The fully digital three-dimensional (3D)/(4D:3D+time) ultrasound system technology consists of an advanced beamforming structure that allows the implementation of adaptive and synthetic aperture signal processing techniques in ultrasound systems deploying multidimensional arrays of sensors. Implementation of an adaptive beamformer is a software installation on a PC-based ultrasound computing architecture with sufficient throughput for 3D and 4D ultrasound image processing. Moreover, the PC-based ultrasound computing architecture can accommodate the processing requirements of the "traditional" linear array 2D scans as well as the advanced matrix-arrays performing volumetric scans. The 3D ultrasound imaging systems have three components: image acquisition, reconstruction of the 3D image, and display. There are numerous developments and evaluating techniques for obtaining 3D ultrasound images using the following two approaches: mechanical scanning and freehand scanning. The experimental 3D/4D ultrasound developments demonstrate an imaging technology that can lead to a next generation high-resolution diagnostic ultra-sound imaging systems.