Quantitative speed-of-sound (SOS) imaging remains a significant challenge in biomedical photoacoustic (PA) imaging. Existing SOS imaging methods often depend on full-angle measurement, posing limitations for clinical translation. To break through this limitation, this study adopts a linear array-based photoacoustic imaging system and proposes an innovative SOS imaging method by scanning a passive target. We establish a linear model to correlate the measured time-of-flight variations to the SOS distribution in the imaging field. We express the SOS reconstruction problem as a least-squares optimization problem, and use gradient descent to iteratively solve for the SOS map. We verify our method through numerical simulations and phantom experiments and the results prove that it can accurately reconstruct SOS heterogeneities. We also successfully visualize the SOS distribution of ex vivo biological tissue with high consistent on anatomical tissue structure. Our method establishes a promising framework for quantitative SOS mapping by using linear array-based photoacoustic tomography.
Wang et al. (Fri,) studied this question.