Microwave ablation (MWA) is a type of minimally invasive cancer therapy that uses heat to induce necrosis in solid tumours. Inter-and post-ablational size changes can influence the accuracy of control imaging, posing a risk of incomplete ablation. The present study aims to explore post-ablation 3D size dynamics in vivo using computed tomography (ct). ten MWA datasets obtained in nine healthy pigs were used. Lesions were subdivided along the z-axis with an additional planar subdivision into eight subsections. The volume of the subsections was analysed over different time points, subsequently colour-coded and three-dimensionally visualized. A locally weighted polynomial regression model (LoeSS) was applied to describe overall size changes, and Student's t-tests were used to assess statistical significance of size changes. The 3D analysis showed heterogeneous volume changes with multiple small changes at the lesion margins over all time points. the changes were pronounced at the upper and lower lesion edges and characterized by initially eccentric, opposite swelling, followed by shrinkage. In the middle parts of the lesion, we observed less dimensional variations over the different time points. LOESS revealed a hyperbolic pattern for the volumetric changes with an initially significant volume increase of 11.6% (111.6% of the original volume) over the first 32 minutes, followed by a continuous decrease to 96% of the original volume (p < 0.05). Microwave ablation (MWA) is a thermoablative procedure for the minimally invasive therapy of solid tumours, primarily in the lungs, kidneys and liver. It uses electromagnetic waves to induce local coagulation necrosis through heat 1-3. During the ablation procedure, high local temperatures of up to 120 °C can be achieved in the target tissue, not only causing protein denaturation but also for example evaporation of the water contained in the tissue and resulting in changes of dielectric and thermal properties as well as structural tissue changes 4-6. Overall, these structural changes can lead to dynamic alterations in lesion morphology and lesion size in the post-ablation period. Tissue shrinkage, primarily caused by dehydration, but also by tissue evaporation and carbonization, is an important change in the ablation area and ought to be considered in post-interventional imaging as it can cause a decrease in lesion volume of up to 30% and could therefore be of clinical relevance 7-9. Contrast-enhanced computed tomography (CECT) is often performed after MWA to determine the size and safety margin of the ablation area in order to ensure complete tumour ablation 10-13. CECT has been shown to allow identification of the central necrotic area of the ablated tissue, which displays little to no contrast medium uptake and thus appears hypodense compared to normal liver tissue (NLT) 14. Recent studies using CECT ex vivo or in vivo demonstrated the shrinkage of ablation zones in the first hours after MWA, but so far, no precise analysis of the dynamic size behaviour has been carried out ...
