title: Effects of image distortions originating from susceptibility variations and concomitant fields on diffusion MRI tractography results.
abstract: In this work we investigate the effects of echo planar imaging (EPI) distortions on diffusion tensor imaging (DTI) based fiber tractography results. We propose a simple experimental framework that would enable assessing the effects of EPI distortions on the accuracy and reproducibility of fiber tractography from a pilot study on a few subjects. We compare trajectories computed from two diffusion datasets collected on each subject that are identical except for the orientation of phase encode direction, either right-left (RL) or anterior-posterior (AP). We define metrics to assess potential discrepancies between RL and AP trajectories in association, commissural, and projection pathways. Results from measurements on a 3 Tesla clinical scanner indicated that the effects of EPI distortions on computed fiber trajectories are statistically significant and large in magnitude, potentially leading to erroneous inferences about brain connectivity. The correction of EPI distortion using an image-based registration approach showed a significant improvement in tract consistency and accuracy. Although obtained in the context of a DTI experiment, our findings are generally applicable to all EPI-based diffusion MRI tractography investigations, including high angular resolution (HARDI) methods. On the basis of our findings, we recommend adding an EPI distortion correction step to the diffusion MRI processing pipeline if the output is to be used for fiber tractography.
authors.affiliation: Program on Pediatric Imaging and Tissue Sciences, NICHD, National Institutes of Health, Bethesda, MD 20892, USA. irfanoglumo@mail.nih.gov
authors.forename: M Okan
authors.initials: MO
authors.lastname: Irfanoglu
authors.forename: Lindsay
authors.initials: L
authors.lastname: Walker
authors.forename: Joelle
authors.initials: J
authors.lastname: Sarlls
authors.forename: Stefano
authors.initials: S
authors.lastname: Marenco
authors.forename: Carlo
authors.initials: C
authors.lastname: Pierpaoli
mesh_terms: D000328:Adult; D000465:Algorithms; D001933:Brain Stem / Q000033:anatomy & histology / Q000502:physiology; D002531:Cerebellum / Q000166:cytology / Q000502:physiology; D003627:Data Interpretation, Statistical; D056324:Diffusion Tensor Imaging / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods; D005260:Female; D006179:Gyrus Cinguli / Q000166:cytology / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000502:physiology; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D010865:Pilot Projects; D015203:Reproducibility of Results