Andreas Pfrommer1, Anke Henning1,2. 1. Max Planck Institute for Biological Cybernetics, High-Field Magnetic Resonance Center, Tuebingen, Germany. 2. Ernst-Moritz-Arndt University Greifswald, Institute of Physics, Greifswald, Germany.
Abstract
PURPOSE: The ultimate intrinsic signal-to-noise ratio (UISNR) represents an upper bound for the achievable SNR of any receive coil. To reach this threshold a complete basis set of equivalent surface currents is required. This study systematically investigated to what extent either loop- or dipole-like current patterns are able to reach the UISNR threshold in a realistic human head model between 1.5 T and 11.7 T. Based on this analysis, we derived guidelines for coil designers to choose the best array element at a given field strength. Moreover, we present ideal current patterns yielding the UISNR in a realistic body model. METHODS: We distributed generic current patterns on a cylindrical and helmet-shaped surface around a realistic human head model. We excited electromagnetic fields in the human head by using eigenfunctions of the spherical and cylindrical Helmholtz operator. The electromagnetic field problem was solved by a fast volume integral equation solver. RESULTS: At 7 T and above, adding curl-free current patterns to divergence-free current patterns substantially increased the SNR in the human head (locally >20%). This was true for the helmet-shaped and the cylindrical surface. On the cylindrical surface, dipole-like current patterns had high SNR performance in central regions at ultra-high field strength. The UISNR increased superlinearly with B0 in most parts of the cerebrum but only sublinearly in the periphery of the human head. CONCLUSION: The combination of loop and dipole elements could enhance the SNR performance in the human head at ultra-high field strength.
PURPOSE: The ultimate intrinsic signal-to-noise ratio (UISNR) represents an upper bound for the achievable SNR of any receive coil. To reach this threshold a complete basis set of equivalent surface currents is required. This study systematically investigated to what extent either loop- or dipole-like current patterns are able to reach the UISNR threshold in a realistic human head model between 1.5 T and 11.7 T. Based on this analysis, we derived guidelines for coil designers to choose the best array element at a given field strength. Moreover, we present ideal current patterns yielding the UISNR in a realistic body model. METHODS: We distributed generic current patterns on a cylindrical and helmet-shaped surface around a realistic human head model. We excited electromagnetic fields in the human head by using eigenfunctions of the spherical and cylindrical Helmholtz operator. The electromagnetic field problem was solved by a fast volume integral equation solver. RESULTS: At 7 T and above, adding curl-free current patterns to divergence-free current patterns substantially increased the SNR in the human head (locally >20%). This was true for the helmet-shaped and the cylindrical surface. On the cylindrical surface, dipole-like current patterns had high SNR performance in central regions at ultra-high field strength. The UISNR increased superlinearly with B0 in most parts of the cerebrum but only sublinearly in the periphery of the human head. CONCLUSION: The combination of loop and dipole elements could enhance the SNR performance in the human head at ultra-high field strength.
Authors: Stephan Orzada; Klaus Solbach; Marcel Gratz; Sascha Brunheim; Thomas M Fiedler; Sören Johst; Andreas K Bitz; Samaneh Shooshtary; Ashraf Abuelhaija; Maximilian N Voelker; Stefan H G Rietsch; Oliver Kraff; Stefan Maderwald; Martina Flöser; Mark Oehmigen; Harald H Quick; Mark E Ladd Journal: PLoS One Date: 2019-09-12 Impact factor: 3.240
Authors: Karthik Lakshmanan; Martijn Cloos; Ryan Brown; Riccardo Lattanzi; Daniel K Sodickson; Graham C Wiggins Journal: Concepts Magn Reson Part B Magn Reson Eng Date: 2020-09-07 Impact factor: 1.176