Displacement Estimation Methods for Speed-of-Sound Imaging in Pulse-Echo

Speed-of-sound (SoS) is a quantitative imaging biomarker sensitive to structural changes due to pathology, and hence SoS imaging could facilitate differential diagnosis. Ultrasound Computed Tomography (USCT) was proposed to obtain spatially-resolved SoS images based on transmission measurements, but submersed imaging setups are limited to breast applications and involve several practical limitations. Several methods have recently been proposed for reconstructing SoS images using conventional US probes by electronically steering US beam in different directions and exploiting echo time delays between such different viewing angles. For an accurate SoS reconstruction outcome, these methods all inherently rely on accurate time delay estimations (DE) between frames of separately beamformed radio-frequency (RF) data. DE methods for US imaging have been widely studied in elastography. In this work, we study and compare several conventional DE methods for the SoS reconstruction task with numerical and tissue-mimicking phantoms. Since SoS contrast affects max time-delays and potential consequent phase wrapping, we further evaluate SoS contrast dependency of reconstructions.