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Influence de l'intensité du champ magnétique sur l'imagerie RMN des poumons à l'aide d'hélium-3 hyperpolarisé

Abstract : Chronic obstructive pulmonary diseases are the forth cause of mortality in Europe. Available techniques only give a late assessment in the disease process. A new technique has been proposed in 1994: magnetic resonance imaging (MRI) of hyperpolarized (HP) gases. Lungs are a large interface between gas and tissue. In a magnetic field (B0), the difference of magnetic susceptibility between both media causes faster signal decay. This effect increases with B0. We have two scanners with different B0s (0.1 T and 1.5 T) and an optical pumping system to produce hyperpolarized helium-3 (3He) so we studied quantitatively the influence of B0 on 3He HP MRI in the lungs. First, the needed theoretical bases and an exhaustive list of materials to carry out this study are presented. Then we have observed that the transverse relaxation time of HP 3He for a spin echo train sequence, T2cpmg, increases when B0 decreases. A two decade magnitude variation has been observed between 0.1 T and 1.5 T. Some studies on an animal model (rat) have shown that T2cpmg has a sensitivity to lung filling which is equivalent to that of the apparent diffusion coefficient, and that with the injection of a super paramagnetic agent, the lung susceptibility effect can be matched. We also measured an increase of the lifetime of the HP 3He signal, T2*, in the lungs for lower B0. Finally we compared the signal to noise ratio (SNR) on both scanners. In conclusion even if the T2* increase at low B0 is good for SNR, this effect is limited and the use of high field scanners is not an inconvenient for this application.
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Contributor : Alexandre Vignaud <>
Submitted on : Friday, October 31, 2003 - 2:02:18 PM
Last modification on : Wednesday, September 16, 2020 - 5:04:23 PM
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Alexandre Vignaud. Influence de l'intensité du champ magnétique sur l'imagerie RMN des poumons à l'aide d'hélium-3 hyperpolarisé. Physique [physics]. Université Paris Sud - Paris XI, 2003. Français. ⟨tel-00003668⟩

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