Study Of High Intensity Focused Ultrasound Ablation For Liver Tumors Adjacent To The Abdominal Aorta In The Rabbits

Liver cancer is one of the most common malignancies worldwide,especially in China. The mortality rate of liver cancer is the second most inmalignant tumors. Currently, surgery is the choice of treatment for livercancer in select cases, however, most of the patients were at the advancedstage when the diagnosis was made. Only20percent of the patients aresuitable for surgery because of the tumor location, poor liver function.Therefore, minimally invasive therapies are used in treating patients withliver cancer, such as radiofrequency ablation (RFA), transcatheter arterialembolization(TAE), transcatheter arterial embolization chemotherapy(TACE), percutaneous ethanol injection (PEI), laser, microwave and so on.For the tumors closed to the inferior vena cava, hepatic portal vein, it isdifficult to treat with surgery, nor with RFA. Since high intensity focusedultrasound (HIFU) can ablate the target tissue accurately and efficientlywithout damage to the surrounding normal tissues. Therefore, this techniquemay offer the patients alternative treatment.In this study, the rabbit model of VX2liver tumor adjacent to abdominal aorta within1cm is established. The rabbit liver tumor has beenablated completely by MR-guided high intensity focus ultrasound ablation.The hemodynamic changes and the effects of HIFU on large vessels wereobserved. We also studied the “heat-sink” effect of HIFU for tumor ablationand investigated the tumor rabbit’s survival.Objectives1. To establish the rabbit model of VX2liver tumor adjacent to theabdominal aorta for choosing the optimal time for HIFU ablation.2. To explore the impact of HIFU ablation of the liver tumor adjacent tothe aorta using MRI-guided high intensity focused ultrasound (HIFU) bycomparing the hemodynamic parameters a before and after HIFU.3. To evaluate the safety and efficacy of HIFU ablation for the VX2liver tumor near hepatic main blood vessels of rabbits by analyzing thedosimetry, MRI, pathological changes and survival.Methods1. A piece of VX2tumor was implanted in the hepatic hilum in45rabbits by surgery. All the rabbits underwent MRI on the14th,21st and28thdays after implantation to observe the rate of tumor formation, the tumorvolume and the distance between the tumor and abdominal aorta.2. The model of VX2liver tumor adjacent to the abdominal aorta wasestablished successfully in43rabbits. The ablation of the liver tumor wasperformed using MRI-guided HIFU. Color Doppler ultrasonography was used to observe if the abdominal aorta was filling and to measure the peaksystolic velocity (PSV), the mean velocity (Vmn), the resistance index (RI)and the pulsatility index (PI) of abdominal aorta before and0h,2h and6hafter ablation. Pathological changes of the abdominal aorta was observedbefore and0h after ablation.3．The ablation volume and Energy-Efficiency Factor (EEF) of32ablated rabbits was analyzed. The tumor change after HIFU was comparedwith before by MRI and pathology. The survival in HIFU group and thecontrol group was observed.Results1. The survival rate and tumor formation rate were92.11%(41/45) and97.12%(39/41), respectively. In MRI, the tumor manifested as high signalon T2WI and enhancement on VIBE FS TlWI was observed on the14th and21th day after implantation. Ring enhancement of tumor with noenhancement in tumor center was observed on the21th day afterimplantation. The tumor volume increased and the distance between tumorand aorta was decreased with extension of time(P＜0.05). The optimal timefor HIFU ablation was the21th days after implantation.2. After ablation, the blood flow was normal in the abdominal aorta.No stenosis, collapse and occlusion were observed. The PSV, Vmn reducedand RI, PI increased significantly at0h (all P＜0.05) after HIFU andrecovered to the normal level (all P＞0.05) at6h after ablation. The pathologic results showed no injury of the abdominal aorta0h after ablation.3．Both pathology and imaging showed the rabbit liver VX2tumoradjacent to the abdominal aorta was completely ablated and EEF was25.72±11.40J/mm3. The HIFU survival was significantly longer thancontrol group with statistic differences (P <0.05).Conclusion1. Establishing model of VX2liver tumor adjacent to rabbit abdominalaorta by implanting a tumor fragment with surgery is feasible and reliable,which can provide experimental model for HIFU treatment of liver cancer.2. HIFU ablation of liver tumor adjacent to the abdominal aorta cancause transient hemodynamic changes and has no impacts on the vascularwall.3. HIFU ablation is safe and effective in rabbit VX2liver tumor closedto abdominal aorta and the survival improved significantly.