Development of 1.5D cylindrical HIFU phased array

High intensity focused ultrasound, HIFU has been used to non-invasively treat human tumors, such as uterine fibroids, prostate cancer, breast cancer, liver tumor, and brain tumor. However, the tumor in some organs can be moved by human breathing and heart beat, which may cause the ablation and damage of normal tissues during the sonication of HIFU. The purpose of this study was to develop a HIFU phased array for tracking the moving tumors. In the initial design, the array had a center frequency of 1.0 MHz and 512 elements that allowed symmetric control. PZT-4 1-3 composites were formed via the ldquodice and fillrdquo technology and then shaped into a cylindrical structure. The results simulated by Field II demonstrated that the array in water had a dynamic focusing range from 145 mm to 175 mm in Depth and a steering range from -15 mm to 15 mm in azimuthal direction with respect to the center of the array. A prototype of the array was fabricated. The aperture of the array was 15 cm by 12 cm and the radius of curvature was 15 cm. The impedance of each channel (a pair of elements) was measured and the average was 1500 Ohm. Surface acoustic intensity up to 12.6 W/cm² was applied to one piece of cylindrical PZT4-composite consisting of 22 elements for 50 minutes, and the temperature of the composite was not observed to rise appreciably. A 256-channel amplifier was utilized to drive the array without impedance matching in water and the water spring was observed at the natural focus of the array when the driving signal to each channel was zero-phase at 0.9 MHz. The phase control and impedance matching circuits for each channel are being designed.