Visualization of tissue alterations in thyroid nodules after microwave ablation: sonographic versus scintigraphic imaging.

Objective: The aim of this study was to elucidate the potential of B-mode sonography, colour-coded Doppler sonography and scintigraphic imaging as diagnostic methods for the evaluation of treatment success and follow-up of thyroid nodules after microwave ablation.

Materials And Methods: Thirty-six thyroid nodules in 33 patients were subjected to microwave ablation and were evaluated by means of B-mode sonography, colour-coded Doppler sonography and scintigraphic imaging before and after ablation. B-mode sonography results were characterized by echogenicity that was assigned ultrasound scores (US). Hypoechoic nodules were referred to as US1, isoechoic as US2 and hyperechoic nodules as US3. Colour-coded Doppler sonography was evaluated by a scoring system reflecting the blood flow of ablated nodules. A Doppler score (DS) of 1 was assigned for nodules without blood flow, DS2 for those with an absence of intranodular but presence of perinodular blood flow and DS3 for nodules with intranodular and perinodular flow. Scintigraphic imaging was performed using technetium-99m pertechnetate (99mTc-pertechnetate) for pretherapeutic and post-therapeutic imaging of indifferent nodules and 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) as the tracer for cold nodules.

Results: B-mode sonography reflected decreased echogenicity and US [median decrease by Δ=1±0.6 (P<0.01)] after ablation. Colour-coded Doppler sonography showed declined blood flow; median reduction of DS was Δ=1±0.7 (P<0.01). In scintigraphic imaging, tracer uptake reduced by a median 42.5±27.8% (P<0.01). 99mTc-pertechnetate scans recorded tracer uptake reduction by 32.3±17.8%, and 99mTc-MIBI scans showed uptake reduction in ablated regions by 56.1±29.7%.

Conclusion: 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.