Speed-of-Sound Imaging Based on Reflector Delineation

Abstract

Speed-of-sound (SoS) has large potential for tissue and pathology differentiation. We aim to develop a novel Ultrasound Computed Tomography (USCT) technique that can reconstruct local SoS in tissue on conventional ultrasound machines with hand-held linear arrays. Methods: A passive reflector is placed opposite the tissue sample as an echogenic reference to measure the time-of-flight (ToF) of ultrasound wavefronts. A Dynamic Programming algorithm provides a robust ToF measurements based on global optimization of all transmit-receive echo data. An Anisotropically-Weighted Total Variation (AWTV) algorithm allows sharp delineation of focal lesions based on limited-angle USCT data. Results: Inclusions, which are not visible in conventional ultrasound, could be delineated in SoS images. AWTV allows to reconstruct focal lesions with a contrast-ratio of 93.7% of their nominal value, compared to that of 31.5% with conventional least-squares based algebraic tomographic reconstruction. In fullwave simulations of realistic heterogeneous breast models, a high CR of 84.3% is observed, with the reconstruction filtering out background heterogeneity. In experiments, our proposed method quantifies SoS in a homogeneous background with an accuracy of 0.93 m s −1 , allowing to differentiate several tissue types. Conclusion: We validate our method using numerical simulations with ray-tracing and full-wave models, and phantom and ex-vivo data. Preliminary in-vivo results show the potential of this new technique to detect and differentiate malignant and benign lesions in the breast. Significance: Breast cancer is the most common cancer in women. Ultrasound B-mode only provides qualitative information about breast lesions, whereas USCT can provide quantitative tissue imaging biomarkers, such as SoS. The proposed method can potentially be implemented as a complementary modality to ultrasound for tissue and disease differentiation.

Breast Density Assessment in Young Women with Ultrasound based on Speed of Sound: Influence of the Menstrual Cycle

“…Recently, a novel US method, 2D Speed-of-Sound Ultrasound (SoS-US), has been proposed to measure breast density, which can be implemented as an add-on to standard ultrasound systems. [12,13] This method uses a passive reflector opposite to the breast at a known distance to measure the echo arrival time between a conventional US probe and said reflector. This provides a SoS profile (m/s) along the probe width.…”

“…Breast density classification based on SoS-US has demonstrated a strong correlation to ACR density categories. [12,13] In contrast to 3D-US-tomography, the reflector technique can be quickly performed without a water bath. A modality like SoS-US would also be adequate to non-invasively monitor SoS changes during the menstruation cycle and as a result of hormonal treatment or medication.…”

A Combined Regularization Method Using Prior Structural Information for Sound-Speed Image Reconstruction of Ultrasound Computed Tomography

“…USCT can automatically and non-invasively obtain 3D breast images in three different modalities, namely echo image, sound speed image (SSI), and attenuation image. The USCT imaging system can be built based on conventional linear transducer array [10][11][12][13][14][15][16] or the ring transducer array [17][18]. In this study, the system is based on the ring transducer array, which generally includes a table with an opening on it, a water tank under the opening of the table, and a ring transducer array immersed in the water tank.…”

Ultrasound Aberration Correction based on Local Speed-of-Sound Map Estimation

“…In the recent years, several methods have been proposed that allow for the estimation and 2D mapping of local SoS distribution with conventional US systems, e.g. by time-offlight recordings together with a passive acoustic reflector [5] or from minute misalignments between images acquired at different plane-wave angles [6], [7]. In this paper we propose to utilize such 2D spatial SoS distribution estimates for correcting the delays used in US beamforming ( Fig.…”