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Traitement numérique des signaux et identification de systèmes RMN ; Conception et développement d'un imageur pour l'IRM dédiée à bas champ

Abstract : In the first part of this work, a new complete home-built digital MRI system is developed to enhance the signal-to-noise ratio (SNR) of the NMR signals at low magnetic field. The system is based on a digital signal processor (DSP) which offers high flexibility and accuracy in signal processing and image reconstruction. The key feature of the system is the use of a digital frequency synthesizer and a digital RF receiver. This digital solution enables small size and low cost dedicated MRI instrument which is suitable for use in medical cabinets. Such an instrument is also useful for quality control of agricultural and food products. It is shown that a SNR enhancement of about 20dB, with respect to conventional MRI systems, is achieved. The performances of the new instrument is demonstrated by the first images obtained with the gradient-echo sequence. We report, in the second part, a new approach for NMR systems identification. The approach, based on adaptive filtering techniques, aims to take into account the nonlinear characteristics of NMR systems for more accurate signal processing and analysis. Two models of non linearity are thus introduced and compared. It is provedthat the volterra representation is not the adequate model since a large number of coefficients is necessary to describe the non linear behavior of the NMR system. The nonlinear infinite impulse response (IIR) filter which involves fewer coefficients can represent an alternative model.
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Submitted on : Wednesday, April 14, 2010 - 4:38:36 PM
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  • HAL Id : tel-00473212, version 1

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Aktham Asfour. Traitement numérique des signaux et identification de systèmes RMN ; Conception et développement d'un imageur pour l'IRM dédiée à bas champ. Sciences de l'ingénieur [physics]. Université Joseph-Fourier - Grenoble I, 2002. Français. ⟨tel-00473212⟩

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