arXiv subjects

Nikunj Khetan

Publications and source records attributed to Nikunj Khetan.

4 recordsLinked to original sources

arXiv2026

Far-field compressive ultrasound beamforming

We present a compressive beamforming method for coherent plane-wave compounding (CPWC) ultrasound imaging based on a far-field decomposition of the received radiofrequency (RF) data into virtual plane waves. This decomposition recasts the imaging operation entirely in the spatial frequency domain ($k$-space), allowing direct and flexible control over $k$-space sampling distributions based on the principle of coarrays. We present vernier-type sampling strategies designed to optimize the tradeoff between image contrast and resolution with minimum redundancy, including strategies that favor dense low-frequency sampling for high contrast, shifted schemes that extend the frequency support for improved resolution, and confocal or hybrid compounding schemes that approximate the spatial-frequency transfer function of conventional DAS beamforming. Our method, called KK beamforming, is validated with a calibration phantom and in-vivo human tissue data, demonstrating compression factors of an order of magnitude while maintaining image qualities comparable to conventional DAS. We further demonstrate that KK beamforming yields improvements in computational speed owing to its reduced memory footprint and more efficient cache utilization of the compressed data and associated look-up tables.

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arXiv2024

Plane-wave compounding with adaptive joint coherence factor weighting

Coherent Plane Wave Compounding (CPWC) is widely used for ultrasound imaging. This technique involves sending plane waves into a sample at different transmit angles and recording the resultant backscattered echo at different receive positions. The time-delayed signals from the different combinations of transmit angles and receive positions are then coherently summed to produce a beamformed image. Various techniques have been developed to characterize the quality of CPWC beamforming based on the measured coherence across the transmit or receive apertures. Here, we propose a more fine-grained approach where the signals from every transmit/receive combination are separately evaluated using a quality metric based on their joint spatio-angular coherence. The signals are then individually weighted according to their measured Joint Coherence Factor (JCF) prior to being coherently summed. To facilitate the comparison of JCF beamforming compared to alternative techniques, we further propose a method of image display standardization based on contrast matching. We show results from tissue-mimicking phantoms and human soft-tissue imaging. Fine-grained JCF weighting is found to improve CPWC image quality compared to alternative approaches.

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arXiv2021

Ultrasound differential phase contrast using backscattering and the memory effect

We describe a simple and fast technique to perform ultrasound differential phase contrast (DPC) imaging in arbitrarily thick scattering media. Though configured in a reflection geometry, DPC is based on transmission imaging and is a direct analogue of optical differential interference contrast (DIC). DPC exploits the memory effect and works in combination with standard pulse-echo imaging, with no additional hardware or data requirements, enabling complementary phase contrast (in the transverse direction) without any need for intensive numerical computation. We experimentally demonstrate the principle of DPC using tissue phantoms with calibrated speed-of-sound inclusions.

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arXiv2020

Speed-of-sound imaging by differential phase contrast with angular compounding

We describe a technique to reveal speed-of-sound (SoS) variations within an echogenic sample. The technique uses the same receive data as standard pulse-echo imaging based on plane-wave compounding, and can be operated in parallel. Point-like scatterers randomly distributed throughout the sample serve as local probes of the downstream transmit-beam phase shifts caused by aberrating structures within the sample. Phase shifts are monitored in a differential manner, providing signatures of transverse gradients of the local sample SoS. The contrast of the signatures is augmented by a method of angular compounding, which provides ``focus" control of the image sharpness, which, in turn, enables a visual localization of aberrating inclusions within the sample on the fly. The localization can be performed in 2D when operated with standard B-mode imaging, or in 3D when operated with C-mode imaging. Finally, we present a wave-acoustic forward model that provides insight into the principle of differential phase contrast (DPC) imaging, and roughly recapitulates experimental results obtained with an elastography phantom. In particular, we demonstrate that our technique easily reveals relative SoS variations as small as 0.5\% in real time. Such imaging may ultimately be useful for clinical diagnosis of pathologies in soft tissue.

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