Recovery of the complete data set from ultrasound sequences with arbitrary transmit delays

Abstract

Ultrasound beamforming relies on particular models of propagation to convert samples of the backscattered field through time into spatial samples of an image. The most common model used is straight-line propagation of a focused wave, assuming a narrow steered and focused beam that propagates radially along a selected direction. This model describes the main propagating pulse but fails to capture the true spatial extent of the wave. The reconstructed image suffers from defocusing, reduced signal-to-noise ratio (SNR), and contrast loss. A method is proposed to model transmission as the superposition of individual transmit elements on the transducer array and to efficiently recover the "complete data set", individual element transmit and receive responses, from an arbitrary scan sequence. Standard diverging wave focusing is applied to the complete data set to produce an image independent of the applied transmit focusing. For a sequence with a fixed transmit focus, the result is a high-SNR, two-way focused image. The proposed method also improves upon other synthetic transmit aperture methods such as plane wave and diverging wave imaging. Phantom and in vivo images are used to demonstrate comparable image quality across different transmit geometries.