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.
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 RFcoil 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.
Authors: Gregor Adriany; Pierre-Francois Van de Moortele; Florian Wiesinger; Steen Moeller; John P Strupp; Peter Andersen; Carl Snyder; Xiaoliang Zhang; Wei Chen; Klaas P Pruessmann; Peter Boesiger; Tommy Vaughan; Kāmil Uğurbil Journal: Magn Reson Med Date: 2005-02 Impact factor: 4.668
Authors: William Grissom; Chun-yu Yip; Zhenghui Zhang; V Andrew Stenger; Jeffrey A Fessler; Douglas C Noll Journal: Magn Reson Med Date: 2006-09 Impact factor: 4.668
Authors: Christof Thalhammer; Wolfgang Renz; Lukas Winter; Fabian Hezel; Jan Rieger; Harald Pfeiffer; Andreas Graessl; Frank Seifert; Werner Hoffmann; Florian von Knobelsdorff-Brenkenhoff; Valeriy Tkachenko; Jeanette Schulz-Menger; Peter Kellman; Thoralf Niendorf Journal: J Magn Reson Imaging Date: 2012-06-15 Impact factor: 4.813
Authors: Ryan Brown; Guillaume Madelin; Riccardo Lattanzi; Gregory Chang; Ravinder R Regatte; Daniel K Sodickson; Graham C Wiggins Journal: Magn Reson Med Date: 2012-08-08 Impact factor: 4.668