Diagnostic accuracy of elastography and scintigraphic imaging after thermal microwave ablation of thyroid nodules.

PURPOSE The aim of this study is to evaluate structural alterations of thyroid tissue after microwave ablation using elastography and scintigraphic imaging to investigate the applicability of these diagnostic methods for follow-up.  MATERIALS AND METHODS 35 patients with 39 thyroid nodules were evaluated using elastography and scintigraphic imaging before and after ultrasound-guided microwave ablation. Elastography was analyzed according to color-coded output and results were classified using a fourfold elasticity score (ES). Nodules color-coded blue were classified ES1 for high elasticity through ES2 and ES3 for lower elasticity, and nodules with very low elasticity were color-coded red and classified as ES4. (99m)Tc-pertechnetate served as a tracer for scintigraphic imaging of hot and indifferent nodules and (99m)Tc-MIBI for cold nodules. RESULTS Before microwave ablation, elastography detected a median elasticity score of ES 2 ± 0.7, and after ablation the median score was ES 3 ± 0.6. Overall, the median score increased by 1ES ± 0.6 (p < 0.01). Scintigraphic imaging detected a median reduction of tracer uptake in ablated tissue of 38.7 %± 27.5(p < 0.01). (99m)Tc-pertechnetate scans showed a median decrease of tracer uptake of 26.3 %± 16.3 and (99m)Tc-MIBI scans detected uptake reduction of 54.7 %± 29.2. CONCLUSION Scintigraphic imaging using (99m)Tc-pertechnetate and (99m)Tc-MIBI provides quantifiable results and is promising as a diagnostic follow-up after microwave ablation. Strain elastography detects decreasing tissue elasticity, but accuracy is limited by the necessary reduction of color-coded output to elasticity scores.