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Parallel transmission for magnetic resonance imaging of the human brain at ultra high field : specific absorption rate control & flip-angle homogenization

Abstract : The focus of this thesis lies on the development, and implementation, of parallel transmission (pTx) techniques in magnetic resonance imaging for flip-angle homogenization throughout the human brain at ultra-high field. In order to allow in-vivo demonstrations, a conservative yet viable safety concept is introduced to control the absorbed radiofrequency (RF) power . Subsequently, novel methods for local SAR control and non-selective RF pulse-design are investigated. The impact of these short and energy-efficient waveforms, referred to as kT-points, is first demonstrated in the context of the small-tip-angle domain. Targeting a larger scope of applications, the kT-points design is then generalized to encompass large flip angle excitations and inversions. This concept is applied to one of the most commonly used T1-weighted sequences in neuroimaging. Results thus obtained at 7 Tesla are compared to images acquired with a clinical setup at 3 Tesla, validating the principles of the kT-points method and demonstrating that pTx-enabled ultra-high field systems can also be competitive in the context of T1-weighted imaging. Finally, simplifications in the global design of the pTx-implementation are studied in order to obtain a more cost-effective solution.
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Submitted on : Sunday, September 16, 2012 - 1:01:25 AM
Last modification on : Friday, June 12, 2020 - 8:21:55 PM
Long-term archiving on: : Monday, December 17, 2012 - 2:30:14 AM

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  • HAL Id : tel-00732658, version 1

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Martijn Anton Hendrik Cloos. Parallel transmission for magnetic resonance imaging of the human brain at ultra high field : specific absorption rate control & flip-angle homogenization. Other [cond-mat.other]. Université Paris Sud - Paris XI, 2012. English. ⟨NNT : 2012PA112066⟩. ⟨tel-00732658⟩

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