Ariane Fillmer1, Signe Johanna Vannesjo1, Matteo Pavan1, Milan Scheidegger1,2, Klaas Paul Pruessmann1, Anke Henning1,3. 1. Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland. 2. Clinic of Affective Disorders and General Psychiatry, University Hospital of Psychiatry Zurich, Zurich, Switzerland. 3. Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.
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.
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.
Authors: Vincent Oltman Boer; Jan Ole Pedersen; Nick Arango; Irene Kuang; Jason Stockmann; Esben Thade Petersen Journal: MAGMA Date: 2022-05-05 Impact factor: 2.310
Authors: Simone A Winkler; Paul A Warr; Jason P Stockmann; Azma Mareyam; Boris Keil; Ronald D Watkins; Lawrence L Wald; Brian K Rutt Journal: Concepts Magn Reson Part B Magn Reson Eng Date: 2018-06-07 Impact factor: 1.176
Authors: Hoby P Hetherington; Chan Hong Moon; Michael Schwerter; Nadim Joni Shah; Jullie W Pan Journal: Magn Reson Med Date: 2020-08-28 Impact factor: 4.668
Authors: Vincent O Boer; Mads Andersen; Anna Lind; Nam Gyun Lee; Anouk Marsman; Esben T Petersen Journal: Magn Reson Med Date: 2020-02-14 Impact factor: 4.668
Authors: H Michael Gach; Austen N Curcuru; Erin J Wittland; Borna Maraghechi; Bin Cai; Sasa Mutic; Olga L Green Journal: J Appl Clin Med Phys Date: 2019-09-21 Impact factor: 2.102