Microwave Ablation Of Liver VX2 Tumor:Experimental Study With Intravoxel Incoherent Motion Diffusion-weighted Imaging

Purpose: To evaluate the value of intravoxel incoherent motion diffusion-weighted imaging in the treatrment response of microwave ablation（MWA） of the rabbit liver VX2 tumors.Materials and Methods: 27 rabbits of VX2 tumors were constructed successfully, and were randomly divided into 3 groups（group A, group B,group C）. All the 27 tumor-bearing animals underwent MWA. All percutaneous procedures of MWA were performed under CT guided. All rabbits underwent MRI exams on 1, 2, and 4 weeks respectively after MWA. a group of corresponding experimental rabbits were sacrificed and pathology was performed immediately after the MR imaging session, measuring the apparent diffusion coefficient（ADC）, true diffusion coefficient（D）,pseudodiffusion coefficient（D*）, and perfusion fraction（f） of pre- and post-MWA lesions of VX2 tumors to discriminate necrosis tissue, viable tumor, granulation tissue and normal liver tissue, followed by least repeated measurement data analysis of variance（ANOVA） was applied to compare parameters, followed by least significant difference（SNK） tests for multiple comparisons of quantitative data. p < 0.05 was considered statistically significant.Results: All the 27 rabbit liver models of VX2 tumors were treated with MWA successfully, One died because of anesthetized overdose, two died of local recurrent with peritoneal metastasis, one died because of the ablation needle too many times, the liver capsule rupture, and one was excluded due tointestinal obstruction after MWA. 22 rabbits of VX2 tumors in the follow-up process. Macroscopically, central appeared necrotic lesion, granulation tissue which is around the necrotic MWA lesion, some viable tumors appeared as nodule at the periphery of MWA, central liquefaction necrosis was found in larger lesion. Peripheral inflammatory reaction zone early were consistent with granulation tissue, inflammatory tissue or edema, the inflammatory cell were infiltrated, and fibrous capsule were presented. The mean ADC, D, D*and f values of tumor before MWA were（1.39±0.17）×10^-3mm²/s,（0.95±0.14）×10^-3mm²/s,（41.48±13.54）×10^-3mm²/s,（23.43±3.63）% respectively;The mean ADC, D, D* and f values of liver parenchyma before MWA were（1.82±0.11）×10^-3mm²/s,（1.26±0.13）×10^-3mm²/s,（81.58±17.99）×10^-3mm²/s,（21.67±4.19）% respectively. The differences between tumor and normal liver parenchyma before MWA at ADC, D, D* and f values were statistical significance respectively（P<0.05）. After MWA, the mean ADC, D, D*, and f values in viable tumor tissue were（1.40±0.10）×10^-3mm²/s,（0.92±0.15）×10^-3mm²/s,（39.98±10.11）×10^-3mm²/s,（19.64±4.53）%; The mean ADC, D, D* and f values in necrosis tissue were（0.74±0.42）×10^-3mm²/s,（0.56±0.31）×10^-3mm²/s,（20.18±5.79）×10^-3mm²/s,（13.77±5.10）%; The mean ADC, D, D* and f values in inflammatory hyperemic reaction were（1.97±0.18）×10^-3mm²/s,（1.51±0.30）×10^-3mm²/s,（88.90±16.49）×10^-3mm²/s,（26.35±5.96）%; The mean ADC, D, D* and f values in normal liver parenchyma were（1.77±0.19）×10^-3mm²/s,（1.25±0.16）×10^-3mm²/s,（78.80±19.06）×10^-3mm²/s,（22.68±4.62）%; The ADC, D, D* and f values in different tissues afrer MWA showed statistical significance（P<0.05）.Conclusions: The IVIM-DW derived f, D and D* parameters have the potential to indicate therapy response after MWA treatment, and it was usefulin detecting different tissues after MWA, and it is possible to be biomarker in the assessment of treatment response of hepatic carcinoma after MWA.