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Proceedings Paper

Robust ultrasound travel-time tomography using the bent ray model
Author(s): Ali Hormati; Ivana Jovanović; Olivier Roy; Martin Vetterli
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Paper Abstract

We present a bent ray reconstruction algorithm for an ultrasound tomography (UT) scanner designed for breast screening. The scanner consists of a circular array of transmitters and receivers which encloses the object to be imaged. By solving a nonlinear system of equations, the reconstruction algorithm estimates the sound speed of the object using the set of travel-time measurements. The main difficulty in this inverse problem is to ensure the convergence and robustness to noise. In this paper, we propose a gradient method to find a solution for which the corresponding travel-times are closest to the measured travel-times in the least squares sense. To this end, first the gradient of the cost function is derived using Fermat's Principle. Then, the iterative nonlinear conjugate gradient algorithm solves the minimization problem. This is combined with the backtracking line search method to efficiently find the step size in each iteration. This approach is guaranteed to converge to a local minimum of the cost function where the convergence point depends on the initial guess. Moreover, the method has the potential to easily incorporate regularity constraints such as sparsity as a priori information on the model. The method is tested both numerically and using in vivo data obtained from a UT scanner. The results confirm the stability and robustness of our approach for breast screening applications.

Paper Details

Date Published: 12 March 2010
PDF: 12 pages
Proc. SPIE 7629, Medical Imaging 2010: Ultrasonic Imaging, Tomography, and Therapy, 76290I (12 March 2010); doi: 10.1117/12.844693
Show Author Affiliations
Ali Hormati, Ecole Polytechnique Fédérale de Lausanne (Switzerland)
Ivana Jovanović, Ecole Polytechnique Fédérale de Lausanne (Switzerland)
Olivier Roy, Ecole Polytechnique Fédérale de Lausanne (Switzerland)
Martin Vetterli, Ecole Polytechnique Fédérale de Lausanne (Switzerland)

Published in SPIE Proceedings Vol. 7629:
Medical Imaging 2010: Ultrasonic Imaging, Tomography, and Therapy
Jan D'hooge; Stephen A. McAleavey, Editor(s)

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