A nonlinear derating method for estimating high-intensity focal pressures in tissue

Abstract

Methods for converting high-intensity focused ultrasound (HIFU) pressure measurements made in water to values appropriate for tissue have considerable value in preclinical testing and treatment planning. Such “derating” methods are straightforward in the linear-acoustics regime, but are much more difficult at higher powers. In this study, a nonlinear derating method is used to estimate focal pressure in a tissue phantom. The on-axis pressure in water was recorded using a hydrophone. Fourier transformation of the recorded pressures was performed and the resulting modal amplitudes were reduced using a combination of “source scaling” (measurements in water performed at a lower source pressure than in tissue phantom) and “endpoint scaling” (amplitudes reduced at the target location). The reduced modal amplitudes were used in the convolution term of the evolution equation to determine the pressure in tissue. The focal pressure waveform estimated by this method was compared with a direct measurement in a tissue phantom. The results show that, with the proper combination of source and endpoint scaling, focal pressure in a tissue phantom can be reproduced by derating within 15% error.