1.5D multi-elements phased array applied to high intensity focused ultrasound

High Intensity Focused Ultrasound (HIFU) has been used successfully to treat localized prostate cancer. The systems currently used involve fixed-focus therapeutic probes. This study describes a new probe able to electronically focus the ultrasound beam in the prostate´s sagittal plane. Its form is that of a section of a spherical shell containing 126 elements, all with the same area and arranged in a 1.5D configuration. Initially, simulations of the acoustic beam were undertaken to determine the ideal configuration of the array for dynamic focusing in a sagittal plane of 2×2 cm² in area centered on the geometric focus of the shell. An array containing 210 elements (with an inter-element spacing of 0.97 mm) was then built using a piezocomposite material. The section consists of a central, 11 mm-wide strip with 4 lateral strips of 5.5 mm, each containing 42 elements. To limit the number of electrically independent elements to 126 in total, the lateral strip elements are connected in pairs symmetrically with respect to the central strip. The array elements are arranged on a piezocomposite spherical shell of the same dimensions and properties as those of previously used probes. Power is supplied to the transducer elements from a 126-channel amplifier (2 W per channel). Simulation results and acoustic measurements show that this 126-element 1.5D array can be electronically adjusted to steer the focal point around the predefined 2×2-cm² area. The electroacoustic efficiency of this 126-element array is 40.44%, i.e. relatively low for this kind of material (which usually yields between 70 and 80% with single-element probes)