This invention relates to a method and an apparatus of controlling a release of a material carried by ultrasound sensitive particles, the release being caused by irradiating the ultrasound sensitive particles with an ultrasonic pulse having acoustic properties selected so as to interact with the ultrasound sensitive particles and thus causing the release of the material. The ultrasound sensitive particles comprise sub-groups of ultrasound sensitive particles, the ultrasound sensitive particles within the same sub-group having their respective acoustic property causing each respective sub-group to interact independently with the sound wave.