1. A three-dimensional ultrasound system for use with an ultrasound probe connected to a clinical ultrasound machine and a computer for storing a succession of two-dimensional images generated by said clinical ultrasound machine represented by an array of pixels I(x,y,z), responsive to movement of said probe, the system comprising: a) an assembly for mounting said probe adjacent an organ to be examined and for moving said assembly such that said probe scans said organ to be examined in a single sweep, thereby resulting in generation of said succession of two-dimensional images by said clinical ultrasound machine and storage in said computer of said images represented by said array of pixels I(x,y,z); and b) controller means in said computer for (i) controlling movement of said assembly such that said probe sweeps out a predetermined volume of said organ to be examined and (ii) reconstructing said two-dimensional images represented by said array of pixels I(x,y,z) to form a reconstructed three-dimensional image represented by an array of output pixels V(x,y,z).