Focus-shift compensation in high intensity focused ultrasound using the time reversal method

The actual focal point can deviate from the desired point in the traditional treatment of high intensity focused ultrasound (HIFU). In order to investigate the focus-shift compensation effect of HIFU by the time reversal method, we solved the Westervelt equation using the finite difference time domain method, and established a numerical model of HIFU field in layered tissues. Numerical simulation shows that the maximum deviation of the focus point is decreased to 1.6 mm after using the time reversal method. The thickness of fat layer and the source intensity have negligible effects on the time reversal focusing accuracy, while the deviation of the focus decreases when lowering the F number (the ratio of focal length and aperture). The study indicates that when the nonlinearity and absorption parameters change in the range of that of human tissue, the time reversal method can compensate the focus-shift effectively and has a better focusing quality.