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

We present results from realtime feedback control of single-andmultiple- focus phased array heating patterns based on ultrasound thermography.The results illustrate several important aspects of realtime control of phasedarray heating patterns as they are envisioned to be used in noninvasive,image-guided thermal therapy applications. First, complex, multiple-focusheating patterns require multi-point, noninvasive temperature feedback that maynot be easily available using thermocouple or other invasive proibes. Second,multiple-focus pattern synthesis must be optimized to maintain the highestefficiency of the phased array driver in order to achieve the controlobjectives. This has led to the development of a dynamic power reallocationalgorithm for realtime management of the power share of each focus accoring tomaximize its heating rate. Third, realtime integration between the feedbackthermography and array driver control with high spatial and temporal resolutionis necessary, especially for short exposures used in ablative treatments. Theseaspects are well illustrated by the results shown: 1) realtime thermography atframe rates up to 100 fps, 2) realtime multiple-focus pattern resynthesis withupdate rates up to 1000 patterns per second, and 3) an intelligent dynamic powerreallocation scheme to distribute the available driving power according to thecollective needs of the individual foci in the multiple-focus heating patterns.Without this dynamic power reallocation, the standard multiple-focus patternsynthesis may produce low-efficiency driving patterns that may fail to achievethe control objective at the some or all control points in the heating pattern.