Dual optimization method of radiofrequency and quasistatic field simulations for reduction of eddy currents generated on 7T radiofrequency coil shielding.

Authors

Yujuan Zhao, Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
Tiejun Zhao, Siemens Medical Solutions, Pittsburgh, Pennsylvania, USA
Shailesh B Raval, Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA & Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
Narayanan Krishnamurthy, Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
Hai Zheng, Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
Chad T Harris, Department of Physics and Astronomy, University of Western Ontario, London, Canada
William B Handler, Department of Physics and Astronomy, University of Western Ontario, London, Canada
Blaine A Chronik, Department of Physics and Astronomy, University of Western Ontario, London, Canada
Tamer S Ibrahim, Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA & Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA

Document Type

Article

Publication Date

11-1-2015

Journal

Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine

Volume

74

Issue

5

First Page

1461

Last Page

1469

URL with Digital Object Identifier

10.1002/mrm.25424

Abstract

PURPOSE: To optimize the design of radiofrequency (RF) shielding of transmit coils at 7T and reduce eddy currents generated on the RF shielding when imaging with rapid gradient waveforms.

METHODS: One set of a four-element, 2 × 2 Tic-Tac-Toe head coil structure was selected and constructed to study eddy currents on the RF coil shielding. The generated eddy currents were quantitatively studied in the time and frequency domains. The RF characteristics were studied using the finite difference time domain method. Five different kinds of RF shielding were tested on a 7T MRI scanner with phantoms and in vivo human subjects.

RESULTS: The eddy current simulation method was verified by the measurement results. Eddy currents induced by solid/intact and simple-structured slotted RF shielding significantly distorted the gradient fields. Echo-planar images, B1+ maps, and S matrix measurements verified that the proposed slot pattern suppressed the eddy currents while maintaining the RF characteristics of the transmit coil.

CONCLUSION: The presented dual-optimization method could be used to design RF shielding and reduce the gradient field-induced eddy currents while maintaining the RF characteristics of the transmit coil.