# An Algebraic Method to Synthesize Specified Modal Currents in Ladder Resonators: Application to Non-circular Birdcage Coils

• Author(s) / Creator(s)
• This is the peer reviewed version of the following article: Magn Reson Med. 2015 Nov;74(5):1470-81, which has been published in final form at https://doi.org/10.1002/mrm.25503. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

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, transverse electromagnetic (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 3 Tesla.

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.

CONCLUSION:
The algebraic method overcomes the inability of the existing inductance equalization method to account for all elements of the inductance matrix and the inability to accommodate modal currents that are not (co)sinusoidal.

• Date created
2014-11-13
• Subjects / Keywords
• Type of Item
Article (Published)
• DOI
https://doi.org/10.7939/r3-6fjy-1051