| Objective:Based on the principle of microwave ablation and the characteristics of different degrees of edema response zones formed by spinal metastases,the aim of this study is to investigate the effect of vertebral water content on the determination of ablation zone,transverse diameter and longitudinal diameter after microwave ablation,and the correlation between them.In order to provide experimental basis for the selection of appropriate ablation methods and parameters for the treatment of spinal metastases by microwave ablation in clinical practice,and to achieve the best ablation range.Materials and Methods:(1)In vitro simulation model: Fresh egg yolk liquid with different water contents was prepared as experimental material and dissolved for 20 s,30s and 40 s at a power of 45 W.The experiment was repeated for 3 times.The main components of egg yolk liquid were fat and protein.In vitro models with different water contents were established by adding normal saline.When microwave ablation was performed,egg yolk liquid solidified and changed color with the increase of temperature.(2)In vitro vertebral body model: Fresh isolated pig vertebral bodies were used as experimental specimens,and the sections of the vertebral bodies were sealed with hot melt glue and divided into three groups: A,B and C;The specimens in group A were not treated as the control,and the specimens in group B and group C were injected with 0.3ml and 0.5ml normal saline along the center of the vertebral body,and the specimens in each group were ablated for 20 s,30s and 40 s at the power of45 W.After the ablation,the vertebral body was dissected along the ablation needle path,and the shape of the ablation area and the ablation boundary were observed,and the maximum transverse and longitudinal diameters were measured with vernier calipers.All data were recorded accurately,and the ablation area(S)and isoperittance(R)were calculated.The experiment was repeated three times,and the mean and standard deviation were calculated.A total of 137 ablation sites were completed.Results:1.In vitro simulation model: After the ablation,it can be observed that all the ablation foci are roughly ellipsoid,and the boundary between them and the surrounding non-ablation yolk liquid is clear.There were obvious differences in the ablation ranges of egg yolk liquid with different water contents at the same ablation time,and the difference was most obvious when the ablation time was 40 s.2.In vitro vertebral body model: immediately after ablation,the vertebral body was dissected along the ablation needle path.It was observed that the section shape of all ablation areas was roughly oval,the gray brown area of ablation area was necrosis and coagulation area,the surrounding normal tissue was dark red,and the boundary between ablation area and normal tissue was clear.With the increase of water content,the circular shape of the section of the ablation area is better under the same ablation conditions.The roundness of the samples with the same water content was better with the extension of ablation time.3.For comparison between groups,there were statistical differences in the maximum transverse diameter,maximum longitudinal diameter and ablation area of vertebral bodies with different water content at each time point.For intra-group comparison,the maximum transverse diameter,maximum longitudinal diameter and ablation area of the three groups at20 s were analyzed by ANOVA,and the p values were less than 0.05,and the differences were statistically significant.LSD was used for pairwise comparison within the group,the maximum transverse diameter A/C,the maximum longitudinal diameter A/B and A/C,and the ablation area were compared in pairs p < 0.05,and the differences were statistically significant.It can be considered that the maximum transverse diameter A < C,the maximum longitudinal diameter A < B < C,and the ablation area A < B < C.The maximum transverse diameter at 30 s was tested by Welch,p=0.00 < 0.05.A/B was statistically different from A/C by Tambane’s T2.The results of variance analysis of the maximum longitudinal diameter and ablation area showed that the maximum longitudinal diameter p=0.036 < 0.05,the ablation area p=0.000 < 0.05.LSD was used for pairwise comparison,the maximum longitudinal diameter A/C and ablation area p < 0.05,the difference was statistically significant.Ablation area A < B < C.The results of variance analysis showed that the maximum transverse diameter p=0.020 < 0.05,the ablation area p=0.000 < 0.05,the difference was statistically significant.LSD was used to compare the differences within the group,the maximum transverse diameter A/C and B/C and the ablation area p < 0.05,the difference was statistically significant.The maximum longitudinal diameter(p=0.078 > 0.05)was tested by Welch’s test,and the difference was not statistically significant,so no pairwise comparison within the group was performed.The maximum transverse diameter(A < C,B < C)and ablation area(A < B < C)could be considered.There was no statistically significant difference in maximum longitudinal diameter within the group.Conclusions:1.Through this experiment,it can be observed that under the constant power of 45 W and different ablation time(20s,30 s,40s),all the vertebral models with different water content after MWA were in the shape of the ablation area,the shape of the ablation area was oval,the protein coagulation and cell degeneration and necrosis in the ablation area were gray brown,and the surrounding non-ablated tissue was dark red,and the boundary between the two was clear.No carbonization zone was observed along the ablation needle path.2.Isoperimetry: The results of this experiment show that the isoperimetry R decreases with the increase of water content when the ablation time is 20 s at a constant power of 45 W.When the ablation time was 40 s,with the increase of specimen water content,the increase of isopexy was closer to 1,and the roundness was better.For vertebra with the same water con tent,with the extension of ablation time,the increase of constant frequency R is closer to1,and the roundness is better.3.Within a certain range,under the same ablation condition,the ablation area increased with the increase of water content,and there was a positive correlation between them.The maximum transverse diameter increased with the increase of water content,and the changes were more significant with the increase of water content at 30 s and 40 s ablation time.The maximum longitudinal diameter increased significantly with the increase of water content when the ablation time was 20 s and 30 s.At the ablation time of 40 s,the longitudinal diameter did not change significantly within the group,and the difference was not statistically significant.By comparing the mean ± standard deviation,it is reasonable to believe that water content is one of the factors affecting the ablation area,and the effect of water content on the transverse diameter of the ablation area is significantly greater than that of the maximum longitudinal diameter.4.Within a certain range,the transverse diameter,longitudinal diameter and ablation area of vertebral specimens with the same water content increased with the extension of ablation time,showing a positive correlation.In this experiment,when the ablation power was 45 W,the maximum transverse diameter and maximum longitudinal diameter of the vertebral body with the same water content increased significantly when the ablation time was over 30 s. |
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