Jiaen Liu1, Xiaotong Zhang1, Sebastian Schmitter2, Pierre-Francois Van de Moortele2, Bin He1,3. 1. Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, USA. 2. Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA. 3. Institute for Engineering in Medicine, University of Minnesota, Minneapolis, Minnesota, USA.
Abstract
PURPOSE: 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. THEORY AND 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. CONCLUSION: The proposed gEPT approach holds promises to improve EP mapping quality by recovering the boundary information and enhancing robustness against noise.
PURPOSE: 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. THEORY AND 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. CONCLUSION: The proposed gEPT approach holds promises to improve EP mapping quality by recovering the boundary information and enhancing robustness against noise.
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