Evaluation of Green's functions in complex media by decomposition of the Time Reversal Operator: Application to Medical Imaging and aberration correction

Abstract : The objective of this thesis is to adapt a Time Reversal based method, the DORT method, to medical imaging. Most of the results are valid in other area of applications. The use of Medical ultrasound is limited with certain patients because of the inhomogeneity of tissues. The focusing and therefore the image quality can be severely degraded by the propagation through inhomogeneous media. To correct this problem, and achieve a good focusing, it is required to estimate Green's functions of points in the medium.
We propose an approach using Time Reversal. We extend the theory of the DORT method to the focused acquisition mode, and we introduce the virtual transducer model that simplifies the problem. Then we generalize the method to random signals (speckle) that are the main signals in medical ultrasound. We propose a statistic interpretation based on the Van Cittert Zernike theorem. We are also dealing with extended objects. Finally, in medical ultrasound, large band signals are used, whereas the DORT method is a monochromatic method. A few methods to obtain the time-domain Green's functions are developped. In particular we present the decomposition of the time reversal operator in the time domain, which involves a 4th order tensor.
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Submitted on : Wednesday, September 24, 2008 - 9:13:43 PM
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  • HAL Id : tel-00324395, version 1

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Jean-Luc Robert. Evaluation of Green's functions in complex media by decomposition of the Time Reversal Operator: Application to Medical Imaging and aberration correction. Acoustics [physics.class-ph]. Université Paris-Diderot - Paris VII, 2007. English. ⟨tel-00324395⟩

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