Design and Ex Vivo Evaluation of a 3D High Intensity Focused Ultrasound System for Tumor Treatment with Tissue Ablation

Abstract

This paper describes the design, construction, and evaluation of a three dimensional (3D) ultrasound system to be used to treat different kinds of tumors using high intensity focused ultrasound (HIFU). The system consists of two major parts: an ultrasonic therapy part and a treatment planning part. The ultrasonic therapy part consists of an ultrasound bowl shaped transducer (made from Lead Zirconate Titanate (PZT) and has a resonance frequency of 0.5 MHz), a lossless electrical impedance matching circuit built to ensure maximum electrical power delivery to the transducer, a function generator, and a high power amplifier. The ultrasonic therapy part is responsible for generating a high-power focus at the location of the geometric focus of the bowl shaped ultrasound transducer. The treatment planning part consists of three stepper motors (responsible for moving the setup in the x- y- and z-directions), three high-voltage high-current darlington arrays (to supply the stepper motors with the required voltages and currents), and a C# software to perform the treatment planning. To assess the movement of the treatment planner, each of the three stepper motors was moved forward and backward from end to end. Then the treatment planner was successfully driven to cover cubes of dimensions of 1 x 1 x 1 cm³, 2 x 2 x 2 cm³, 4 x 4 x 4 cm³, and 8 x 8 x 8 cm³, with step sizes 0.5, 1, 2, and 4 mm, respectively. Ex vivo experiments using fresh bovine liver were performed and indicated the capability of the system to generate lesions both on- and off-axis. Lesions at different depths were successfully generated at the intended locations. Temperature distributions were recorded both inside and outside the lesion and indicated that the temperature reached about 60°C inside the lesion and remained below 39°C outside it.