A method for detecting the position of a transducer for monitoring the position and motion of one or more target structures for the preparation or during an operation, with creating at least one volume data set (CT or MRI) showing the target structure(s), possible contact surfaces for the positioning of the ultrasonic transducer and the tissue between contact surfaces and target structure(s), determining from the volume data set one or more contact surfaces on which the best reflection of the ultrasound is or are to be expected, and positioning the ultrasonic transducer which monitors the operation on the contact surface(s).
