A system and method for medical treatment of tissue using ultrasound. The system comprises a probe having an array of transducer elements, an ultrasound waveform generator adapted to generate at least one electrical ultrasound signal, and a plurality of phase controls, each coupled to the ultrasound waveform generator and adapted to generate from the electrical ultrasound signal a phase-shifted drive signal that is coupled to an associated transducer element. The drive signal is effective to control grating lobe foci emitted by the array. The method employs the system.