| Objective: The purpose of this study was to determine if HIFU issecure and effective for the treatment of intracranial neoplasm by observingpathological regression at the focus in normal New Zealand Rabbits' braintissue after ablation. Methods: The CZF-II type ultrasound therapeutic apparatus was usedand its maximum acoustic power (5 watt) was selected with thecorresponding most suitable parameters of the equipment. The experimentwas carried out in two steps. Firstly, by using the same total time of HIFUexposure, we took different divided time to sonicate on localized braintissue of 24 New Zealand Rabbits for several times, observing the rabbits'reaction and living status. All animals were killed after 5 weeks. Then weapplied TTC stain to observe the gross changes and HE stain to observehistological changes under microscope. Then according to the results offirst step, we selected suitable doses of exposure to ablate other 12 rabbits'brain tissue, and sacrificed them successively at the 1st, 3rd, 7th, 14th, 28thand 60 days(d) after sonication, observing target lesions grossly andmicroscopically to identify the biological characteristic and pathologicchanges. The ultrastractural changes were also observed immediately aftersonication. Results: During the observation period, the rabbits' living status wasapparently getting worse when the time was ≥ 20 second(s) after eachexposure. The gender and times of exposure were not correlated with livingstatus. According to our observation, the rabbits could tolerate the dose ofHIFU exposure <5W×20s, but histological study indicated that the bestexposure time was 5—10s. Adopting the same experimental condition, wetook the 5s and 10s for each exposure time in further studies. Differentranges of lesions were produced after different exposure time grossly,especially on 28d, although microscopically the lesion were almost thesame in early period. Finally the 10s sonicated area regressed to scar of glia,but no apparent lesion was found in the 5s area. Ultrastractural examinationshowed the integrity of cell and vascular structure were destructed in 10sarea, but remained intact in 5s area. Conclusion: The toleration to HIFU exposure for brain tissue iscorrelated with single dose of sonication, and independent from the genderand times of exposure. HIFU could ablate deep localized brain tissue withlittle effect on the superficial brain tissue. The restoring mode of sonicatedlesion is correlated with exposed doses, and it is reversible when usingsuitable dose of exposure. In conclusion, it is secure and effective to usesuitable dose of HIFU in the treatment of intracranial neoplasm and someexperimental data are provided for future clinical investigation.
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