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Suites Régulières d'Impulsions Radio-Fréquence en Résonance Magnétique. Application à l'IRM.

Abstract : Regular RF pulse trains used in NMR can be studied with simple algorithms of polynomial type using the Z transform. Another simplification is brought by the use of spinors to model the rotations. The first application presented is a ‘peel-off' algorithm which permits the synthesis of selective radiofrequency pulses as the ones used in MRI. This algorithm makes the non linearity of the Bloch equations easy to handle. Some unpublished implementation details are given along with some theoretical results concerning the convergence of the hard pulse train approximation and the prediction of the energy deposition. The same tools are subsequently used to obtain a simplified model of the CPMG and SSFP sequences. The echo to echo rotation is studied and the natural stabilization of the signals is explained by the dispersion of phase. The relaxation processes during such sequences are also modelled in a simplified but widely applicable manner. A previous polynomials stabilization algorithm is explained in terms of a discrete version of the adiabatic principle. The last chapter tackles with a non-CPMG sequence which is insensitive to the initial phase of the magnetization. This sequence is based on a quadratic phase modulation of the RF pulse train.
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Contributor : Patrick Le Roux <>
Submitted on : Wednesday, January 31, 2007 - 5:46:00 PM
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  • HAL Id : tel-00128349, version 1



Patrick Le Roux. Suites Régulières d'Impulsions Radio-Fréquence en Résonance Magnétique. Application à l'IRM.. Physique [physics]. Université Paris Sud - Paris XI, 2006. Français. ⟨tel-00128349⟩



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