1. An imaging system comprising: a transducer array having a multiplicity of transducer elements for transmitting wave energy in response to electrical activation and transducing returned wave energy into electrical signals; a transmitter coupled to said transducer array and programmed to activate a plurality of said transducer elements to transmit focused wave energy for each of a multiplicity of transmit focal positions in each of a multiplicity of scan planes; a receiver programmed to form receive signals from electrical signals supplied from said plurality of transducer elements subsequent to each transmit for each of a multiplicity of scan lines in each scan plane; a processing subsystem for converting said receive signals into imaging signals for each scan line in each scan plane; memory for storing a respective set of imaging signals for each scan plane to form a data volume; a computer programmed to perform an algorithm for generating projected image data representing a projection of said data volume onto an imaging plane, wherein said algorithm comprises the steps of: (a) generating reformatted slices of pixel data through said data volume, said reformatted slices being mutually parallel; and (b) for each of a multiplicity of rays cast from respective pixels on said imaging plane, calculating a respective accumulated intensity for pixels in said reformatted slices which are substantially registered with said respective cast rays to form said projected image data; and a subsystem for displaying a projected image which is a function of said projected image data.