Present 1D phased array probes have outstanding lateral and axial resolution, but their elevation performance is determined by a fixed aperture focused at a fixed range. Multi-row array transducers can provide significantly improved elevation performance in return for "modest" increases in probe and system complexity. Time domain simulations of elevation beam profiles are used to compare several types of multi-row probes. The elevation aperture of a 1.25D probe increases with range, but the elevation focusing of that aperture is static and determined principally by a mechanical lens with a fixed focus (or foci). 1.25D probes can provide substantially better near- and far-field slice thickness performance than 1D probes and require no additional system beamformer channels. 1.5D, probes use additional beamformer channels to provide dynamic focusing and apodization in elevation. 1.5D probes can provide detail resolution comparable to, and contrast resolution substantially better than, 1.25D probes, particularly in the mid- and far-field. Further increases in system channel count allow the use of 1.75D and 2D arrays for adaptive acoustics and two-dimensional beam steering. Significant improvements in clinical image quality can be expected as multi-row probes become increasingly available in the marketplace.
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