Real-Time Universal Synthetic Transmit Aperture Beamforming with Retrospective Encoding for Conventional Ultrasound Sequences (REFoCUS)

Retrospective transmit beamforming can be achieved by modeling a set of steered focused, diverging, or plane wave transmissions as virtual sources. These virtual sources are time-delayed and apodized so as to form a synthetic transmit aperture (STA) with dynamic focusing in retrospect. However, a separate time-delay algorithm and geometric model is needed for each case, and the virtual source model limits the granularity with which delays and apodizations can be applied. Multistatic STA has fine granularity due to the use of single element transmits, but suffers from poor electronic signal-to-noise ratio (SNR). Retrospective encoding for conventional ultrasound sequences (REFoCUS) has recently been proposed as a technique to recover the multistatic dataset from ordinary ultrasound sequences with high SNR. REFoCUS treats all transmit sequences as multiplicative frequency-domain encodings that can be (pseudo-)inverted to recover multistatic data. Here, we demonstrate a prototype imaging system capable of real-time frame rates using GPU-based processing.