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Détection et traitement de signaux RMN en champ inhomogène

Abstract : Nuclear Magnetic Resonance (NMR) experiments are commonly done in highly homogeneous magnetic fields. However, portable systems appeared few year ago. Such systems are used for relaxometry experiments, and should be used for spectrometry if the radiofrequency and the static magnetic field are correlated.

In inhomogeneous magnetic fields, the sample must be excited by wideband pulse sequences. Excitation sequences for portable applications have been studied. Chirp pulses may be employed to reduce the RF power. A modelisation of nutation echo signal is useful to evaluate the effect of miscorrelation errors. If the resonance frequency is not well known (this may occurs if the magnet polarization is temperature dependent), the signal-to-noise ratio of the receiver may be increased by a time-frequency representation of the echo signal.

A magnetic system, which creates two correlated and perpendicular magnetic fields, has been designed. This system is based on the easy axis rotation theorem. The influence of end effects and imperfections has been studied. A portable probe has been constructed; the probe measures 8x3x1.5 cm3. Preliminary NMR signals have been obtained with this probe.

A NMR spectrometer has been modified for portable NMR applications. Low noise preamplifiers have been constructed and a control software has been developed. NMR signals have been obtained in inhomogeneous magnetic fields with this spectrometer.
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Contributor : Gaël Le Bec <>
Submitted on : Tuesday, October 9, 2007 - 11:02:55 AM
Last modification on : Thursday, November 19, 2020 - 1:00:26 PM
Long-term archiving on: : Friday, April 9, 2010 - 4:53:04 PM

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Gaël Le Bec. Détection et traitement de signaux RMN en champ inhomogène. Traitement du signal et de l'image [eess.SP]. Université Joseph-Fourier - Grenoble I, 2007. Français. ⟨tel-00177759⟩

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