An apparatus (500, 600) comprising an
ultrasound transducer element (300) for generating an
ultrasonic beam (302) through a target zone (308, 538). The
ultrasonic beam has an
ultrasound frequency. The apparatus comprises a magnetic
resonance system (502) with a resonant frequency modulator (542, 544, 516) for modulating a magnetic
resonance frequency relative to a magnetic
resonance of molecules in the target zone at the
ultrasound frequency. Instructions cause a processor to repeatedly generate (100, 204) first gradient commands (562) which cause a
magnetic field gradient coil to generate a first gradient
magnetic field (710, 810) through the target zone. The gradient
magnetic field has field lines directed in a first direction (304). The processor repeatedly modulates (102, 206) the magnetic resonance frequency at the ultrasound frequency, generates (104, 208) ultrasound commands (566), acquires (106, 210) magnetic resonance data from the target zone, and generates (108, 212) second gradient commands (564).