Cartridge apparatus (230) for use with a handle (220) is provided. The apparatus includes a housing (500) which: (a) includes a handle-coupling portion (235) shaped and sized to securely couple the housing to the handle and to facilitate separation of the housing from the handle, (b) shaped to define a skin-application portion (40) on an outer surface of the housing, and (c) includes at least one ultrasound element (60) in acoustic communication with the skin-application portion and configured to transmit ultrasound energy to the skin through the skin-application portion when the cartridge is attached to the handle. The cartridge apparatus also includes an inflatable element (250) inflated with a fluid, the fluid being in fluid communication with the skin-application portion. Other applications are also described.
