1. An ultrasound system, comprising: an ultrasound data acquisition unit configured to form a first set of ultrasound frame data and a second set of ultrasound frame data by using non-steered scan lines and steered scan lines, respectively, the steered scan lines being steered at a predetermined steering angle with respect to the non-steered scan lines; and a processor coupled to the ultrasound data acquisition unit and configured to form a plurality of sets of resampled ultrasound frame data based on the second set of ultrasound frame data, select one particular set of ultrasound frame data from the group consisting of the second set of ultrasound frame data and the plurality of sets of resampled ultrasound frame data based on the first set of ultrasound frame data and spatially compound the one particular set of ultrasound frame data and the first set of ultrasound frame data to form an ultrasound spatial compound image.