1. A method of operating an ultrasonic diagnostic apparatus, the method comprising: displaying an ultrasonic image in a first region of a display unit; selecting a region of interest (ROI) in the ultrasonic image; displaying a first scan conversion image and a second scan conversion image in a second region, wherein the first scan conversion image is generated by enlarging or reducing an image corresponding to the selected ROI at a first magnification and the second scan conversion image is generated by enlarging or reducing the image corresponding to the selected ROI at a second magnification; and acquiring a first measurement value of the ROI on the basis of the first scan conversion image, acquiring a second measurement value of the ROI on the basis of the second scan conversion image, and acquiring a third value calculated on the basis of the first and second measurement values, wherein resolution of the scan conversion image is equal to or higher than resolution of the ultrasonic image.