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Exploring the human brain using magnetic resonance imaging and parallel transmission at ultra-high field

Final Report Summary - EXPAT (Exploring the human brain using magnetic resonance imaging and parallel transmission at ultra-high field)

The EXPAT project aimed at solving the radiofrequency field inhomogeneity problem ubiquitously encountered in head MRI at ultra-high field. Tools, methods and validations were performed at 7T to prepare for investigations at 11.7T. The RF field inhomogeneity problem is considered of utmost importance in MRI at ultra-high field. Without measures or efforts to compensate for it, it can potentially result in zones of shade and suboptimal signal to noise ratio, seriously hindering the potential of high field scanners. The technology that was central in the project to solve the problem is parallel transmission. During the first half of the project, efforts were invested to develop the tools to exploit the technology in a powerful manner. It included safety (specific absorption rate or SAR) simulations and validations, efficient and fast RF pulse design algorithms under explicat hardware and safety constraints, and in-vitro/in-vivo validations. As initially proposed, it was furthermore demonstrated that MR scan performance (e.g. flip angle homogeneity, acquisition speed) could be gained if temperature, instead of SAR, was monitored (numerically or experimentally) during the exams. Further work however is needed to validate the underlying thermal model. The second half of the project mostly consisted of applying and providing experimental verifications of the usefulness of the proposed developments with anatomical (T1, T2 and T2*-weighted scans) and also functional data (2D, 3D). The main outcome of the project can be considered a success given that the RF field inhomogeneity problem is no longer an obstacle for human head MRI at 7T. Novel and original approaches based on parallel transmission and inspired from quantum theory were developed during the project and successfully tested in vivo. Importantly, efforts have been invested to implement powerful solutions easily, i.e. without requiring any particular expertise and at no time penalty for the user. The project thus gave birth to plug and play powerful solutions that will hopefully help democratizing the use of high field scanners in the near future.