A therapeutic apparatus comprising: - a high intensity focused ultrasound system adapted for sonicating a sonication volume of a subject; - a magnetic resonance imaging system adapted for acquiring magnetic resonance thermometry data from nuclei of the subject located within an imaging volume, wherein the sonication volume is within the imaging volume; and - a controller adapted for controlling the therapeutic apparatus, wherein the controller is adapted for receiving a treatment plan specifying a target volume within the imaging volume, wherein the treatment plan comprises instructions for controlling the operation of the high intensity focused ultrasound system, wherein the controller is adapted for sonicating the target volume using the high intensity focused ultrasound system by executing the treatment plan, wherein the controller is adapted for repeatedly acquiring magnetic resonance thermometry data using the magnetic resonance imaging system during execution of the treatment plan, and wherein the controller is adapted for modifying the treatment plan during execution of the treatment plan using the magnetic resonance thermometry data; wherein the controller is a computing device comprising a processor; wherein the therapeutic apparatus further comprises a computer-readable storage medium containing instructions for execution by the processor, wherein execution of the instructions causes the processor to control the therapeutic apparatus to perform a method of sonicating a target volume; wherein the method comprises the steps of: - receiving the treatment plan specifying the target volume within the imaging volume; - acquiring magnetic resonance image data using the magnetic resonance imaging system; - registering the magnetic resonance image data to the treatment plan; - modifying the treatment plan using the registration of the magnetic resonance image data to the treatment plan; - controlling the high intensity focused ultrasound system by executing the treatment plan; - acquiring magnetic resonance thermometry data repeatedly during execution of the treatment plan; and - modifying the treatment plan using the repeatedly acquired magnetic resonance thermometry data; wherein the method further comprises updating the magnetic resonance imaging data repeatedly during execution of the treatment plan, wherein the method further comprises modifying the treatment plan using the repeatedly updated magnetic resonance imaging data; and characterised in that the step of modifying the treatment plan using the repeatedly updated magnetic resonance image data comprises modeling the transmission of ultrasound from a high intensity focused ultrasound transducer of the high intensity focused ultrasound system to the target volume using the repeatedly updated magnetic resonance imaging data. - a high intensity focused ultrasound system adapted for sonicating a sonication volume of a subject; - a magnetic resonance imaging system adapted for acquiring magnetic resonance thermometry data from nuclei of the subject located within an imaging volume, wherein the sonication volume is within the imaging volume; and - a controller adapted for controlling the therapeutic apparatus, wherein the controller is adapted for receiving a treatment plan specifying a target volume within the imaging volume, wherein the treatment plan comprises instructions for controlling the operation of the high intensity focused ultrasound system, wherein the controller is adapted for sonicating the target volume using the high intensity focused ultrasound system by executing the treatment plan, wherein the controller is adapted for repeatedly acquiring magnetic resonance thermometry data using the magnetic resonance imaging system during execution of the treatment plan, and wherein the controller is adapted for modifying the treatment plan during execution of the treatment plan using the magnetic resonance thermometry data; - receiving the treatment plan specifying the target volume within the imaging volume; - acquiring magnetic resonance image data using the magnetic resonance imaging system; - registering the magnetic resonance image data to the treatment plan; - modifying the treatment plan using the registration of the magnetic resonance image data to the treatment plan; - controlling the high intensity focused ultrasound system by executing the treatment plan; - acquiring magnetic resonance thermometry data repeatedly during execution of the treatment plan; and - modifying the treatment plan using the repeatedly acquired magnetic resonance thermometry data;