Two-dimensional ultrasound phased array design for tissue ablation for treatment of benign prostatic hyperplasia

Abstract

This paper describes the design, construction and evaluation of a two-dimensional ultrasound phased array to be used in the treatment of benign prostatic hyperplasia. With two-dimensional phased arrays, the focal point position can be controlled by changing the electrical power and phase to the individual elements for focusing and electronically steering in a three-dimensional volume. The array was designed with a steering angle of +/-14 degrees in both transverse and longitudinal directions. A piezoelectric ceramic (PZT-8) was used as the material of the transducer, since it can handle the high power needed for tissue ablation and a matching layer was used for maximum acoustic power transmission to tissue. Analysis of the transducer ceramic and cable impedance has been designed for high power transfer with minimal capacitance and diameter. For this initial prototype, the final construction used magnet compatible housing and cabling for future application in a clinical magnetic resonance imaging system for temperature mapping of the focused ultrasound. To verify the capability of the transducer for focusing and steering, exposimetry was performed and the results correlated well with the calculated field. Ex vivo experiments were performed and indicated the capability of the transducer to ablate tissue using short sonications. For sonications with exposure time of 10, 15 and 20 s, the lesion size was roughly 1.8, 3.0 and 4.3 mm in diameter, respectively, which indicates the feasibility of this device.

Optimization of ultrasound array designs for high intensity focused treatment of prostate cancer and benign prostatic hyperplasia

“…This choice of element dimensions means that Grating lobes will be generated at unwanted locations. It has been found that a value of Grating lobe that is 20% of the maximum intensity is acceptable as it will not lead to temperatures above 41°C at the location of the Grating lobes, unless excessive acoustical power is used [8][9][10].…”

“…Planar arrays are easier to dice, easier to acoustically match, and easier to electrically match. Previous effective flat arrays that were able to generate lesions in parts of the prostate include a two-dimensional (2-D) 8 9 8 phased array that was capable of electrically focusing and steering the ultrasound beam over a portion (less than half) of the prostate [8]. Another example is a 1.75-dimensional (1.75-D) 21 9 3 phased array that had the capability of focusing and steering the ultrasound beam at three different parallel planes inside the prostate [9,10].…”

Design and ex vivo kidney evaluation of a high-intensity focused ultrasound transducer and 3D positioner

“…Furthermore, a single channel power amplifier is needed to drive the single element transducer; however, multiple channels are needed for a 2D phased array. Although a 2D phased array can be electrically steered without the need to mechanically moving the array, the total steering angle is limited due to the formation of large grating lobes as the steering angle increases [9,13,14].…”

A 63 element 1.75 dimensional ultrasound phased array for the treatment of benign prostatic hyperplasia

“…Improvements over 1-D arrays for the treatment of localized prostatic cancer can be achieved. Many multi-dimensional ultrasound phased arrays have been designed and built for the treatment of prostate diseases; that includes a 1.5-dimensional (1.5-D) phased array [10] (a 1.5-D array consists of three individual linear array that can be driven individually or connected together to form a single linear array), a 1.75-dimensional (1.75-D) phased array [11] (a 1.75-D array consists of many individual linear arrays that are driven separately), and a two-dimensional (2-D) phased array [12]. The advantage with a multi-dimensional phased array is that it has the capability of focusing and steering in a 3-dimensional (3-D) representation of the prostate without the need to physically move the array.…”