title: On the Contribution of Curl-Free Current Patterns to the Ultimate Intrinsic Signal-to-Noise Ratio at Ultra-High Field Strength.
abstract: The ultimate intrinsic signal-to-noise ratio (SNR) is a coil independent performance measure to compare different receive coil designs. To evaluate this benchmark in a sample, a complete electromagnetic basis set is required. The basis set can be obtained by curl-free and divergence-free surface current distributions, which excite linearly independent solutions to Maxwell's equations. In this work, we quantitatively investigate the contribution of curl-free current patterns to the ultimate intrinsic SNR in a spherical head-sized model at 9.4 T. Therefore, we compare the ultimate intrinsic SNR obtained with having only curl-free or divergence-free current patterns, with the ultimate intrinsic SNR obtained from a combination of curl-free and divergence-free current patterns. The influence of parallel imaging is studied for various acceleration factors. Moreover results for different field strengths (1.5 T up to 11.7 T) are presented at specific voxel positions and acceleration factors. The full-wave electromagnetic problem is analytically solved using dyadic Green's functions. We show, that at ultra-high field strength (B0⩾7T) a combination of curl-free and divergence-free current patterns is required to achieve the best possible SNR at any position in a spherical head-sized model. On 1.5- and 3T platforms, divergence-free current patterns are sufficient to cover more than 90% of the ultimate intrinsic SNR.
authors.affiliation: Max Planck Institute for Biological Cybernetics, High-Field Magnetic Resonance Center, Tuebingen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Pfrommer
authors.affiliation: Max Planck Institute for Biological Cybernetics, High-Field Magnetic Resonance Center, Tuebingen, Germany.|Ernst-Moritz-Arndt University Greifswald, Institute of Physics, Greifswald, Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Henning
mesh_terms: D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging* / Q000502:physiology*; D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods; D008959:Models, Neurological; D011829:Radiation Dosage; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio
keywords: RF coils; dipole antenna; dyadic Green's functions; electrodynamics; ultimate intrinsic SNR