Hand-Held Sound-Speed Imaging Based on Ultrasound Reflector Delineation
A novel hand-held speed-of-sound (SoS) imaging method is proposed, which requires only minor hardware extensions to conventional ultrasound (US) B-mode systems. A hand-held reflector is used as a timing reference for US signals. A robust reflector-detection algorithm, based on dynamic programming (DP), achieves unambiguous timing even with 10 dB signal-to-noise ratio in real tissues, successfully detecting delays <100 ns introduced by SoS heterogeneities. An Anisotropically-Weighted Total-Variation (AWTV) regularization based on L1-norm smoothness reconstruction is shown to achieve significant improvements in the delineation of focal lesions. The Contrast-to-noise-ratio (CNR) is improved from 15 dB to 37 dB, and the axial resolution loss from >300 % to <15 %. Experiments with breast-mimicking phantoms and ex-vivo liver samples showed, for hard hypoechogenic inclusions not visible in B-mode US, a high SoS contrast (2.6 %) with respect to cystic inclusions (0.9 %) and the background SoS noise (0.6 %). We also tested our method on a healthy volunteer in a preliminary in-vivo test. The proposed technique demonstrates potential for low-cost and non-ionizing screening, as well as for diagnostics in daily clinical routine.