1. An ultrasound system, comprising: an ultrasound data acquisition unit configured to transmit and receive ultrasound signals to and from a target object to thereby acquire ultrasound data corresponding to a plurality of frames; a volume data forming unit configured to form volume data corresponding to the plurality of frames based on the ultrasound data, the volume data including a plurality of voxels; and a processing unit configured to detect edges of a region of interest (ROI) of the target object from the volume data and perform surface rendering upon voxels within the detected edges to thereby form a 3-dimensional ultrasound image.