Exemplary embodiments provide systems and methods for portable medical ultrasound imaging. Preferred embodiments utilize a tablet touchscreen display operative to control imaging and display operations without the need for using traditional keyboards or controls. Certain embodiments provide ultrasound imaging system in which the scan head includes a beamformer circuit that performs far field sub-array beamforming or includes a sparse array selecting circuit that actuates selected elements. Exemplary embodiments also provide an ultrasound engine circuit board including one or more multi-chip modules, and a portable medical ultrasound imaging system including an ultrasound engine circuit board with one or more multi-chip modules. Exemplary embodiments also provide methods for using a hierarchical two-stage or three-stage beamforming system, three dimensional ultrasound images which can be generated in real-time.