Ideal current patterns yielding optimal signal-to-noise ratio and specific absorption rate in magnetic resonance imaging: Computational methods and physical insights

Riccardo Lattanzi, Daniel K. Sodickson

    Research output: Contribution to journalArticle

    Abstract

    At high and ultra-high magnetic field strengths, understanding interactions between tissues and the electromagnetic fields generated by radiofrequency coils becomes crucial for safe and effective coil design as well as for insight into limits of performance. In this work, we present a rigorous electrodynamic modeling framework, using dyadic Green's functions, to derive the electromagnetic field in homogeneous spherical and cylindrical samples resulting from arbitrary surface currents in the presence or absence of a surrounding radiofrequency shield. We show how to calculate ideal current patterns that result in the highest possible signal-to-noise ratio (ultimate intrinsic signal-to-noise ratio) or the lowest possible radiofrequency power deposition (ultimate intrinsic specific absorption rate) compatible with electrodynamic principles. We identify familiar coil designs within optimal current patterns at low to moderate field strength, thereby establishing and explaining graphically the near-optimality of traditional surface and volume quadrature designs. We also document the emergence of less familiar patterns, e.g., involving substantial electric- as well as magnetic-dipole contributions, at high field strength. Performance comparisons with particular coil array configurations demonstrate that optimal performance may be approached with finite arrays if ideal current patterns are used as a guide for coil design.

    Original languageEnglish (US)
    Pages (from-to)286-304
    Number of pages19
    JournalMagnetic resonance in medicine
    Volume68
    Issue number1
    DOIs
    StatePublished - Jul 1 2012

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    Keywords

    • Dyadic Green's function
    • Electrodynamics
    • Parallel excitation
    • Parallel imaging
    • Parallel transmission
    • RF coils
    • RF shimming
    • Ultimate intrinsic SAR
    • Ultimate intrinsic SNR

    ASJC Scopus subject areas

    • Radiology Nuclear Medicine and imaging

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