A radiation force balance calibrator (100) for calibrating a high intensity focused ultrasound transducer (106), the radiation force balance calibrator comprising:- a balance frame (130)- a force sensor (138) for measuring force, wherein the force sensor is attached to the balance frame- a balance (124) with first (132) and second ends (134), wherein the first end is attached to a pivot (128) for enabling the balance to pivot relative to the balance frame, wherein the second end is adapted for exerting force onto the force sensor- an oil target phantom (116) connected to the balance for absorbing ultrasound radiation (112, 114) from the high intensity focused ultrasound transducer, wherein the absorption of ultrasonic radiation causes a reduction in the force exerted by the balance on the force sensor andwherein the radiation force balance calibrator is constructed of non-magnetic materials.
