Fast iterative pre-emphasis calibration method enabling third-order dynamic shim updated fMRI

Ariane Fillmer, Signe Johanna Vannesjo, Matteo Pavan, Milan Scheidegger, Klaas Paul Pruessmann, Anke Henning

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

Purpose To calibrate a pre-emphasis to sufficiently compensate eddy currents for application of dynamic shim updating to fMRI without extension of scan times. Methods Eddy current effects induced into all shim terms up to third-order were characterized by spatiotemporal field monitoring, using a third-order field camera. Pre-emphasis settings were derived from the measurements and iteratively evaluated and refined. The calibrated pre-emphasis was applied to slice-wise dynamic shim updating in combination with a dynamic excitation frequency (F0) determination and a slice-wise B0 optimization routine for in vivo echo planar imaging and resting-state functional MRI. Results The described method for pre-emphasis calibration led to settling times of remaining eddy current effects below 2 ms, allowing for the application of dynamic shim updating to fMRI without extension of scan times or induction of eddy current related artifacts. A dynamic F0 determination compensates frequency shifts induced by the superposition of different shim fields, and therefore, prevents an image shift within the field of view. Hardware limitations necessitate the reduction of the maximum applicable B0 shim field amplitudes and restrict the shim performance. Conclusion The proposed method enables accurate pre-emphasis calibration, and therefore, the application of dynamic shim updating to fMRI.

Original languageEnglish (US)
Pages (from-to)1119-1131
Number of pages13
JournalMagnetic resonance in medicine
Volume75
Issue number3
DOIs
StatePublished - Mar 1 2016
Externally publishedYes

Keywords

  • B shimming
  • dynamic shim updating
  • eddy current compensation
  • pre-emphasis calibration
  • resting-state fMRI
  • spatio-temporal field monitoring

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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