A medical high intensity focused ultrasound system comprising: a base unit including: (a) a primary controller having a primary digital interface; (b) a cooling liquid recirculation circuit; and (c) a cable carrying an electrical transmission member, an information transmission member, and a plurality of cooling liquid conduits; and a therapy head including: (a) a body coupled to the cable; (b) a secondary controller configured to control a transducer and having a secondary digital interface, the secondary controller coupled to said primary controller by the electrical transmission member and the information transmission member; and (c) a cartridge removably attached to the body, the cartridge including a sealed enclosure, acoustic coupling liquid inside the sealed enclosure, and the high intensity focused ultrasound transducer in the acoustic liquid inside the sealed enclosure, the cartridge further including a heat exchanger (614, 750) coupled to the cooling liquid recirculation circuit via the cooling liquid conduits when the cartridge is attached to the body, and the transducer coupled to the electrical transmission member when the cartridge is attached to the body, wherein the acoustic coupling liquid is separated by the heat exchanger (614, 750) from a cooling liquid supplied to the heat exchanger (614, 750) by the cooling liquid conduits. a base unit including: (a) a primary controller having a primary digital interface; (b) a cooling liquid recirculation circuit; and (c) a cable carrying an electrical transmission member, an information transmission member, and a plurality of cooling liquid conduits; and (a) a primary controller having a primary digital interface; (b) a cooling liquid recirculation circuit; and (c) a cable carrying an electrical transmission member, an information transmission member, and a plurality of cooling liquid conduits; and a therapy head including: (a) a body coupled to the cable; (b) a secondary controller configured to control a transducer and having a secondary digital interface, the secondary controller coupled to said primary controller by the electrical transmission member and the information transmission member; and (c) a cartridge removably attached to the body, the cartridge including a sealed enclosure, acoustic coupling liquid inside the sealed enclosure, and the high intensity focused ultrasound transducer in the acoustic liquid inside the sealed enclosure, the cartridge further including a heat exchanger (614, 750) coupled to the cooling liquid recirculation circuit via the cooling liquid conduits when the cartridge is attached to the body, and the transducer coupled to the electrical transmission member when the cartridge is attached to the body, (a) a body coupled to the cable; (b) a secondary controller configured to control a transducer and having a secondary digital interface, the secondary controller coupled to said primary controller by the electrical transmission member and the information transmission member; and (c) a cartridge removably attached to the body, the cartridge including a sealed enclosure, acoustic coupling liquid inside the sealed enclosure, and the high intensity focused ultrasound transducer in the acoustic liquid inside the sealed enclosure, the cartridge further including a heat exchanger (614, 750) coupled to the cooling liquid recirculation circuit via the cooling liquid conduits when the cartridge is attached to the body, and the transducer coupled to the electrical transmission member when the cartridge is attached to the body, wherein the acoustic coupling liquid is separated by the heat exchanger (614, 750) from a cooling liquid supplied to the heat exchanger (614, 750) by the cooling liquid conduits.