| Objective: To study the relationship between MRI findings and pathological findings before and after radiofrequency ablation of rabbit liver VX2 tumor.To study the mechanism of changes in MRI imaging signals before and after radiofrequency ablation by measuring the water content in tumor lesions,ablation zones and surrounding normal liver tissue.Methods: Among a total of 22 New Zealand white rabbits,2 were randomly selected and VX2 tumor cells were implanted in the hind leg muscle gap;when the tumor is formed,it is passed on to the next generation.In the remaining 20 rabbits,tumor cells were implanted on the left lobe of the rabbit liver by MRI-guided percutaneous transhepatic implantation.After 4 weeks,MRI was performed to confirm the tumor growth and size ? 1.5cm.Two of them were killed to confirm VX2 tumor by pathological examination.The remaining 18 tumor rabbits were randomly divided into three groups: 5 rabbits in group A,8 rabbits in group B,and 5 rabbits in group C.Rabbits in group A and group B received MRI-guided RFA on liver VX2 tumor.After the single ablation routine MRI was performed to determine the efficacy of ablation.For group A,pathologic examination of ablation zones was performed with semi-quantitative analysis to study the association between imaging findings of ablation zones 3D-vibe-T1 WI sequence and pathologic findings.For group B,samples were taken from areas of ablation zones(original tumor lesions area after RFA,ablated liver tissue area,and edema area in liver tissue)and normal liver tissue to determine the water content of each area.Experimental rabbits in the group C were immediately killed after MRI scanning,and samples from the tumor tissues and the surrounding normal liver tissues were taken out with the same method,and employed to detect their water content.The relationship between water content of each area in ablation zones and tumor lesions,and changes in MRI findings before and afterablation were analyzed.Results: 1.The rabbit liver VX2 tumor model was successfully established by MRI-guided percutaneous transhepatic implantation;pathological examination confirmed 22 tumor leisons in a total of 20 tumor rabbits.Rabbit liver VX2 tumor MRI findings: mostly round with clear boundary,tumor lesions diameter of 1.5-3.8cm with average diameter of 2.51 ± 0.62cm;low field signal in 3D-vibe-T1 WI and lower signal for the center area of larger tumor lesions;high field signal in fs-tse-T2 WI and higher signal for the center area of larger tumor lesions;high field signal in DWI(b = 800 s / mm3)and reduced corresponding ADC diagram signal due to limit.2.MRI-guided RFA was successfully performed on 14 tumor lesions in a total of 13 tumor rabbits in group A and group B.MRI findings of complete ablation: visible target in 3D-vibe-T1 WI,i.e.,original VX2 tumor lesions at the center of ablation zones still show low field signal and surroundings are high signal shadow with clear boundary between the two,The most peripheral shadow seems to have a thin layer of lower signal,but not clear boundary;in fs-tse-T2 WI,ablation zones generally show low signal change,the original tumor signal from its surrounding structures melting oven is lower,the most periphery seems to have a thin layer signal;in DWI(b = 800s/ mm3),the high signal is decreased to low signal in original tumor leisions at the center of ablation zones and surroundings are also low signal;in corresponding ADC,ablation zones overall show high signal.The semi-quantitative analysis was used to study the tumor composition of pathological specimens of ablation zones,suggesting that,in the low signal area at the center of ablation zones,most were VX2 tumor cells of coagulation necrosis,accounting for nearly 90% with fiber capsule of inflammatory edema and a small amount of vacuolar erythrocytes at the edge and no normal liver cells were observed;in peripheral high signal ring area,most were liver cells of degenerative necrosis and a large number of vacuolar erythrocytes,altogether accounting for almost 100% with a small number of inflammatory cells at the edge and no VX2 tumor cells were found.3.The determination of water content of ablation zones,tumor lesions and normalliver tissue in tumor rabbits in group B and group C and statistical analysis showed that,(1)The water content of VX2 tumor tissue was higher than that of liver tissue(T=-1.7.750,df = 4,P = 0.000 <0.05);(2)RFA caused coagulation necrosis and dehydration,resulting in water content of original tumor lesions after RFA was lower than that before RFA(T =-3.359,df = 8,P = 0.01 < 0.05);(3)Water content of each area in ablation zones and normal liver tissue: original tumor lesions after RFA >normal liver tissue area ? edema liver tissue area > ablated liver tissue area(comparisons between any two areas showed statistically significant difference with P values <0.05,except normal liver tissue area-edema liver tissue area with P = 0.334>0.05,which was not statistically significant).Therefore,in 3D-vibe-T1 WI,T1 value in original tumor lesions after RFA was the longest,showing low signal changes;besides lowest water content,ablated liver tissue area showed a large number of vacuolar erythrocytes,hemoglobin loss,and iron-containing hemolysin infiltration into cell gaps,all of which resulted in shorted T1 value,showing high signal changes;changes in T1 values of normal liver tissue area and edema liver tissue area were not obvious and in between,the signals of which were similar and between the former two.Conclusion: 1.MRI-guided rabbit liver VX2 tumor transcutaneous liver implantation is an accurate and effective modeling method.2.MRI-guided rabbit liver VX2 tumor RFA is a minimally invasive and feasible treatment.3.In MRI plain scan 3D-vibe-T1 WI sequence,ablation zone shows characterized target change,which can be used to accurately determine the immediate effect of RFA in liver tumors.4.Substantial bleeding in ablated liver tissue area after RFA and changes in water content of each tissue area that form the targets are related to its MRI signal changes to some extent. |
PDF Full Text Request