1. A semi-invasive ultrasound imaging system for imaging biological tissue, comprising: a probe including an elongated body with a distal end comprising a two-dimensional ultrasound transducer array; a transmit beamformer connected to said transducer array and constructed to transmit several ultrasound beams over a selected azimuthal range and a selected elevation range of locations; a receive beamformer, connected to said transducer array, constructed to acquire ultrasound data from echoes reflected over a selected tissue volume delineated by said emitted ultrasound beams and a selected sector scan depth and synthesize image data from said acquired ultrasound data; and an image generator constructed to receive said image data and generate at least one image of the selected tissue volume that are displayed on an image display.