Magnetic resonance measurement of ultrasound properties

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).