1. A three-dimensional (3D) ultrasound imaging system for forming a 3D image, comprising: a display device; at least one transducer, for transmitting ultrasound signals toward an object and receiving echo signals from a voxel corresponding to a pixel on said display device, wherein said voxel is on a scanning region of said object; signal storing means for storing signals from said at least one transducer; signal processing means for processing said stored signals to obtain 3D data sets with respect to said voxel; and image forming means for forming a 3D image based on said 3D data sets.