Development of a Spherical Ultrasound Transducer for Transcranial Low-Dose Ultrasound Hyperthermia Used in Brain Tumor Nanodrug Delivery

Previous studies showed that low-dose focused ultrasound hyperthermia (UH) could enhance the delivery and therapeutic efficacy of nanodrug for brain metastasis of breast cancer. In this study, our purpose is to design an ultrasound transducer that can be used for clinical application for brain tumor nanodrug delivery. Computer simulation has been used to calculate the pressure field, temperature distribution and thermal dose in the brain for different parameters of a spherical array ultrasound transducer. An ultrasound transducer with 112 disc elements (1 MHz, 2 cm in diameter) was constructed and its heating ability was characterized using a skull phantom filled with hydrogel. The simulation results showed that the position of peak pressure was slightly offset when the transducer was mechanically moved 3 cm away from the center point in all directions. There was no significant side-lobe developed when the transducer was moved away from the center 2 cm. Temperature distribution showed that the heating zone was an ellipsoid with temperature higher than 42 degrees C for a maximum intensity of 121 W/cm(2). Phantom experiment showed that the 42 degrees C color-changeable hydrogel would turn to be white at the focal point when the transducer was moved 2 cm in all directions with an electrical power 55 W. A spherical ultrasound phased array was developed and characterized, and the results showed that this ultrasound transducer has the potential used in transcranial short-time ultrasound hyperthermia for brain tumor nanodrug delivery.