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

This article describes the design, construction, and evaluation of a three-dimensional (3D) ultrasound system to be used for the treatment of kidney tumors using high-intensity focused ultrasound (HIFU). The system consists of a therapeutic ultrasound delivery module (driver, power amplifier, matching circuit, and transducer (1 MHz)) and a 3D positioning module (stepper motors and microcontroller). The system includes software that designs a treatment planning according to the tumor coordinates. In order to verify the capability of the system for moving the transducer, the positioning module was successfully driven to cover cylinders of dimensions as large as 20 cm (diameter) x 10 cm (height) with step sizes as low as 0.05 mm. Several exposimetry experiments were done which showed close match between experimental and theoretical results. Ex vivo experiments were performed and indicated the capability of the system to generate a single lesion of 0.27 cm diameter and 0.45 cm length, as well as five lesions (each with a diameter of 0.3 cm) at prespecified locations. During the ex vivo experiments, temperature monitoring indicated an increase in temperature from 37 degrees C to about 60 degrees C inside the lesion, while outside it the temperature remained below 39 degrees C.