Theoretical simulations of the pulse-echo beam forming of two-dimensional (2D) circular planar phase-array ultrasound transducers were conducted for the optimization of the effective architectures. These results were compared with equivalent linearly reticulated 2D phase-array transducer configurations. It is predicted that ultrasound imagers based on circular 2D phase-array transducers will outperform the other architectures for several medical applications. This study was motivated by the recent demonstration of micromachining of high-density circular as well as linear reticulated 2D phase-array transducers, to achieve real-time high-resolution completely electronic steerable volumetric medical noninvasive ultrasound imaging.