title: Gradient-based electrical properties tomography (gEPT): A robust method for mapping electrical properties of biological tissues in vivo using magnetic resonance imaging.
abstract: OBJECTIVE
  To develop high-resolution electrical properties tomography (EPT) methods and investigate a gradient-based EPT (gEPT) approach that aims to reconstruct the electrical properties (EP), including conductivity and permittivity, of an imaged sample from experimentally measured B1 maps with improved boundary reconstruction and robustness against measurement noise.
  
  
  METHODS
  Using a multichannel transmit/receive stripline head coil with acquired B1 maps for each coil element, and by assuming negligible Bz component compared to transverse B1 components, a theory describing the relationship between B1 field, EP value, and their spatial gradient has been proposed. The final EP images were obtained through spatial integration over the reconstructed EP gradient. Numerical simulation, physical phantom, and in vivo human experiments at 7 T have been conducted to evaluate the performance of the proposed method.
  
  
  RESULTS
  Reconstruction results were compared with target EP values in both simulations and phantom experiments. Human experimental results were compared with EP values in literature. Satisfactory agreement was observed with improved boundary reconstruction. Importantly, the proposed gEPT method proved to be more robust against noise when compared to previously described nongradient-based EPT approaches.
  
  
  CONCLUSIONS
  The proposed gEPT approach holds promises to improve EP mapping quality by recovering the boundary information and enhancing robustness against noise.
authors.affiliation: Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Jiaen
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Xiaotong
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schmitter
authors.affiliation: Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Pierre-Francois
authors.initials: PF
authors.lastname: Van de Moortele
authors.affiliation: Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, USA.|Institute for Engineering in Medicine, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: He
mesh_terms: D001921:Brain / Q000502:physiology; D001931:Brain Mapping / Q000379:methods*; D055724:Electrophysiological Phenomena; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D014054:Tomography / Q000379:methods*
keywords: B1-mapping; EPT; electrical properties; gradient