Frequency Domain Beamforming in Acoustical Radiation Force Impulse Imaging




Konda, Sai Prakash Reddy

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Acoustical radiation force impulse (ARFI) imaging involves inducing and monitoring a tissue deformation response using an ultrasound transducer. At some location of interest, a typical ARFI sequence consists of three pulse types: 1) a reference pulse, used to establish a baseline position of the tissue before the excitation; 2) a pushing pulse, used to generate an acoustical radiation force to induce localized deformation; and 3) tracking pulses, applied immediately following the pushing pulse and used to monitor the tissue displacements over time. Applying such sequences of reference, pushing and tracking pulses can be used to generate 2D elastograms, i.e., images that characterize tissue stiffness, obtained by post-processing of the beamformed ARFI data. In this work, we focus on the beamforming step, where we replace the conventional Delay-and-Sum (DAS) beamformer with a faster alternative called Frequency-Domain Migration (FDM). We also consider the low-cost data acquisition scenario (prior to beamforming), where the raw ARFI data is sampled at 1/2 rate, which is then followed by data interpolation using the Discrete Cosine Transform (DCT) to obtain the full-sized input expected by the FDM method. We use the above mentioned three methods (DAS, FDM, and DCT+FDM) to obtain the three versions of their respective beamformed ARFI data, each giving rise to the corresponding B-mode, displacement, and elastographic images. To generate the latter, we have utilized the time-to-peak (TTP) estimation approach (based on linear regression) to determine shear-wave speed profiles of interest, followed by applying an averaging disc filter. In our evaluations, we have used the public-domain experimental dataset that consists of four groups, or super frames (one per push), each containing 50 plane-wave tracking frames. Our results, based on ARFI imaging of a 10-mm 80-KPa sphere embedded in the 25-KPa background, show that the FDM and DCT+FDM methods are a viable alternative to the conventional and more expensive DAS method.



Frequency Domain Beamforming, Acoustical Radiation Force Impulse Imaging