1. An ultrasound system, comprising: a transmission/reception (Tx/Rx) unit configured to repeatedly transmit/receive an ultrasound beam along scan lines in a target object to output receive signals; an image processing unit configured to form plurality of consecutive ultrasound images based on the receive signals and setting a center of the target object on each of the ultrasound images, the image processing unit being further configured to set radial scan lines in radial directions with respective to the center on each of the ultrasound image and reconstruct the ultrasound images such that the radial scan lines are in parallel with each other to form reconstruction images; and an elastic image forming unit configured to form at least one elastic image based on the reconstruction images.