A system for the realtime generation and control of multiple-focus ultrasound phased-array heating patterns is presented. The system employs a 1-MHz, 64-element array and driving electronics capable of fine spatial and temporal control of the heating pattern. The driver is integrated with a realtime 2-D temperature imaging system implemented on a commercial scanner. The coordinates of the temperature control points are defined on B-mode guidance images from the scanner, together with the temperature set points and controller parameters. The temperature at each point is controlled by an independent proportional, integral, and derivative controller that determines the focal intensity at that point. Optimal multiple-focus synthesis is applied to generate the desired heating pattern at the control points. The controller dynamically reallocates the power available among the foci from the shared power supply upon reaching the desired temperature at each control point. Furthermore, anti-windup compensation is implemented at each control point to improve the system dynamics. In vitro experiments in tissue-mimicking phantom demonstrate the robustness of the controllers for short (2-5 s) and longer multiple-focus high-intensity focused ultrasound exposures. Thermocouple measurements in the vicinity of the control points confirm the dynamics of the temperature variations obtained through noninvasive feedback.
Bibliographical noteFunding Information:
Manuscript received September 22, 2010; revised December 21, 2010; accepted January 24, 2011. Date of publication July 14, 2011; date of current version December 21, 2011. This work was supported in part by the National Institutes of Health under Grant EB009750 and Grant EB008191. Asterisk indicates corresponding author A. Casper and D. Liu are with the Department of Electrical and Computer Engineering, College of Science and Engineering, University of Minnesota, Minneapolis, MN 55455 USA (e-mail: email@example.com; liuxx293@ umn.edu).
- temperature control
- ultrasonic arrays
- ultrasonic imaging
- ultrasonic therapy