1. A medical imaging apparatus comprising: an ultrasound apparatus including an ultrasound probe configured to transmit and receive an ultrasound signal to obtain an ultrasound image of an object; a sensor coupled to the ultrasound probe and configured to provide a position information related to an ultrasound imaging position in the object; and a processor configured to extract a certain anatomical feature from the ultrasound image and the certain anatomical feature from a medical image of the object acquired by an imaging modality different from the ultrasound apparatus, perform a first registration between the medical image and the ultrasound image based on the certain anatomical feature, obtain a 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, perform a second registration between the sensor and the medical image based on the position information and the first registration information, obtain a second registration information based on the second registration, and control a display to display a portion of the medical image, corresponding to the ultrasound imaging position based on the second registration information, wherein the medical image comprises one of a single-photon emission computed tomography (SPECT) image, a positron emission tomography (PET) image, a magnetic resonance (MR) image, a PET-computed tomography (CT) image, and a PET-MR image.