title: Characterization and correction of eddy-current artifacts in unipolar and bipolar diffusion sequences using magnetic field monitoring.
abstract: Diffusion tensor imaging (DTI) of moving organs is gaining increasing attention but robust performance requires sequence modifications and dedicated correction methods to account for system imperfections. In this study, eddy currents in the "unipolar" Stejskal-Tanner and the velocity-compensated "bipolar" spin-echo diffusion sequences were investigated and corrected for using a magnetic field monitoring approach in combination with higher-order image reconstruction. From the field-camera measurements, increased levels of second-order eddy currents were quantified in the unipolar sequence relative to the bipolar diffusion sequence while zeroth and linear orders were found to be similar between both sequences. Second-order image reconstruction based on field-monitoring data resulted in reduced spatial misalignment artifacts and residual displacements of less than 0.43 mm and 0.29 mm (in the unipolar and bipolar sequences, respectively) after second-order eddy-current correction. Results demonstrate the need for second-order correction in unipolar encoding schemes but also show that bipolar sequences benefit from second-order reconstruction to correct for incomplete intrinsic cancellation of eddy-currents.
authors.affiliation: Centre for Medical Imaging, University College London, London, United Kingdom. Electronic address: rachel.chan.ucl@gmail.com.
authors.forename: Rachel W
authors.initials: RW
authors.lastname: Chan
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Constantin
authors.initials: C
authors.lastname: von Deuster
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Daniel
authors.initials: D
authors.lastname: Giese
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
authors.forename: Christian T
authors.initials: CT
authors.lastname: Stoeck
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Jack
authors.initials: J
authors.lastname: Harmer
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Aitken
authors.affiliation: Centre for Medical Imaging, University College London, London, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Atkinson
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Kozerke
keywords: Eddy-current correction; Field monitoring; Higher-order eddy-currents