Morphologic and Functional Changes in Nontumorous Liver Tissue After Radiofrequency Ablation in an In Vivo Model: Comparison of ¹⁸F-FDG PET/CT, MRI, Ultrasound, and CT

¹ Department of Diagnostic and Interventional Radiology and Neuroradiology, University Duisburg–Essen, Essen, Germany
² Department of Nuclear Medicine, University Duisburg–Essen, Essen, Germany
³ Department of Pathology, University Cologne, Cologne, Germany

^* To whom correspondence should be addressed. E-mail: florian.vogt{at}uni-essen.de.

	Abstract

Rimlike contrast enhancement on morphologic imaging and increased tracer uptake on ¹⁸F-FDG PET in the periphery of the necrosis can hamper differentiation of residual tumor from regenerative tissue after radiofrequency ablation of liver lesions. This study used MRI, CT, ultrasound, and ¹⁸F-FDG PET/CT to assess the typical appearance of lesions in nontumorous animal liver tissue after radiofrequency ablation. Methods: Lesions were created by radiofrequency ablation of normal liver parenchyma in 21 minipigs. Follow-up was performed by 3 contrast-enhanced morphologic modalities—MRI, CT, and ultrasound—and by ¹⁸F-FDG PET/CT immediately, 3 and 10 d, and 1, 2, 3, and 6 mo after radiofrequency ablation. Images were evaluated qualitatively for areas of increased enhancement and regions of elevated tracer uptake. Furthermore, all images were assessed quantitatively by determination of ratios comparing enhancement/tracer uptake in the periphery of the necrosis with enhancement/tracer uptake in normal liver parenchyma. Imaging findings were compared with histopathology findings. Results: Immediately after radiofrequency ablation, no increase in ¹⁸F-FDG uptake was visible, whereas elevated enhancement was noticed in the periphery of the necrosis on all morphologic imaging procedures. At further follow-up, an area of rimlike increase in ¹⁸F-FDG uptake surrounding the necrosis was detected on PET/CT. The rimlike pattern of increased enhancement in the arterial phase was present for all liver lesions on CT, MRI, and ultrasound, especially between day 3 and month 1 after the radiofrequency ablation. Both elevated glucose metabolism and enhancement persisted for 6 mo postinterventionally. Histologic examination showed a hemorrhagic border converting into a regeneration capsule. Conclusion: If performed immediately after radiofrequency ablation, ¹⁸F-FDG PET/CT probably has benefits over those of morphologic imaging procedures when assessing liver tissue for residual tumor. Later follow-up may be hampered by visualization of peripheral hyperperfusion and tissue regeneration. Further studies on a patient population are essential.

Key Words: minimally invasive technique, tissue necrosis, periablational region, peripheral enhancement, tissue response