Abstract: A method includes determining, during a calibration phase without application of ultrasound waves, a per-pixel magnetic field gradient of a magnetic field that is generated using a calibration drive signal applied to a magnetic coil; generating, during a treatment phase, a magnetic field gradient that is applied to a treatment area by using a treatment drive signal applied to the magnetic coil, wherein treatment drive signal is different from the calibration drive signal; determining, based on the treatment drive signal applied to the magnetic coil, per-pixel phases of a treatment image of the treatment area, wherein the per-pixel phases of the treatment image are based on spin displacement at each pixel resulting from the applied ultrasound waves; and adjusting, for each pixel of the treatment image, the per-pixel phases of the treatment image based on the per-pixel magnetic field gradient for a corresponding pixel, to obtain a gradient-adjusted treatment image.