| Objective:The changes of MRI(magnetic resonance imaging)signal was observed after the microwave ablation of rabbit renal VX2 tumor under MRI guidance.The comparative analysis was conducted between the pathological manifestations after ablation and MRI signal to explore the feasibility of microwave ablation of renal tumor under MRI guidance and the MRI-pathology correlation of ablation of renal tumor.Methods:Part ?:Preparation of CT-guided rabbit renal VX2 tumor model.The frozen VX2 tumor cell line was thawed and revived,and then implanted into the thigh muscle of New Zealand male white rabbit to form tumors.After 2-3 weeks,the VX2tumor on the lateral hind leg of the tumor-bearing rabbit was taken out under sterile conditions.The fish-flesh like tissue with vigorous growth was selected and cut into tissue blocks of about 1mm~3 with ophthalmic scissors for later usage.Twelve experimental rabbits were implanted with tumor by CT-guided percutaneous renal puncture.In order to reduce the risk of infection and death after puncture,only one side kidney was implanted with tumor.The experimental rabbits were fixed on the CT scan bed after skin preparation and anesthesia,and the localization scan was performed to determine the puncture path and depth.After conventional disinfection of the skin and draping was prepared,the VX2 tumor tissue block was implanted into the renal parenchyma of one side of the experimental rabbits with gradually insertion using 17G puncture needle under the guidance of CT.After 2-3 weeks,MRI scan was performed to confirm tumor growth with a diameter of more than or equal to 1.0 cm.MRI manifestations of tumor lesions were observed.Two tumor-bearing rabbits were randomly sacrificed for pathological confirmation.Part II:MRI-guided Microwave ablation of rabbit renal VX2 tumor and MRI-pathology correlation.After 8 renal tumor-bearing experimental rabbit skins preparation and the general anesthesia were prepared,the rabbits were fixed in MRI scans bed to receive MRI scan using surface localization of vitamin E pills.After puncture path and depth is determined,we cut 2mm small incision in the skin with surgical blade and punctured the lesions using 15 G MRI compatible microwave antenna gradually.After confirm the microwave antenna punctured in the centre of the lesion by scanning again,then cables and water circulation were connected and set microwave power output as 50W to 60W,continuous treatment 3-5 min.MRI scan was performed immediately after ablation to observe the changes of MRI signal in ablation lesions.If the immediate efficacy evaluation of ablation was satisfactory,postoperative complications were observed after needle removed through MRI scanning immediately.If the immediate efficacy evaluation of ablation was not satisfactory,ablation was performed again.After MRI scanning,the experimental rabbits were sacrificed and their kidneys were taken out and examined by gross pathology and histopathology.The length and width of the tumor and the coagulative necrosis area were measured.The long and wide diameters of the tumor lesion on the fs-tse-T2WI sequence before ablation,the central low signal area and the surrounding high signal area on the 3D-Vibe-T1WI sequence after ablation,and the low signal area on the fs-tse-T2WI sequence after ablation were measured on MRI images.The long and wide diameters of the low signal region of the tumor lesion on the fs-tse-T2WI sequence before ablation,the central low signal region on the3D-Vibe-T1WI sequence after ablation,and the coagulative necrosis region of the tumor on the gross specimen were pairwise compared.And the long and wide diameters of the coagulative necrosis area of the ablation lesion,the high signal area around the tumor lesion in the 3D-Vibe-T1WI sequence,and the low signal area in the fs-T2WI sequence were pairwise compared.Gross pathological tissue were obtained,fixed,paraffin embedded and sections were made for HE staining.The pathological changes of rabbit kidney VX2 tumor after ablation were observed under microscope.Results:Part ?:11 of the 12 experimental rabbits were successfully implanted with VX2 tumor in the kidney and a total of 11 tumor lesions were formed.The tumor formation rate was 91.7%(11/12).The average length diameter of tumor was 1.65±1.06cm(1.12-5.00 cm)and the average width diameter of tumor was 1.40±0.99 cm(0.80-4.50 cm).Among the 11 tumor-bearing experimental rabbits,3 lesions were found in the left kidney and 8 lesions were found in the right kidney.Two lesions of the left kidney were located in the upper pole and 1 lesion was located in the lower pole of the left kidney.Three lesions of the right kidney were located in the upper pole and 4lesions was located in the lower pole of the right kidney.The diameter of the remaining one lesion of the right kidney was 5.0 cm and infringed the renal tissues and its surrounding.Considering large tumor growth excessively and invasion,this lesion was excluded the experimental group and no microwave ablation was performed.In the process of puncture implantation,there was no subcapsular hematoma,perinenal hematoma or other complications in all the experimental rabbits except a small amount of perinenal hemorrhage in one experimental rabbit.Part ?:All the 8 tumor-bearing rabbits were successfully treated with MWA for VX2 tumor of rabbit kidney under the guidance of MRI.The average operating time was 63.8±11.2 min,the average ablation power was 50.0±4.3W and the average ablation time was 4.4±0.6 min.No immediate complications were observed in the 8 experimental rabbits after ablation.Immediate MRI manifestations of rabbit renal VX2 tumor after MWA:"target sign"on the3D-Vibe-T1WI sequence,low signal representing primary tumor at the central of the ablation area,and the primary tumor surrounded by peripheral high signal area.The signal of the primary tumor in the fs-tse-T2WI sequence was lower than that before ablation.The ablation lesion showed low signal and completely covered the lesion area.The signal of ablation area on DWI showed high signal.The signal of ablation area on ADC showed low signal.Post-operative gross pathology showed that there was black charring needle duct in the ablation lesion,yellowish-white coagulative necrosis was observed in the center of the original tumor tissue,grey-yellow coagulative necrosis area around the tumor,and dark red banding hyperemia and edema area around the ablation lesion.Under the microscope of HE staining for rabbit renal VX2 tumors,the ablation area was divided into tumor coagulation necrosis area,normal renal parenchyma coagulation necrosis area and hyperemia edema area from the inside to the outside.The appearance of tumor coagulation necrosis area was that the nuclear structure of tumor was completely disappeared and only the cell contour was left.The coagulation necrosis area of normal renal parenchyma was characterized by exudation of powdery protein,dilatation of renal tubules,and massive coagulation necrosis of renal parenchyma.The peripheral hyperemia and edema area showed diffuse hemorrhage and a small amount of inflammatory cell infiltration.The fs-tse-T2WI lesion before MWA,the central low-signal area of 3D-vibe-T1WI after MWA and the tumor coagulation necrosis area showed no statistical difference in terms of length and width(P>0.05).After MWA,the high signal area around the lesion on 3D-vibe-T1WI,the low signal area on the lesion on fs-tse-T2WI and the gross pathological coagulation necrosis area showed not statistically difference(P>0.05)by pairwise comparisons.Conclusion:1.MRI-guided MWA of the treatment of rabbit renal VX2 tumor is a feasible,effective and minimally invasive intervention method.2.MRI signal changes of rabbit renal VX2 tumor after MWA have certain characteristics,which are strongly correlated with pathological changes.MRI is an effective method for immediate efficacy evaluation of renal tumor after MWA. |
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