Findings Of Radiofrequency Ablation In Normal Dog Liver: Initial Study Of CT, ¹⁸F-FDG PET/CT And Histopathology

ObjectiveRadiofrequency ablation(RFA) is a minimally invasive technique for treatment of malignant hepatic tumor with less damage and more secure.But the rate of tumor residual and recurrence after operation is relatively high.To eliminate the tumor completely,1 cm spread of normal liver tissue will be ablated along with the tumor liver tissue('Security Margin').Inflammation is very likely to occur due to the lesion.And since inflammation will influence the assessment of tumor residual during imaging examination,an imaging study of normal liver RFA lesion is necessary.This thesis is to evaluate time-related histopathological changes of the normal liver lesion in dogs after radiofrequency ablation(RFA) by CT and ¹⁸F-FDG PET/CT. And thus provide diagnosis value for assessment of tumor residual.Methods and Material15 dogs were divided into 5 groups randomly(3/group) and performed CT, ¹⁸F-FDG PET/CT scan respectively at immediately,1,2,4,8 weeks after RFA procedure.Before the intervention and the subsequent imaging procedures,all animals were kept fasting for a minimum of 12 h.Blood glucose was measured before the intervention and before all follow-up imaging examinations.Radiofrequency ablation was performed twice in each dog liver separately under CT guidance with 2 cm deployment of the electrodes.And 30 ablative necrosis were obtained in total.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.Histopathological examination was performed after all dogs were killed.Correlation of lesion size between the appearance in CT,PET/CT and histopathological examination including enhancing rim,and pathologic measurements were then analyzed using the Pearson's correlation coefficient,which was used to describe the degree of correlation between all possible two-variable comparisons.ResultsRFA operation was successfully performed in 15 dogs with no complication or death occurred.Immediately after RFA procedure,no increase in ¹⁸F-FDG uptake was visible,r_p/p is 1.01±0.05,whereas elevated enhancement was noticed in the periphery of the necrosis on CT image with r_p/p of 1.34±0.21.1～4 weeks after RFA,an area of rimlike increase in ¹⁸F-FDG uptake surrounding the necrosis was detected on PET/CT and at the end of first week,r_p/p reached its peak value of 1.19±0.09,then slowly dropped.The rimlike pattern of increased enhancement in the arterial phase was present for all liver lesions on CT,especially between 1-2 weeks after the radiofrequency ablation.r_p/p value also dropped.8 weeks after RFA procedure,no area of rimlike enhancement/tracer uptake was visible and corresponded r_p/p value was down to 1.02±0.09,1.03±0.03.Histopathological examination showed hyperemia and inflammatory cell infiltration converting into a regeneration capsule.Pearson's correlation showed both CT and PET/CT are good indicators for ablative necrosis size(both long- and short axes measurements) with strongly related rs value of 0.94, 0.93 and 0.80,0.78.Compared with PET/CT,CT showed a better correlation to histopathological samples.ConclusionCT and ¹⁸F-FDG PET/CT imaging can well correlate the histopathological changes by RFA in the liver.The design of 'immediate group' after operation could eliminate inflammation influence and thus be well adapted to evaluate early RFA curative effect.CT and PET/CT examination of '8 w group' could avoid physiology influence of normal liver and thus be no hamper to evaluation of RFA curative effect.