Optimal control point distributions for waveform diversity.

Abstract

Waveform diversity is a method for tumor heating with ultrasound phased arrays that extend the concept of multiple focusing to achieve an optimal sequence of power depositions. Waveform diversity minimizes the power deposited at control points in normal tissue while maximizing the power at control points in the tumor through an approach that employs semi‐definite programming. As with other spot scanning and multiple focusing techniques, the performance of waveform diversity depends on the location of the control points. For example, single spot scanning is limited by intervening tissue heating, so the ideal spot scanning approach in large tumors focuses on the back half of the tumor and allows intervening tissue heating to fill in the remaining tumor region. In contrast, waveform diversity combined with mode scanning tends to preferentially deliver heat beyond control points placed in the tumor. In an effort to exploit this feature, the energy delivered to control points on the front face of the tumor is maximized, and the energy delivered to control points along the tumor axis and directly behind the tumor is minimized. Results show that this control point distribution applied to waveform diversity combined with mode scanning achieves conformal heating in a 3‐cm‐diameter spherical tumor model that is heated by a 1444 element spherical section array.