A system operable to deliver ultrasound energy to a patient's brain, the system comprising: an ultrasound transducer assembly comprising: at least one imaging ultrasound transducer; and at least one treatment ultrasound transducer; wherein the at least one imaging transducer and the at least one treatment transducer are arranged to be supported against the head of a person with the at least one imaging ultrasound transducer at a location corresponding to an acoustic window in the person's skull; an ultrasound system connected to operate the at least one imaging ultrasound transducer at a first frequency of operation to generate one or more ultrasound images of structures of the brain and to operate the at least one treatment ultrasound transducer to deliver ultrasound energy to at least one target region within the brain at a second frequency of operation lower than the first frequency of operation; a data store; a data processor configured to: process one of the ultrasound images with a corresponding previously obtained image in the data store to register, based on at least one of the structures in the one or more ultrasound images and the at least one of the structures in the previously obtained image, the previously-obtained image to the ultrasound image to yield a transformation relating coordinates in a frame of reference of the previously obtained image to coordinates in a frame of reference of the ultrasound image; using the transformation, determine coordinates of the at least one target region in the frame of reference of the ultrasound image; and based on the coordinates of the at least one target region, determine at least one target location for the at least one treatment ultrasound transducer to deliver the ultrasound energy to the at least one target region. an ultrasound transducer assembly comprising: at least one imaging ultrasound transducer; and at least one treatment ultrasound transducer; at least one imaging ultrasound transducer; and at least one treatment ultrasound transducer; wherein the at least one imaging transducer and the at least one treatment transducer are arranged to be supported against the head of a person with the at least one imaging ultrasound transducer at a location corresponding to an acoustic window in the person's skull; an ultrasound system connected to operate the at least one imaging ultrasound transducer at a first frequency of operation to generate one or more ultrasound images of structures of the brain and to operate the at least one treatment ultrasound transducer to deliver ultrasound energy to at least one target region within the brain at a second frequency of operation lower than the first frequency of operation; a data store; a data processor configured to: process one of the ultrasound images with a corresponding previously obtained image in the data store to register, based on at least one of the structures in the one or more ultrasound images and the at least one of the structures in the previously obtained image, the previously-obtained image to the ultrasound image to yield a transformation relating coordinates in a frame of reference of the previously obtained image to coordinates in a frame of reference of the ultrasound image; using the transformation, determine coordinates of the at least one target region in the frame of reference of the ultrasound image; and based on the coordinates of the at least one target region, determine at least one target location for the at least one treatment ultrasound transducer to deliver the ultrasound energy to the at least one target region. process one of the ultrasound images with a corresponding previously obtained image in the data store to register, based on at least one of the structures in the one or more ultrasound images and the at least one of the structures in the previously obtained image, the previously-obtained image to the ultrasound image to yield a transformation relating coordinates in a frame of reference of the previously obtained image to coordinates in a frame of reference of the ultrasound image; using the transformation, determine coordinates of the at least one target region in the frame of reference of the ultrasound image; and based on the coordinates of the at least one target region, determine at least one target location for the at least one treatment ultrasound transducer to deliver the ultrasound energy to the at least one target region.