Reduction of the thermo-acoustic lens effect during ultrasound-based temperature estimation

The use of high intensity focused ultrasound (HIFU) for a range of therapies requires improving real-time monitoring methods of the treatment. The feasibility of real-time two-dimensional temperature estimation from pulse-echo diagnostic ultrasound measurements has been demonstrated. It has been shown, however, that ripple artifacts due to the thermoacoustics lens effect severely corrupt the temperature estimates behind the heated region. We propose a new imaging technique based upon a compound technique found in some diagnostic ultrasound scanners in order to improve the temperature estimation behind the heated region. Conventional beamforming in the transmit mode is replaced by a set of N compounded plane wave emissions for several subapertures. Following estimation of the axial displacement between emissions of identically angled plane waves, the N two-dimensional temperature maps are averaged resulting in an improved temperature estimation behind the heated region. We discuss the choice of the N compound angles as well as the number and size of the subapertures. In addition, we demonstrate how the reduction of the ripple artifact variance depends on these factors and can be optimized for a given experimental setup and desired frame rate.