A Krylov Subspace Approach to Parametric Inversion of Electromagnetic Data Based on Residual Minimization

In this thesis we present a Krylov subspace technique and use residual minimization to efficiently solve parametric electromagnetic inversion problems. We exploit the shift-invariance property of Krylov subspaces to compute total fields inside a homogeneous object for a whole range of contrast values. As soon as these fields are found, we can determine the corresponding scattered fields in a straightforward manner. This approach allows us to solve the inverse problem by simply inspecting an objective function which measures the discrepancy between the measured and modeled scattered field data.Inverse ScatteringLaboratory of Electromagnetic ResearchElectrical Engineering, Mathematics and Computer Scienc

B1-based SAR reconstruction using contrast source inversion–electric properties tomography (CSI-EPT)

Specific absorption rate (SAR) assessment is essential for safety purposes during MR acquisition. Online SAR assessment is not trivial and requires, in addition, knowledge of the electric tissue properties and the electric fields in the human anatomy. In this study, the potential of the recently developed CSI-EPT method to reconstruct SAR distributions is investigated. This method is based on integral representations for the electromagnetic field and attempts to reconstruct the tissue parameters and the electric field strength based on B+1B1+ field data only. Full three-dimensional FDTD simulations using a female pelvis model are used to validate two-dimensional CSI reconstruction results in the central transverse plane of a 3T body coil. Numerical experiments demonstrate that the reconstructed SAR distributions are in good agreement with the SAR distributions as determined via 3D FDTD simulations and show that these distributions can be computed very efficiently in the central transverse plane of a body coil with the two-dimensional approach of CSI-EPT.Circuits and System