Added Value of Ultrasound Elasatography in Characterization of Thyroid Nodules

US elastography has been used to detect the nature of thyroid nodules, by measuring the tissue stiffness non invasively. It depends on tissue deformation strain that is caused by external compression.it is complementary to gray scale findings particularly in nodules with indeterminate US findings, also US elastography could be used to guide the follow up of leisons diagnosed as benign at ( FNA) fine needle aspiration .

There are two main thyroid elastography methods in clinical practice: strain elastography (SE) and shear-wave elastography (SWE) .

Elastography methods can be classified into different variants based on the excitation method (external force, internal force, and acoustic radiation force [ARF]), and how stiffness is expressed . (A) strain elastography . SE reqires mechanical stress, which results in axial displacement of the tissue Tissue deformation from the stress is measured and visualized on a screen. The main limitations of SE are operator dependence for the angle, strength, and duration of compression.

(B) shear wave elastography . The acoustic pulses from the probe stimulate the target tissue, creating a shear wave (SW) traveling perpendicular to the conventional US waves. SWs are the transverse components of particle displacement that are rapidly attenuated by the tissue (1- 10 m/sec). This transverse component is tracked and measured as a numerical value corresponding to the shear-wave speed (SWS).This speed is closely related to the Young modulus formula, in which tissue elasticity can be assessed from the SW propagation.

US elastography is completely painless for the patient, and only requires a few extra minutes, with no separate patient preparation. US elastography has the potential to distinguish benign from malignant TNs, offering non-invasive complementary information to conventional US.