Experimental Study On The Effects Of Microwave Ablation On Thermal Damage And Thermal Field Distribution Of Cystic Lesions And Solid Cystic Tumors

Objective To establish the bladder tumor model of VX2 carcinoma in rabbits by simulating the mechanism of development of orthotopic bladder cancer,and study its biological features and imaging findings.Methods VX2 tumor tissue were implanted into the total of 25 healthy New Zealand White rabbit bladders by coaxial puncture embedded method,and evaluated tumor seeding and growth by CT scanning and pathological examination at 2、3、4 weeks after surgery,also observed the abdominal lymph nodes and liver and lung metastasis.Results Establishment of rabbit model bearing VX2 bladder tumor were successful in 22 rabbits(88.0%,22/25).At 2、3、4 weeks after surgery,the mean long diameter of the tumors was 1.38±0.20cm、2.30±0.08cm、3.22±0.24cm respectively,and there was significant difference(P<0.01)of tumor volume in the second and third week.The tumors demonstrated itself as irregular thickening bladder wall or local mass accompanied with heterogeneous density on plain CT scans,homogeneous enhancement(2 weeks)or ring enhancement(3,4 weeks)on early arterial phase images and filling defect in the bladders on delayed phase images.Histopathology of VX2 revealed hypervascular poorly differentiated squamous-cell carcinoma.Necrosis was found in the center of all bladder tumors at 3 week after surgery,3～4 weeks showed extensive abdominal lymph nodes,liver and bilateral lungs metastasis.Conclusions An experiment model of transplantable VX2 carcinoma was established in rabbit bladders,and reflected the development and progression of human bladder cancer approximately.It was an ideal model fitting CT study and fundamental research.Objective To develop the in vitro-normal rabbit urinary bladder and VX2 bladder tumor by simulating the mechanism of cystic lesion and cystic-solid tumor,and study establishment and imaging findings of cystic lesion and cystic-solid tumor model.Methods In vitro-normal urinary bladder and VX2 bladder tumor model were prepared,and immobilized by agarose gel,and established the cystic lesion and cystic-solid tumor model.On the basis of cystic/cystic-solid model and rabbit bladder diameter divided into 4 groups,Group I cystic lesion(3.0cm),Group II cystic-solid tumor(3.0cm),Group III cystic lesion(5.0cm),Group IV cystic-solid tumor(5.0cm),12 rabbits per group.CT imaging evaluation respectively,and statistical analysis.Results A total of 48 rabbits were included in 24 normal urinary bladders and 24 VX2 bladder tumors.It is successful for 48 cases surgical operation to use intravenous anesthesia,22.012.7min per case.A total of in intro-bladders removed were 45 cases(93.75%),including 22 cases(45.83%)normal urinary bladders and 23 cases(47.92%)VX2 bladder tumors.3 cases(6.25%)were due to injury of bladder wall and VX2 tumor abdominal wall metastasis,unable to remove the complete rabbit bladder.In this experiment,agarose gel(4g/200ml)was selected for immobilization preparation,the ideal temperature of agarose solution was range from 45°C to 40°C,45.0±5.2min per case.The agarose gel fixation strength and transmittance were suitable for model production.The cystic and cystic-solid tumor model demonstrated itself as regular bladder wall or local mass accompanied with heterogeneous density on plain CT scans.The VX2 bladder tumor demonstrated itself as filling defect in the bladder after contrast agent administration,VX2 tumor mean diameter was 1.65±0.51cm.Conclusion An experiment model of cystic lesion and cystic-solid tumor was established successfully in stable physical and chemical properties,the preparation was safe,simple and reproducible.It was an ideal model fitting CT evaluation and fundamental research.Objective To investigate the feasibility and effectiveness of microwave thermal ablation for cystic lesion and cystic-solid tumor,and discuss the relations between microwave power,duration and temperature variation.Methods 63 cases of normal experimental rabbits and 63 cases of VX2 bladder tumor rabbits were treated with intravenous anesthesia,routinely sterilising,draping,and celiotomy incision.In vitro-normal urinary bladder and VX2 bladder tumor model were prepared,and immobilized by agarose gel,and established the cystic lesion and cystic-solid tumor model.On the basis of microwave ablation parameters and rabbit bladder diameter divided into 6 groups:Group I and VI were control groups without ablation;Group Ⅱ,Ⅲ,Ⅳ,Ⅵ were experimental groups with ablation in power condition(60W)and temperature condition(70°C),duration of ablation was 4min,6min,8min,10min,12min.After microwave ablation,the bladders and VX2 tumor were removed from the agarose gel,and performed anatomical observation and pathological examination,and statistical analysis.Results A total of 62 cases cystic lesion models and 62 cases cystic-solid tumor models were successfully established,one case of cystic lesion model due to bladder wall injury leading to fluid leakage and one case abdominal metastasis of VX2 tumor resulted in failure of modeling.Group I and VI were the control group without ablation,under optical microscope,the epithelial cells of the normal bladder wall were well formed and the internal structure of the cells was intact.Group II,III,IV and V were cystic lesion and cystic-solid tumor with ablation,ablation power and the temperature of bladder wall were positively correlated.The temperature of cystic lesion model was on effective ablation temperature(70° C),under optical microscope,the bladder mucosa epithelial cell degeneration and necrosis.The histocyte structure of bladder wall was completely disappeared,VX2 tumor cell showed coagulation necrosis,nuclear condensation and nuclear condensation,nuclear fragmentation.Conclusions A tissue-mimicking phantom for cystic lesion and cystic-solid tumor in in vitro-normal rabbit urinary bladder and VX2 bladder tumor was fitted to the thermal ablationas,and the microwave thermal ablation for cystic lesion and cystic-solid tumor was feasible and effective.Objective To investage thermal field distribution and uniformity of microwave ablation in homogeneous liquid media,and discuss the mode of thermal energy transfer.Methods A total of 64 cases New Zealand normal rabbits were simulating to in vivo/in vitro cystic lesion model,on the basis of rabbit bladder diameter(3cm,5cm)and in vivo/in vitro conditions divided into experimental group(40W,60W,80W)and control group.The cystic lesion model(left side,right side,top side,bottom side,cystic liquid)was measuring real-time temperature,and using infrared thermal imaging instrument to dynamically monitor the thermal field distribution.The macroscopical and histological changes of cystic lesion model were evaluated,and statistical analysis.Results A total of 60 cases in vivo/in vitro cystic lesion models were preformed microwave ablation,every case had 5 temperature point,and 4 cases without microwave ablation in the control group.There was a positive correlation between the temperature gradient of cystic lesion model(wall and liquid)and microwave ablation power.The temperature of cystic left side wall was similar to right side wall(P>0.05),and below average of cystic top wall and liquid(P>0.05),and obviously higher than cystic bottom wall(P<0.01),all temperature values were balanced finally.The microwave thermal field was regional distribution in in vivo/in vitro cystic lesion model,the region and range of thermal field was associated with ablation duration.The temperature of cystic side wall and liquid can be reached the point of coagulative necrosis(70° C)with covered by microwave thermal field.Histopathology of control group revealed normal bladder epithelial cells and intracellular structural integrity,the morphology of lamina propria and muscle cell integrity;experimental group revealed bladder wall epithelial cell degeneration and necrosis,and lamina propria and muscular layer of normal tissue structure were completely disappeared.Conclusions Microwave thermal energy was transmitted in the liquid medium by thermal convection,and the distribution of thermal field in homogeneous liquid medium was regionally and uniformity.Microwave ablation can be fitted for the treatment of cystic lesions.