Dual-Probe Pulse-Echo Speed-of-Sound Imaging

Knowledge of the spatial distribution of speed of sound (SoS) will greatly improve the diagnostic power of abdominal ultrasound (US) imaging. It can be used to account for wavefront aberrations and improving the B-mode image quality, but SoS is also an important disease marker as it can reflect disease-related changes in tissue composition. However, the relatively small aperture size compared to the desired image depth in abdominal US imaging inherently limits the axial resolution and the estimation accuracy of determining SoS. Fundamentally, a larger physical aperture would produce images with improved contrast and resolution. In this study, we assess the impact of combining two probes to a larger aperture on the estimation accuracy of SoS. Two ways of dual-probe operation are investigated, monostatic (where only one probe transmits and receives at a time) and bistatic (where both probes receive on each transmit), as well as classical single probe operation. The quality of SoS maps is compared in digital and physical phantoms mimicking abdominal imaging. The primary result is that axial resolution of bistatic operation clearly outperforms the one of monostatic dual-probe operation, both in simulations (by 74% and 96%) and in the experiment (by 103%), indicating that the larger angle differences provided by trans-aperture data (where one probe receives and the other transmits) is essential for the superior axial resolution. Furthermore, bistatic dual-probe operation produced SoS maps with improved background uniformity and performed best at recovering layer contrast, while the latter was substantially more underestimated in monostatic dual-probe and classical single probe operation. This study emphasizes the importance of larger effective apertures for future ultrasound device designs.