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Tomographic reconstruction of the curl and divergence of 2D vector fields taking refractions into account. (English) Zbl 1208.65179

Summary: This article is concerned with the problem of reconstructing the curl and divergence of two-dimensional (2D) vector fields from ultrasound time-of-flight measurements taking the refraction of the emitted ultrasound rays into account. Usually, in 2D vector field tomography the refraction of the ultrasound signal is neglected; i.e., one assumes that the signal propagates along straight lines. We address refractive effects, assuming that the ultrasound signal propagates along the geodesics of a Riemannian metric that is associated with the refractive index which is due to Fermat’s principle. The investigated vector field, however, is still defined on a domain in \(\mathbb{R}^2\) that is equipped with the Euclidean metric. We show a connection between the ray transforms and the Radon transform along geodesic curves which generalizes a well-known result from the Euclidean case. Relying on this relation, we develop an asymptotic reconstruction formula for computing the curl and divergence of the vector field using Fourier integral operators. This article concludes with detailed numerical tests proving on the one hand a good performance of our method and showing on the other hand an improvement compared with computations that assume a propagation along straight lines.

MSC:

65R10 Numerical methods for integral transforms
44A12 Radon transform
65R32 Numerical methods for inverse problems for integral equations
92C55 Biomedical imaging and signal processing
94A12 Signal theory (characterization, reconstruction, filtering, etc.)