Citation

Pfrommer A, Henning A. Magn. Reson. Med. 2018; 80(5): 2122-2138.

Affiliation

Ernst-Moritz-Arndt University Greifswald, Institute of Physics, Greifswald, Germany.

Copyright

(Copyright © 2018, John Wiley and Sons)

DOI

10.1002/mrm.27169

PMID

29536567

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.

© 2018 International Society for Magnetic Resonance in Medicine.

Language: en

Keywords

RF coils; dipole antenna; dyadic Green's functions; electromagnetic simulation; realistic body model; ultimate intrinsic SNR