A focused ultrasound system , comprising: a transducer assembly that includes: a plurality of transmit arrays composed of transmit transducer elements , each transmit array operating at a different frequency; at least one receive array composed of receive transducer elements ; a processor in communication with the transducer assembly and configured to: set a focal region for the transducer assembly; iteratively update the focal region for each transmit array in the transducer assembly by: selecting the transmit array having the lowest remaining operating frequency; directing the selected transmit array to excite the initial focal region for that transmit array; directing the at least one receive array to receive signals from the initial focal region; reconstructing an image of the focal region from the received signals; computing phase correction values from the reconstructed image; characterised in that the processor is configured to apply the computed phase correction values to the selected transmit array and to the transmit array having the next highest operating frequency. a transducer assembly that includes: a plurality of transmit arrays composed of transmit transducer elements , each transmit array operating at a different frequency; at least one receive array composed of receive transducer elements ; a plurality of transmit arrays composed of transmit transducer elements , each transmit array operating at a different frequency; at least one receive array composed of receive transducer elements ; a processor in communication with the transducer assembly and configured to: set a focal region for the transducer assembly; iteratively update the focal region for each transmit array in the transducer assembly by: selecting the transmit array having the lowest remaining operating frequency; directing the selected transmit array to excite the initial focal region for that transmit array; directing the at least one receive array to receive signals from the initial focal region; reconstructing an image of the focal region from the received signals; computing phase correction values from the reconstructed image; characterised in that the processor is configured to apply the computed phase correction values to the selected transmit array and to the transmit array having the next highest operating frequency. set a focal region for the transducer assembly; iteratively update the focal region for each transmit array in the transducer assembly by: selecting the transmit array having the lowest remaining operating frequency; directing the selected transmit array to excite the initial focal region for that transmit array; directing the at least one receive array to receive signals from the initial focal region; reconstructing an image of the focal region from the received signals; computing phase correction values from the reconstructed image; characterised in that the processor is configured to apply the computed phase correction values to the selected transmit array and to the transmit array having the next highest operating frequency. selecting the transmit array having the lowest remaining operating frequency; directing the selected transmit array to excite the initial focal region for that transmit array; directing the at least one receive array to receive signals from the initial focal region; reconstructing an image of the focal region from the received signals; computing phase correction values from the reconstructed image; characterised in that the processor is configured to apply the computed phase correction values to the selected transmit array and to the transmit array having the next highest operating frequency. <EOS>