesses the stiffness distribution within the already identified formation and around it.
Calculation of Strain Ratio (Compression Elastography)
| ROI | Location |
|---|---|
| Nodule ROI | In the zone of maximum stiffness or covers the entire formation (according to the device protocol) |
| Reference ROI | In the surrounding tissue at a comparable depth — for thyroid, parenchyma nearby (for breast, usually adipose tissue) |
Why Not to Primarily Rely on Elastogram
Compression elastography depends on pressure, depth, and preload, and contains many artifacts. A stiff halo may extend beyond the real boundaries of the nodule, while a soft center (necrosis, colloid) may "hide" part of the formation. Therefore, boundaries are always determined by B-mode, and stiffness by the color map.
Final algorithm: B-mode → identification and outlining of the formation → elastogram for stiffness assessment.
Shear Wave Elastography (SWE)
The literature included in the EFSUMB guidelines discusses the value of SWE and ARFI elastography for the differential diagnosis of thyroid nodules, including in the absence of highly suspicious features on conventional ultrasound, as well as for preoperative risk stratification of follicular formations [specify specific thresholds — not provided in the excerpts].
Specific numerical stiffness thresholds (kPa / m/s) for differentiating benign and malignant thyroid nodules are not specified in the provided excerpts — [specify].
Frequently asked questions
What should be outlined first — the formation on B-mode or on the elastogram?
First B-mode: it has higher spatial resolution and real contours. The elastogram is assessed after identifying the formation — as a functional stiffness map in the same plane.
Where to place the reference ROI for strain ratio in the thyroid?
In the surrounding parenchyma near the nodule at a comparable depth. The nodule ROI is placed in the zone of maximum stiffness or covers the entire nodule according to the device protocol.
Why can't the boundaries of the nodule be determined by the elastogram?
Compression elastography depends on pressure, depth, and preload, and is rich in artifacts. A stiff halo may extend beyond the nodule boundaries, while a soft center (necrosis, colloid) may hide part of the formation.
What elastography methods are used for thyroid nodules?
Compression elastography with strain ratio calculation and shear wave elastography (SWE), as well as ARFI. They are part of the multiparametric EFSUMB approach as an addition to B-mode and TI-RADS.