An Algebraic Method to Synthesize Specified Modal Currents in Ladder Resonators: Application to Non-circular Birdcage Coils Nicola De Zanchea and Klaas P. Pruessmannb a. Division of Medical Physics, Department of Oncology, University of Alberta, Edmonton, Canada b. Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland Published in Magnetic Resonance in Medicine DOI: 10.1002/mrm.25503 Correspondence Address: Nicola De Zanche Division of Medical Physics Department of Oncology University of Alberta 11560 University Avenue Edmonton, Alberta T6G 1Z2 Canada E-mail:
[email protected] Phone: + 1-780-989-8155 Fax: + 1-780-432-8615 1 Abstract Purpose: Detectors such as birdcage coils often consist of networks of coupled resonant circuits that must produce specified magnetic field distributions. In many cases, such as quadrature asymmetric insert body coils, calculating the capacitance values required to achieve specified currents and frequencies simultaneously is a challenging task that previously had only approximate or computationally-inefficient solutions. Theory and Methods: A general algebraic method was developed that is applicable to linear networks having planar representations such as birdcage coils, TEM coils, and numerous variants of ladder networks. Unlike previous iterative or approximate methods, the algebraic method is computationally efficient and determines current distribution and resonant frequency using a single matrix inversion. The method was demonstrated by specifying irregular current distributions on a highly elliptical birdcage coil at 3T. Results Measurements of the modal frequency spectrum and transmit field distribution of the two specified modes agrees with the theory. Accuracy is limited in practice only by how accurately the matrix of self and mutual inductances of the network is known.