sensor coupled to the ultrasound probe provides position information related to an ultrasound imaging position in the object . a processor performs first registration between the medical image and the ultrasound image based on the anatomical feature in the ultrasound image and a medical image of the object acquired by imaging modality different from the ultrasound apparatus , obtains first registration information which provides a relationship between a coordinate system of the medical image and a coordinate system of the ultrasound image based on the first registration , performs second registration between the sensor and the medical image based on the position information and the first registration information , and obtains second registration information based on the second registration . a display may display a portion of the medical image corresponding to the ultrasound imaging position based on the second registration information . the medical image includes one of spect , pet , mr , pet - ct , and pet - mr image .