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A new synthetic aperture focusing method using nonspherical wave fronts

Conventional ultrasound focusing techniques suffer from poor lateral resolution due to the diffraction spreading of ultrasound waves. In this paper, we present a new two-way dynamic focusing method with limited diffraction properties. Specifically, the new method is a synthetic aperture focusing (SAF) method utilizing linear wave fronts for synthetic transmit focusing, instead of spherical wave fronts, to reduce the diffraction spreading effect. In the proposed method, data acquisition and beamforming are performed in the same manner as in other known SAF methods. The main difference is that for each firing all array elements are used to transmit a plane wave of which the traveling angle varies with the receive subaperture position. On receiving, each scan line is formed by synthesizing the relevant receive subaperture fields with delays to force the plane waves to meet at each imaging point. In this paper, the properties of the proposed scheme are theoretically analyzed with a hypothetical infinite line source that is used to transmit the plane waves. It is verified by computer simulation that the proposed scheme can be realized with a finite aperture and the resultant lateral beam pattern has smaller mainlobe widths than those of conventionally focused two-way beam pattern at all depths.