Travel-Time Tomography for Local Sound Speed Reconstruction Using Average Sound Speeds

Our previous work on estimating the local speed of sound from average sound speed assumes a perfectly layered medium where sound speed is only allowed to vary axially away from the transducer surface. This layered-medium approach relies on inverting the relationship between the local interval sound speeds in each layer and the effective average sound speed up to a particular imaging depth. The primary limitation of this approach is that local sound speed estimation can become inaccurate in the presence of lateral variations in sound speed or a curved transducer surface. To better estimate sound speed in the presence of these non-idealities, we propose a travel-time tomographic approach that accounts for propagation paths from the scattering volume to each transducer element.