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Imagerie par résonance magnétique à haute résolution temporelle: Développement d'une méthode d'acquisition parallèle tridimensionnelle pour l'imagerie fonctionnelle cérébrale

Abstract : Echo Planar Imaging is widely used to perform data acquisition in functional neuroimaging. This sequence allows the acquisition of a set of about 30 slices, covering the whole brain, at a spatial resolution ranging from 2 to 4 mm, and a temporal resolution ranging from 1 to 2 s. It is thus well adapted to the mapping of activated brain areas but does not allow precise study of the brain dynamics. Moreover, temporal interpolation is needed in order to correct for inter-slices delays and 2D acquisition is subject to vascular inflow artifacts. To improve the estimation of the hemodynamic response functions associated with activation, this thesis aimed at developping a 3D high temporal resolution acquisition method. To do so, Echo Volume Imaging was combined with reduced field-of-view acquisition and parallel imaging. Indeed, EVI allows the acquisition of a whole volume in Fourier space following a single excitation, but it requires very long echo trains. Parallel imaging and field-of-view reduction are used to reduce the echo train durations by a factor of 4, which allows the acquisition of a 3D brain volume with limited susceptibility-induced distortions and signal losses, in 200 ms. All imaging parameters have been optimized in order to reduce echo train durations and to maximize SNR, so that cerebral activation can be detected with a high level of confidence. Robust detection of brain activation was demonstrated with both visual and auditory paradigms. High temporal resolution hemodynamic response functions could be estimated through selective averaging of the response to the different trials of the stimulation. To further improve SNR, the matrix inversions required in parallel reconstruction were regularized, and the impact of the level of regularization on activation detection was investigated. Eventually, potential applications of parallel EVI such as the study of non-stationary effects in the BOLD response.
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https://tel.archives-ouvertes.fr/tel-00204555
Contributor : Cécile Rabrait <>
Submitted on : Monday, January 14, 2008 - 8:44:34 PM
Last modification on : Friday, September 11, 2015 - 10:00:04 AM
Long-term archiving on: : Thursday, September 27, 2012 - 2:15:33 PM

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Cécile Rabrait. Imagerie par résonance magnétique à haute résolution temporelle: Développement d'une méthode d'acquisition parallèle tridimensionnelle pour l'imagerie fonctionnelle cérébrale. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2007. Français. ⟨tel-00204555⟩

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