1. An ultrasound system, comprising: a transmission/reception (Tx/Rx) unit configured to repeatedly transmit/receive an ultrasound beam along first scan lines and the second scan lines in a target object to output first receive signals and second receive signals, respectively, wherein the first scan lines are parallel with each other and the second scan lines are passing a center of the target object; an image processing unit configured to form first ultrasound images and second ultrasound images based on the first receive signals and the second receive signals, respectively, detect boundaries of the target object on each of the first ultrasound images and the second ultrasound images, and set the center of the target object on each of the first ultrasound images and the second ultrasound images based on the detected boundaries, the image processing unit being further configured to set first radial lines in first radial directions with respect to the center on each of the first ultrasound images, set second radial lines in second radial directions with respect to the center on each of the second ultrasound images, and reconstruct the first ultrasound images and the second ultrasound images such that the first radial lines and the second radial lines are in parallel with each other to form first reconstruction images and second reconstruction images, respectively; an image compounding unit configured to form compound images by using the first reconstruction images and the second reconstruction images; and an elastic image forming unit configured to form at least one elastic image based on the compound images.