title: Is DARTEL-based voxel-based morphometry affected by width of smoothing kernel and group size? A study using simulated atrophy.
abstract: OBJECTIVE
  To quantify to what extent the new registration method, DARTEL (Diffeomorphic Anatomical Registration Through Exponentiated Lie Algebra), may reduce the smoothing kernel width required and investigate the minimum group size necessary for voxel-based morphometry (VBM) studies.
  
  
  METHODS
  A simulated atrophy approach was employed to explore the role of smoothing kernel, group size, and their interactions on VBM detection accuracy. Group sizes of 10, 15, 25, and 50 were compared for kernels between 0-12 mm.
  
  
  RESULTS
  A smoothing kernel of 6 mm achieved the highest atrophy detection accuracy for groups with 50 participants and 8-10 mm for the groups of 25 at P < 0.05 with familywise correction. The results further demonstrated that a group size of 25 was the lower limit when two different groups of participants were compared, whereas a group size of 15 was the minimum for longitudinal comparisons but at P < 0.05 with false discovery rate correction.
  
  
  CONCLUSIONS
  Our data confirmed DARTEL-based VBM generally benefits from smaller kernels and different kernels perform best for different group sizes with a tendency of smaller kernels for larger groups. Importantly, the kernel selection was also affected by the threshold applied. This highlighted that the choice of kernel in relation to group size should be considered with care.
authors.affiliation: Centre for Integrative Neuroscience and Neurodynamics, University of Reading, Reading, UK. shan.shen@reading.ac.uk
authors.forename: Shan
authors.initials: S
authors.lastname: Shen
authors.forename: Annette
authors.initials: A
authors.lastname: Sterr
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001284:Atrophy / Q000473:pathology; D001921:Brain / Q000473:pathology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010363:Pattern Recognition, Automated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult