Parallel beamforming using synthetic transmit beams [biomedical ultrasound imaging]

Ultrasound images generated using conventional parallel beamforming contains stationary stripes due to beam-to-beam variations across adjacent beams. Such an imaging system is thus shift variant. This paper investigates a method which eliminates this flaw and restores the shift invariant property. The beam-to-beam variations occur because the transmit and receive beams are not aligned. The underlying idea is then to generate additional synthetic transmit beams (STB) through interpolation of the received, unfocused signal at each array element prior to beamforming. Now each of the parallel receive beams can be aligned perfectly with a transmit beam-synthetic or real-thus eliminating the distortion caused by misalignment. To investigate the performance of the method a simulation study has been conducted. The simulations were done with parameters similar to a standard cardiac examination. Using the proposed method the variation was reduced to 1.5 dB. The simulations were confirmed by results front in vitro experiments where vertical line artifacts were unnoticeable when using the proposed method.