| Objective: To study thermal field characteristic of microwave radiation induced by implanted electrode in the spleen and to explore optimized parameters for massive ablation in the spleen with single electrode for establishing quantitative microwave ablation therapy in clinical treatment of secondary Splenomagely and hypersplenism.Materials and Methods: (1) In vitro experiment To explore optimized combination of tip length, energy output and radiation time in quantitative spleen ablation with single electrode, serial tests with different lengths of the exposed inner conductors (27, 36, 45, 54, 63, 72, 81, and 90mm), energy output (60, 70, and 80W), and radiation time (500, 600, and 700s) were tested. In vitro, temperatures of 206 spots/times with 65 times microwave radiation were measured in 4 canine spleens and 25 porcine livers, respectively. (2) Animal experiment Twenty healthy adult mongrel dogs were randomly divided into two groups, experimental group (n=14) and control group (n=6). Congestive splenomegaly, segmental portal hypertension, and hypersplenism were induced by ligation of the splenic vein and its collateral branches in both groups.Microwave ablation of the spleen was performed in experimental group only. With total energy of 18000J, microwave radiation combinations of 40W450sx 50W360s, 60W360s, 70W257s were selected. Temperature monitoring was done at 4 to 6 spatial spots in one radiation. Biopsy specimens obtained at different temperature spots were examined by light and electron microscopy to observe histopathological changes in situ. Microwave radiations were performed at 45 spots with temperature monitoring at 219 spots/times in 14 dogs. Ablation volumes were observed and calculated by a combination of gray-scale ultrasonography, color Doppler flow imaging with ultrasound contrast technique and three dimensional ultrasound at 1, 4 ,8 weeks after microwave ablation. Ablation volumes calculated by above method were compared with contrast-enhanced three dimensional MRI and were confirmed by pathological exam. (3) Clinical study Microwave ablations of the spleen were performed in 8 patients with secondary splenomagely and hypersplenism, seven during laparotomy and 1 percutaneously with ultrasound guidance. According to microwave ablated spleen volume, eight cases were divided into four groups: < 20% ( 2 cases ), 20-30% ( 2 cases ), 30-50% ( 3 cases ), and >50% ( lease ). Splenectomy was performed immediately in all cases of 30-50% group after microwave ablation. Ten patients with cirrhosis, portal hypertension, secondary splenomagely and hypersplenism were selected as a control group. Various spleen sparing limited portacaval shunt and portoazygous devascularization with ligation of the spleen artery were performed according to patients' condition. Results (1) In vitro experiment Shape of coagulation area could be altered by changing the length of the exposed inner conductor. Increase of the length of the exposed inner conductor changed coagulated shape from an elliptic sphere toa cylinder or a cone. Under fixed transverse axis of coagulation area, increase of longitudinal axis increased coagulated volume. Coagulation area could be enlarged by increasing output power and radiation time properly. Using a output power of 80W and radiation time of 600 to 700s, a large coagulated volume could be obtained in one radiation with exposed inner conductor lengths of 54mm, 63mm or 72mm. (2) Canine experiment Animal model of segmental portal hypertension, congestive splenomegaly and hypersplenism was induced by ligation of the splenic vein and its collateral branches in canine experiment. Splenomegaly could be maintained over 2 months after ligation of the splenic vein. Histopathological findings of those canine models confirmed congestive splenomegaly and hypersplenism. Temperatures in microwave ablation area decreased regularly from center (microwave electrode) to periphery. With same energy output, rapid temperature increase and larger coagulated volume could be obtained by increasing output power. A b...
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