Abstract: An adaptive multidimensional beamformer having near-instantaneous convergence for ultrasound imaging systems deploying multidimensional sensor arrays is disclosed. In a first step, the multidimensional beamformer is decomposed into sub-apertures. Each sub-aperture is then again decomposed into two coherent subsets of circular and/or line array beamformers in different coordinate directions of the multidimensional array. Implementation of the multidimensional beamformer according to the present invention provides the basis for a 3D ultrasound imaging system according to the present invention comprising a compact multidimensional sensor array and a compact processing unit that is field deployable and generates high resolution three-dimensional images in real time. It is also possible to capture four-dimensional images, the fourth dimension being time and the resulting images forming a video image of a volume of a moving organ.