Ultrasound elastography for evaluation of cervical lymph nodes

Abstract

Ultrasound (US) elastography has been introduced as a noninvasive imaging technique for evaluating cervical lymph nodes. US elastography techniques include strain elastography and shear wave-based elastography. The application of this technique is based on the fact that stiff tissues tend to deform less and show less strain than compliant tissues when the same force is applied. In general, metastatic lymph nodes demonstrate higher stiffness than benign lymph nodes. Overall, preliminary studies suggest that US elastography may be useful in differentiating benign and malignant cervical lymph nodes, thereby informing decisions to perform a biopsy and facilitating follow-up. For US elastography to be accepted into clinical practice, however, its techniques, associated diagnostic criteria, and reliability need to be further refined.

Keywords: Elasticity imaging techniques; Lymph nodes; Neck; Ultrasonography.

Fig. 1.. Schematic representation of ultrasound elastography.

A. Strain elastography measures tissue displacement that occurs along the axis of the applied force. B. Shear wave-based elastography measures the shear waves that are generated by the tangential sliding of the tissue particles, which travel perpendicularly to the direction of the applied force.

Fig. 2.. Elastographic scale (ES) used to assess lymph nodes.

ES 1 (soft), predominantly red and green areas with <10% of the area colored as blue; ES 2 (moderately soft), predominantly red with blue areas comprising between 10%-50% of the area; ES 3 (moderately stiff), predominantly blue and green areas comprising 50%-90% of the total area; ES 4 (stiff), predominantly blue areas comprising >90% of the total area.

Fig. 3.. Strain ratio.

In strain elastography with a corresponding gray-scale sonogram of a metastatic lymph node, the region of interest is centered on the lymph node and normal muscle. The strain ratio is 3.64, which indicates a lesion that is stiffer than normal muscle.

Fig. 4.. Sonogram of a reactive hyperplastic lymph node showing acoustic radiation force impulse (ARFI) measurements in the selected region.

The region of interest for the ARFI measurement is the square box, and the mean ARFI velocity for the region of interest is 1.14 m/sec.

Fig. 5.. Sonogram of a metastatic lymph node showing supersonic shear imaging measurements in a selected region.

The region of interest for supersonic shear imaging measurements is the circle, and the mean elastic modulus is 32.30 kPa.

Fig. 6.. Nonaxial compression that degraded the accuracy of the software’s correlation algorithm.

A, B. Nonaxial compression degrades the elastographic scale (ellipses) in the supraclavicular area (A), which is due to the varying mobility of the different structures in the neck, which can slide nonaxially under compression (B).

Fig. 7.. Lesions for which elastography has limited value.

A, B. The cystic portion of the lymph node (A) and a calcification (B) lack an elastographic scale (arrows).