球狀陣列式超音波換能器應用於非侵入式腦部短時間 熱治療之研究

Abstract

Abstract Background: About 40% of cancer patients develop brain metastasis and it is a major cause of mortality and mobility. Brain metastasis is prevalent in lung cancer, melanoma, and breast cancer. The standard managements of brain metastasis are chemotherapy, radiation therapy and surgery. Therapeutic ultrasound creates a new opportunity to treat brain tumor non-invasively. However skull and blood brain tumor barrier (BTB) are needed to be overcome. In this study, our purpose is to design an ultrasound transducer that can deliver enough energy through skull for short-time brain hyperthermia without damaging normal tissues. Material and Methods Rayleigh integral and secondary source model were used to calculate pressure field inside the brain at 1 MHz and 0.5 MHz, and then pressure were used to calculate the temperature distribution and thermal dose to identify treatment area for short-time brain hyperthermia. The transducer was mechanically moved to see the treatment area of 1 MHz home-made transducer for different location. Skull phantom and 42℃ hydrogel were further used to characterize the transducer. Results The simulation results showed that the position of peak pressure was slightly offset (<1mm) when the transducer was mechanically moved 3cm in X, Y or Z directions. There was no significant sidelobe when transducer mechanically moved 2cm in all directions. Temperature distribution showed that the shape of heating zone was an ellipsoid (2.2mm*2.3mm*3.9mm) with the temperature beyond 42℃ at a max intensity 119W/cm2 was used. Phantom study showed 42℃ hydrogel would change the color when the transducer was moved ± 2cm in y direction and +2cm in z direction and turned on with an electrical power 55W. Conclusion: An 1MHz sphere array transducer could successfully deliver enough energy with a low electrical reflection through skull phantom for short-time brain hyperthermia. The transducer can move ±1, ± 2 cm in x, y and z direction without developing significant side lobes, and the transducer is able to create a local hyperthermia.