Abstract: An ultrasound imaging system (1) comprises a transducer probe (2) for supplying ultrasound waves to a subject area (A), for receiving ultrasound waves reflecting from the subject area (A), and for converting the reflecting waves into a first electrical signal, at least one position sensor (3) provided in the transducer probe (2) for detecting positional information on the transducer probe (2) relative to the subject area (A) during operation, and for generating a second electrical signal corresponding to the detected positional information, a processing unit (41) for controlling the transducer probe (2) and for processing the first and second electrical signals into an image. The position sensor (3) comprises a unit (23) for optically acquiring images of a surface of the subject area (A) during operation, for acquiring information from said images, and for processing said information into positional information on the transducer probe (2) relative to the subject area (A).