BB p-DAS, an extension of p-DAS to baseband domain for Doppler imaging

Over the last decade, several beamforming algorithms have been proposed to improve both resolution and contrast of ultrasound imaging over the conventional Delay-And-Sum (DAS), such as adaptive approaches, subspace methods, or nonlinear operators. The latter include p-DAS, which operates only on radio-frequency (RF) signals, and BB p-DMAS, a flexible alternative to either RF or I/Q (in-phase and quadrature) signals (in the baseband domain). BB p-DMAS visually provides the same result as p-DAS on RF but shifts the central frequency of the beamformed signals to $p\times f_{0}$, which can lead to unwanted aliasing in Doppler imaging. In this work, we introduce BB p-DAS, an improved version of p-DAS that operates in the baseband domain and preserves the spectral information centered at $f_{0}$. We formulated it to prove the strict equivalence with BB p-DMAS in terms of B-Mode image characteristics. We highlighted the advantage of keeping the spectrum of the beamformed signal centered at $f_{0}$ with visual examples of color Doppler imaging on a rotating disk.