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Focalisation d'ultrasons par retournement temporel et filtre inverse, application à l'échographie transcrânienne

Abstract : Transcranial ultrasound images exhibit a low quality, because of the aberrating effects of the skull bone. It has been shown that using time reversal or inverse filtering it is possible to obtain a good focusing through the skull. The strategy is to emit a distorted wave front that, after further distortion by the skull, restores a good focusing. The calculation of the corrections to apply to the emitted wavefront is based on the measurement of the Green's functions between the transducers of the echographic array and the desired focal points. It is thus necessary to embed a set of transducers in the medium under investigation in order to measure the Green's functions. This is prohibitive for direct applications of these techniques to medical imaging. We show here how to modify the existing adaptive focusing techniques in a non invasive way: non invasive time reversal and inverse filter allow us to obtain transcranial images of better quality. Moreover, the problem we had to solve here: « how to adaptively focus ultrasounds through an aberrating medium without using transducers embedded in the medium » induced us to wonder « how can we guess the effect of the propagating medium on transmitted waves, from information carried by the reflected waves (that can be measured non invasively) ? » This allowed us to highlight the link that exists between time reversal and inverse filter, via the Stokes equations. We also drew the basis of a new technique to obtain a minimally invasive inverse filter, opening interesting perspectives in telecommunications.
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https://tel.archives-ouvertes.fr/tel-00010706
Contributor : Francois Vignon <>
Submitted on : Thursday, October 20, 2005 - 10:12:45 PM
Last modification on : Wednesday, October 14, 2020 - 4:07:47 AM
Long-term archiving on: : Friday, September 14, 2012 - 3:10:09 PM

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  • HAL Id : tel-00010706, version 1

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Francois Vignon. Focalisation d'ultrasons par retournement temporel et filtre inverse, application à l'échographie transcrânienne. Traitement du signal et de l'image [eess.SP]. Université Paris-Diderot - Paris VII, 2005. Français. ⟨tel-00010706⟩

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