Speed-of-sound imaging using diverging waves

Abstract

Purpose. Due to its safe, low-cost, portable, and real-time nature, ultrasound is a prominent imaging method in computer-assisted interventions. However, typical B-mode ultrasound images have limited contrast and tissue differentiation capability for several clinical applications. Methods. Recent introduction of imaging speed-of-sound (SoS) in soft tissues using conventional ultrasound systems and transducers has great potential in clinical translation providing additional imaging contrast, e.g., in intervention planning, navigation, and guidance applications. However, current pulse-echo SoS imaging methods relying on plane wave (PW) sequences are highly prone to aberration effects, therefore suboptimal in image quality. In this paper we propose using diverging waves (DW) for SoS imaging and study this comparatively to PW. Results. We demonstrate wavefront aberration and its effects on the key step of displacement tracking in the SoS reconstruction pipeline, comparatively between PW and DW on a synthetic example. We then present the parameterization sensitivity of both approaches on a set of simulated phantoms. Analyzing SoS imaging performance comparatively indicates that using DW instead of PW, the reconstruction accuracy improves by over 20% in root-mean-square-error (RMSE) and by 42% in contrast-to-noise ratio (CNR). We then demonstrate SoS reconstructions with actual US acquisitions of a breast phantom. With our proposed DW, CNR for a high contrast tumor-representative inclusion is improved by 42%, while for a low contrast cyst-representative inclusion a 2.8-fold improvement is achieved. Conclusion. SoS imaging, so far only studied using a plane wave transmission scheme, can be made more reliable and accurate using DW. The high imaging contrast of DW-based SoS imaging will thus facilitate the clinical translation of the method and utilization in computer-assisted interventions such as ultrasound-guided biopsies, where B-Mode contrast is often to low to detect potential lesions.

Phase-Aberration Correction in Shear-Wave Elastography Imaging Using Local Speed-of-Sound Adaptive Beamforming

“…Since soft tissues are intrinsically inhomogeneous, for accurate tissue characterization and diagnosis using SWEI, it appears imperative given our study to beamform MA-PWI data using accurate SoS distributions of the medium to alleviate possible confounding effects of SoS and beamforming on estimated SWS. For estimating such local SoS distributions, one could use the same ultrasound transducer used for SWEI as in [16]; [17]; [18] as demonstrated for aberration correction in [19].…”

“…Several groups showed SoS reconstruction for submersible body parts using ring or rotating transducer setups. To alleviate the need for complex setups, hand-held solutions with acoustic reflector based, e.g., [15]; [31], and pulse-echo disparity based, e.g., [17]; [18], tomographic reconstruction methods were also demonstrated. To achieve fast, real-time SoS map estimations, such reconstructions have also been accelerated using deep-learning based techniques in [32] and [33].…”

“…So it is naturally beneficial to develop SoS imaging to be compatible with existing conventional ultrasound transducers in order to avail several logistic advantages of commercial transducer arrays, also for SoS imaging in the clinics. Time-of-flight recordings together with a passive acoustic reflector [14]; [15] or minute misalignments between images viewed from different angles [16]; [17]; [18] were used for tomographic reconstruction of SoS. Given SoS maps, delays to any spatial location can also be calculated to correct for aberrations caused by SoS inhomogeneities; these delays can be used for beamforming, called SoS-adaptive beamforming, which was shown to increase the resolution of B-mode imaging [19].…”

Frequency-Dependent Attenuation Reconstruction with an Acoustic Reflector

“…Due to the ill-conditioning of L, a regularization term controlled by weight λ encourages spatial smoothness. Similarly to [26,27,30,33], we herein use 1 -norm for both the data and regularization terms for robustness to outliers in, respectively, the measurements and the reconstructed image (edges) [15]. Due to a lack of full angular coverage of measurements, regularization matrix D implements LA-CT specific image filtering to suppress streaking artifacts orthogonal to missing projections via anisotropic weighting of directional gradients [30].…”

“…in transmission utilizing custom made transducer architectures [12,22] and in pulse-echo using conventional ultrasound scanners. For the latter, the setups can be divided into two subgroups: 1) Based on methods that measure apparent displacements of backscattered signals insonified from different angles [32,27,26] and 2) based on methods that use an additional passive acoustic reflector to record corresponding time-of-flight values [30,30]. A quantification of in-vivo speed-of-sound imaging was recently proposed for breast density [31] and sarcopenia assessment [29].…”