Experimental Study Of Using Multi-Ultrasound Methods Toobserve HIFU And RF Ablation On Rabbit VX₂ Subcutaneous Transplantation Tumor

Background:Ablation therapy is an important part of the comprehensive treatment of tumors.High-intensity focused ultrasound(HIFU)is currently the only noninvasive ablation method and radiofrequency(RF)ablation is one of the most widely used minimally invasive techniques.In the process of efficacy evaluation and follow-up observation after tumor ablation,imaging methods are of great significance.Ultrasound has the advantages of real-time and low price,but conventional ultrasound can only provide gray-scale information and blood flow parameters,and can not comprehensively reflect the impact of ablation on the tumor.The use of conventional two-dimensional ultrasound,color Doppler ultrasonography,contrast-enhanced ultrasound,and ultrasound elastography to select the best ultrasound indexes for post-ablation efficacy evaluation and follow-up observation is of great significance.In this study,PET/CT and pathology were used as controls to analyze the efficacy of multi-ultrasound methods(conventional ultrasound,contrast-enhanced ultrasound and shear wave elastography)in follow-up observations of rabbit VX2 subcutaneous tumors after HIFU and RF ablation.Objective:To evaluate the feasibility of multi-ultrasound methods in the efficacy evaluation and follow-up observation of HIFU and RF ablation of rabbit VX2 subcutaneously transplanted tumors compared with PET/CT and pathology.METHODS:Rabbit VX2 subcutaneous xenograft models were established and subjected to HIFU and RF ablation.After ablation,two-dimensional ultrasound,color Doppler ultrasonography,contrast echocardiography,and shear wave elastography(SWE)were performed at different time points to observe the ablation zone acoustic changes in parametersand to screen ultrasound indicators for efficacy evaluation and follow-up observation.PET/CT were performed at the timepoint before RF and at the day the rabbits were executed.Pathology were as controls.Results:After HIFU and RF ablation,the SWE measured in the ablation area showed regularity.The measured value rose first and then decreased.After 30 days or 14 days after ablation,the SWE measured value was stable.The peak of SWE measured value appeared one day after ablation.The differences were statistically significant at(97.44±23.09)kpa and(176.31 ±9.70)kpa(p<0.05).Compared with pre-ablation,the difference was statistically significant(p<0.05).According to pathological results,the changes in ablation zone stiffness and ablation zone fibrosis were not synchronized at each time point,and changes in SWE measurements in the ablation zone may be affected by cavitation effects.In terms of residual lesions after RF ablation,the specificity of PET/CT was significantly higher than that of contrast echocardiography(p=0.03<0.05),and PET/CT was able to distinguish residual lesions and inflammatory reactions around the ablation zone.According to the pathological diagnosis cases,the residual area after RF ablation was determined by PET/CT.The difference of SWE before and after ablation,ablation zone and residual zone was analyzed.Emax and ESD in ablation zone were greater than before and after ablation(p<0.05).The Emax and ESD parameters may be more sensitive than the other SWE parameters in differentiating the tumor ablation residue.The Emax in the ablation zone were approximately(19.14±2.09)kpa,respectively.For the two parameters of Emax and in the ablation zone,the ROC curve was analyzed to determine the Emax diagnostic cut-off value of 17.50 kpa,and its Youden Index of approximately 0.90.Conclusion:After HIFU and RF ablation of rabbit VX2 subcutaneously transplanted tumors,the changes of SWE sonogram and target parameters showed some regularities.After ablation,there was different hardness in ablation zone.SWE could be used for follow-up HIFU and RF ablation of Rabbit VX2 subcutaneous tumors.In terms of efficacy evaluation after ablation,compared with PET/CT,conventional ultrasound,contrast-enhanced ultrasound,and SWE techniques do not have advantages.In the immediate assessment after ablation,contrast-enhanced ultrasound imaging clearly reflects the ablation range compared with SWE.Emax may have a reference value in the evaluation of post-ablation efficacy and follow-up,and may become a preliminary screening index before PET/CT review.