An ultrasound imaging apparatus includes an ultrasonic probe configured to transmit an ultrasound to an object, receive an echo signal reflected from the object, and output the echo signal; a quality determiner configured to receive the echo signals and determine quality of voxels of a three-dimensional (3D) volume of the object to be rendered based on observation information of the 3D volume; and a beamformer configured to perform beamforming on the echo signal based on the quality of the voxels to generate an output signal.