Is the reproducibility of shear wave elastography of thyroid nodules high enough for clinical use? A methodological study

Objective: To systematically assess the reproducibility of thyroid ultrasonographic shear wave elastography (SWE). Context: SWE has been suggested as a potential tool for thyroid nodule evaluation, but assessment of its reproducibility has been insufficiently addressed. Design: SWE examinations were performed prospectively by two investigators. Patients: Seventy-two patients (male/female: 19/53; mean age: 53 ± 14 years; malignant/benign 17/55) undergoing thyroid surgery were enrolled in the study. Measurements: Repeated and blinded measurements of elasticity index (EI) in predefined regions of interest (ROI) were collected. The inter- and intrarater agreement, along with the day-to-day agreement, was evaluated in terms of the 95% limits of agreement (LOA). Results are presented as a ratio, by which 1·0 indicates perfect agreement. Results: The interrater, intrarater and day-to-day LOA showed ratios between repeated measurements of 1·7–3·6, 1·8–3·7 and 2·2–2·9, respectively. These values reflect a low to moderate degree of agreement for all EI outcomes. The interrater LOA was higher for malignant nodules compared with benign nodules for six of seven EI outcomes (P < 0·001–0·03). The proportion of agreement calculated from the optimum cutoff point for differentiating malignant from benign nodules was 63–88% for the investigated EI outcomes. Conclusions: In this methodological study, EI measured by thyroid SWE seems suboptimal for clinical use, due to a low inter- and intrarater agreement. That EI varies from day to day furthermore jeopardizes the validity of the method. Although the proportion of agreement was acceptable for some EI parameters, it is questionable whether EI assessments can reliably differentiate malignant from benign nodules in the individual patient.