title: Retrospective head motion correction approaches for diffusion tensor imaging: Effects of preprocessing choices on biases and reproducibility of scalar diffusion metrics.
abstract: OBJECTIVE
  To evaluate how retrospective head motion correction strategies affect the estimation of scalar metrics commonly used in clinical diffusion tensor imaging (DTI) studies along with their across-session reproducibility errors.
  
  
  METHODS
  Fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD) and their respective across-session reproducibility errors were measured on a 4T test-retest dataset of healthy participants using five processing pipelines. These differed in: 1) the number of b0 volumes used for motion correction reference (one or five); 2) the estimations of the gradient matrix rotation (based on 6 or 12 degrees of freedom derived from coregistration); and 3) the software packages used (FSL or DTIPrep). Biases and reproducibility were evaluated in three regions of interest (ROIs) (bilateral arcuate fasciculi, cingula, and the corpus callosum) and also at the full brain level with tract based skeleton images.
  
  
  RESULTS
  Preprocessing choices affected DTI measures and their reproducibility. The DTIPrep pipeline exhibited higher DTI metrics: FA/MD and AD (P < 0.05) relative to FSL pipelines both at the ROI and full brain level, and lower RD estimates (P < 0.05) at the ROI level. Within FSL pipelines no such effects were found (P-values ranging between 0.25 and 0.97). The DTIPrep pipeline showed the highest number of white matter skeleton voxels, with significantly higher reproducibility (P < 0.001) relative to the other pipelines (tested on P < 0.01 uncorrected maps).
  
  
  CONCLUSIONS
  The use of an iteratively averaged b0 image as motion correction reference (as performed by DTIPrep) affects both scalar values and improves test-retest reliability relative to the other tested pipelines. These considerations are potentially relevant for data analysis in longitudinal DTI studies.
authors.affiliation: Center for Mind/Brain Sciences (CIMEC), University of Trento, Rovereto, Italy.|Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: Barbara A K
authors.initials: BA
authors.lastname: Kreilkamp
authors.affiliation: Center for Mind/Brain Sciences (CIMEC), University of Trento, Rovereto, Italy.
authors.forename: Domenico
authors.initials: D
authors.lastname: Zacà
authors.affiliation: Department of Neurology, University of California San Francisco, San Francisco, California, USA.
authors.forename: Nico
authors.initials: N
authors.lastname: Papinutto
authors.affiliation: Center for Mind/Brain Sciences (CIMEC), University of Trento, Rovereto, Italy.
authors.forename: Jorge
authors.initials: J
authors.lastname: Jovicich
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000033:anatomy & histology*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D019416:Head Movements; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D009038:Motion; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
keywords: DTIPrep; FSL; diffusion magnetic resonance imaging; diffusion tensor; head motion correction; reproducibility