Impact of Image Orientation on Measurements of Thyroid Nodule Stiffness Using Shear Wave Elastography

Objectives-To assess the effect of orientation on the stiffness measurement by shear wave elastography (SWE) within a thyroid nodule. Methods-Forty-five patients with 50 thyroid nodules were enrolled in this study. After a short sonographic examination, SWE images were acquired in transverse and longitudinal orientations. Multiple elastograms of each nodule were obtained in both orientations. Mean and maximum stiffness values were recorded from each region of interest. The overall mean and maximum stiffness values of each nodule were calculated for both orientations separately. The concordance correlation coefficient was used to assess overall agreement between measurements. A receiver operating characteristic curve analysis was conducted to assess diagnostic performance for benign versus malignant nodules. Results-The 45 patients included 6 men and 39 women (mean age, 53 years; range, 23-84 years). The mean stiffness values +/- SD were 19.1 +/- 18.4 and 20.9 +/- 21.5 kPa for transverse and longitudinal measurements, respectively, with a small overall bias between the orientations (1.8 kPa; P=.09). Overall agreement was good (concordance correlation coefficient, 0.93) although moderated somewhat after the stiffness values were log transformed to reduce skewness (concordance correlation coefficient, 0.76). Of the 50 nodules, 6 were classified as malignant. The area under the curve based on the mean stiffness value from longitudinal images tended to be better than for transverse images, but the difference was not statistically significant (0.93 versus 0.83; P =.17). Conclusions-Our study has shown that good diagnostic performance can be achieved by using SWE in longitudinal and transverse orientations. Moderate to good agreement in mean and maximum stiffness values for both orientations was observed, with only a small bias. Diagnostic performance for benign and malignant nodules was similar. The similar performance of both orientations gives flexibility in imaging patients with anatomic or physical limitations.