The Imaging Study Of MRI-Guided High Intensity Focused Ultrasound Surgery Of Rabbit Liver

BackgroundHigh Intensity Focused Ultrasound is originated in the 1990s, which is a noninvasive technique of solid tumor treatment. Its mechanism is to gather the low-energy of ultrasound in vitro at the target in vivo using the ultrasonic penetrativity and the characteristics of focus, and to make the tissue coagulative necrosis through creating transient high temperature (60-100℃), cavatition erosion and mechanical effects at target area. During the HIFU treatment process, the imaging monitoring is the key element. MRI have the advantages of high resolution of soft tissue,,multi-parameter,multi-functional imaging,noninvasive temperature measurement and non-ionizing radiation, which have been pay more attention by many scholars as a new monitoring means of HIFU. In recent years, MRI-guided HIFU system has been developed abroad. Hynynen, Peter, Tempany has been using the system treat breast fibrous tumor, breast cancer, uterine fibroids and other diseases, which achieved good results. However, the current study and clinical application is limited to the organs which are not affected by breathing. So I chose MRI-guided HIFU made by Chongqing HIFU Technology Co., Ltd to study the rabbit liver in vivo and the rabbit liver VX2 tumor.ObjectiveTo investigate the feasibility and accuracy of the MRI-guided HIFU injury of the liver in vivo, and to explore the parameters and conditions of MRI in the evaluation of HIFU treatment. Then using the condition to observe the MRI images of the vx2 tumors which was been treated by HIFU, and to hope that this study can lay the imaging foundation for the treatment of liver cancer by MRI-guided HIFU.Materials and methods1 Normal rabbit liver in vivo experimentsMRIgHIFU system was used (frequency-1.0MHz, focal length-150mm). Normal liver tissues in vivo of New Zealand white rabbits were used as materials. Before exposure, scan the TSE sequence T1WI,T2WI,PDWI to observe the MRI images of rabbit liver. T1WI images were used as location maps, and chose pre-irradiation levels to be exposed by HIFU. Exposure parameters: ultrasound power were 300w,250w,200w, exposure time were 30s. Each power irradiate 10 rabbits, and chose 1 target in each rabbit liver. Immediately after exposure, scan the T1WI,T2WI,PDWI again, and scan the TSE sequence enhanced T1WI. And then observe the changed signals of these images and measure the regions. Take the lesion for HE staining, and observe the morphological changes under optical microscope. All data were analyzed by SPSS 11.5 statistics package.2 VX2 tumor in rabbit liver experimentA piece of VX2 tumor tissue was implanted into rabbits'livers with operating knife blade splitting abdomen. Three weeks later, the models were used for HIFU treatment. Before exposure, scan TSE sequence T1WI,T2WI and enhanced T1WI, and observed the morphology, borders, signal characteristics and blood supply situation of the tumors. T1WI images were used as location maps, and chose pre-irradiation levels to be exposed by HIFU. Treatment plan: dot irradiation, ultrasound power: 250w, exposure time: 10s, each dot was been irradiated 2 times. The interval between each irradiation was 10s, and there was no spacing distance between each dot. The whole tumors were irradiated by deep-shallow,dot-line-side-block mode. Immediately after exposure, scan the T1WI,T2WI,enhanced T1WI again, and observed the morphology, borders, signal characteristics and blood supply situation of the tumors. Then killed the rabbits, took the tumors tissue for TTC staining, pathological biopsy, HE staining and observed the morphological changes under optical microscope.Result1 There were all 30 dots in rabbits'livers exposed by HIFU. 30 lesions on plain T1WI were hyperintense , elliptical or triangular, and the border was clear. And the lesion area on T1WI highly correlated with gray practical necrosis (P>0.05). The lesions on T2WI(18) and PDWI(3) were slightly hypointense, and the border was less clear. The other dots did not changed on MRI images. With the increase in radiation power,The signal difference of the lesion on MRI images and the normal liver tissue increased. which is that the greater the energy is ,the obvious the lesions are. Compare the T1WI and T2WI,the signal difference and contrast on T1WI was higher than that on T2WI,which is that the lesions on T1WI are more evident than that on T2WI..30 lesions on enhanced-T1WI were all without enhanced, Among them, the no enhancement area of 17 lesions were greater than the area of gray necrosis, and the difference had statistical significance. When the power was 300w, 8 dots had hyperintense area in no enhanced regions on enhanced T1WI images, and the area of it was corresponded well with the hyperintense area on plain T1WI. The result of biopsy showed the lesions were all coagulative necrosis.2 There were 20 VX2 tumors of rabbits'livers treated by HIFU. Immediately after exposure, the MRI images showed that the border of the tumors were clear, the signal of all the tumors increased on T1WI, and among them 14 tumors showed higher signal region in the center. On T2WI there were 5 tumors which signal degraded, 3 tumors increased and other tumors had no changes. On enhanced T1WI, there were 17 tumors had no enhancement, and the boundary between the tumor and the normal liver was clear. There was a little enhancement in 3 tumors'margin. And 3 rabbits'skin had been damaged. Plain T2WI showed the skin was thickened and stratified, the signal increased with low-signal lines in it. Plain T1WI showed he skin was thickened, but the signal did not changed obviously. Then to open the abdomen, the tumors were round or oval, yellow-white. In the central part of some tumors showed sorrel hemorrhage. There were 17 tumors which can not be stained by TTC, and the boundary was sharp. But the periphery of another 3 tumors was stained by TTC. Under light microscopy multiple tumors were coagulation necrosis.Conclusion1 The rabbits'liver in vivo and the VX2 tumors of rabbits'livers can be located precisely by the MRI-guided HIFU system, and the macroscopic damages can be made by the system also.2 Breathing constructed defect can be avoided by using TSE sequence, which could be used to monitor HIFU treatment.3 Through MRI plain scan and enhanced scan, the extent and scope of the tissue injury can be evaluated by observing signal changes of the target area. And the enhanced scan can more accurately respond the scope of the tissue injury.4 This study showed the feasibility of the liver tumor treatment by MRIgHIFU.