Comparison of strain elastography, point shear wave elastography using acoustic radiation force impulse imaging and 2D-shear wave elastography for the differentiation of thyroid nodules

Abstract

Purpose: The aim of the study was to compare three different elastography methods, namely Strain Elastography (SE), Point Shear-Wave Elastography (pSWE) using Acoustic Radiation Force Impulse (ARFI)-Imaging and 2D-Shear Wave Elastography (2D-SWE), in the same study population for the differentiation of thyroid nodules.

Materials and methods: All patients received a conventional ultrasound scan, SE and 2D-SWE, and all patients except for two received ARFI-Imaging. Cytology/histology of thyroid nodules was used as a reference method. SE measures the relative stiffness within the region of interest (ROI) using the surrounding tissue as reference tissue. ARFI mechanically excites the tissue at the ROI using acoustic pulses to generate localized tissue displacements. 2D-SWE measures tissue elasticity using the velocity of many shear waves as they propagate through the tissue.

Results: 84 nodules (73 benign and 11 malignant) in 62 patients were analyzed. Sensitivity, specificity and NPV of SE were 73%, 70% and 94%, respectively. Sensitivity, specificity and NPV of ARFI and 2D-SWE were 90%, 79%, 98% and 73%, 67%, 94% respectively, using a cut-off value of 1.98m/s for ARFI and 2.65m/s (21.07kPa) for 2D-SWE. The AUROC (Area under the Receiver Operating Characteristic) of SE, ARFI and 2D-SWE for the diagnosis of malignant thyroid nodules were 52%, 86% and 71%, respectively. A significant difference in AUROC was found between SE and ARFI (p = 0.008), while no significant difference was found between ARFI and SWE (86% vs. 71%, p = 0.31), or SWE and SE (71% vs. 52%, p = 0.26).

Conclusion: pSWE using ARFI and 2D-SWE showed comparable results for the differentiation of thyroid nodules. ARFI was superior to elastography using SE.

Fig 1. SE of a thyroid nodule in the right thyroid lobe.

Histology revealed papillary carcinoma.

Fig 2. Acoustic Radiation Force Impulse Imaging (S2000, 9L4 probe at 9MHz) with the ROI placed within a hypoechoic thyroid nodule in the left thyroid lobe measuring a velocity of 0.96 m/s.

Histology revealed benign nodule.

Fig 3. 2D-SWE with the ROI placed within a thyroid nodule in the right thyroid lobe measuring a velocity of 3.7 m/s.

Histology revealed papillary carcinoma.

Fig 4. Number of nodules that underwent FNAB and/or surgery, number of benign and malignant thyroid nodules and types of thyroid cancer.

Fig 5. Comparison of ROC-Curves for SE, ARFI and 2D-SWE.