Abstract: Objective   To investigate the efficacy of multi-frequency focused ultrasound （MfFU） in the treatment of alveolar hydatid disease in mice.  Methods   Thirty Kunming mice infected subcutaneously with alveolar protoscoleces were divided into 3 groups randomly of 10 mice each and irradiated with different intensity of MfFU. Mice in the experiment groups B and C were irradiated only once for 5 min and group A served as control. The irradiation power of the 3 transducers in the low-power group （group B） was 4 W+4 W+5 W；that in the high-power group （group C） was 10 W+11 W+10 W. After the irradiation，the morphological change of alveolar tissues was observed with transmission electron microscope. The survival rate of protoscoleces was evaluated with methylene blue staining. The mitochondrial content in the alveolar tissues was detected with laser confocal microscope. The Coomassie brilliant blue staining and succinate dehydrogenase （SDH） kit were applied for measuring the amount of general proteins and the activity of succinate dehydrogenase of the alveolar hydatid cyst respectively.  Results   After irradiated by MfFU，transmission electron microscopy showed that in groups B and C the cells on the germinal layer decreased. The mitochondria swelled or broke. The endocytoplasmic reticulum became swollen markedly. The karyotheca looked unclear. The microvilli shortened or disappeared. All the damages in group C displayed more seriously than in group B. The survival rate of protoscoleces in groups B （70.50%） and C （59.83%） was statistically lower than that of group A（82.33%） （P<0.05）. And there was also a statistical difference between groups B and C （P<0.05）. The amount of general proteins and the activity of SDH in groups B （3.07 mg/ml and 2.15 U/mg respectively） and C （2.87 mg/ml and 1.87 U/mg） were lower significantly than those in group A （3.83 mg/ml and 3.50 U/mg）（P<0.05），but no statistical difference between B and C （P>0.05）. The mitochondria content in groups B（105.46 a.u/a） and C（70.90 a.u/a） was lower than that in group A （133.45 a.u/a）. Group C showed statistical difference than A and B （P<0.05），but there was no statistical difference between A and B（P>0.05）.  Conclusion It is evident that the cysts of Echinococcus multilocularis in mice can be damaged by MfFU which shows certain curative effect.

Key words: Multi-frequency focused ultrasound, Echinococcus multilocularis, Transmission electron microscopy, Laser confocal microscopy, Succinate dehydrogenase