Elevation focusing by beamformer channel sharing

Abstract

An ultrasound imaging system provides for depth-variable elevational and azimuthal focusing by combining electronic beamforming and fixed mechanical lens (or element shaping). The imaging system includes a plurality of beamformer channels that are selectively allocated to the imaging elements of an array. For phased arrays, a switching circuit controls the allocation of the beamformers, while a linear/convex array also requires an aperture shifting circuit for shifting the aperture along the array. The elevational focusing is achieved using a small number of beamformer channels by sharing the beamformer channels assigned to azimuthal elements for far field imaging and to elevational elements for near field imaging. A portion of the beamformer channels are connected to elevational elements (elements in the off-center rows) during near-field imaging. During far-field imaging, these channels connected to the elevational elements are allocated to the lateral elements for azimuthal focusing, and the elevational elements are allocated directly to the center-row elements of their column. The mechanical focus depth is chosen to be in the far field to provide improved elevation focusing in the far field without the need for electronic beamforming delays. In addition, since the f-number is large in the far field, the depth of focus will be large.