Realtime control of multiple-focus phased array heating patterns based on noninvasive ultrasound thermography

We present results from realtime feedback control of single- and multiple-focus phased array heating patterns based on ultrasound thermography. The results illustrate several important aspects of realtime control of phased array heating patterns as they are envisioned to be used in noninvasive, image guided thermal therapy applications. First, complex, multiple focus heating patterns require multi-point, noninvasive temperature feedback that may not be easily available using thermocouple or other invasive probes. Second, multiple-focus pattern synthesis must be optimized to maintain the highest efficiency of the phased array driver in order to achieve the control objectives. This has led to the development of a dynamic power reallocation algorithm for realtime management of the power share of each focus according to maximize its heating rate. Third, realtime integration between the feedback thermography and array driver control with high spatial and temporal resolution is necessary, especially for short exposures used in ablative treatments. These aspects are well illustrated by the results shown: 1) realtime thermography at frame rates up to 100 fps, 2) realtime multiple-focus pattern resynthesis with update rates up to 1000 patterns per second, and 3) an intelligent dynamic power reallocation scheme to distribute the available driving power according to the collective needs of the individual foci in the multiple-focus heating patterns. Without this dynamic power reallocation, the standard multiple-focus pattern synthesis may produce low-efficiency driving patterns that may fail to achieve the control objective at the some or all control points in the heating pattern.