Physical Insights from Ideal Current Patterns Resulting in Ultimate Intrinsic SNR: Efficacy of Traditional Coil Designs at Low Field Strength & the Need for New Designs at High Field

Riccardo Lattanzi^1,2, Daniel K. Sodickson^1,2

Using a rigorous full-wave electrodynamic formulation based on dyadic Greens functions (DGF), we calculate ideal current patterns that result in the highest possible signal-to-noise ratio (SNR) in homogeneous spherical and cylindrical samples, and compare the resulting patterns to familiar coil designs. Our results demonstrate the natural emergence of quadrature birdcage-like reception current patterns for imaging near the center of the object, as opposed to distributed loop-butterfly surface quadrature patterns for locations closer to the surface. Ideal current patterns become more complex at high field, indicating that innovative coil designs may be needed in order to approach the optimal performance.