!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 Tcpertechnetate 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.

B-mode sonography and colour-coded Doppler sonography are easily applicable, providing real-time imaging control for microwave ablation. However, they are limited in accuracy and susceptible to artefacts. Scintigraphic imaging delivers quantifiable, operator-independent results and is promising in the evaluation of treatment success and follow-up.