title: Comparison of block and event-related experimental designs in diffusion-weighted functional MRI.
abstract: OBJECTIVE
  To compare diffusion-weighted functional magnetic resonance imaging (DfMRI), a novel alternative to the blood oxygenation level-dependent (BOLD) contrast, in a functional MRI experiment.
  
  
  METHODS
  Nine participants viewed contrast reversing (7.5 Hz) black-and-white checkerboard stimuli using block and event-related paradigms. DfMRI (b = 1800 mm/s(2)) and BOLD sequences were acquired. Four parameters describing the observed signal were assessed: percent signal change, spatial extent of the activation, the Euclidean distance between peak voxel locations, and the time-to-peak of the best fitting impulse response for different paradigms and sequences.
  
  
  RESULTS
  The BOLD conditions showed a higher percent signal change relative to DfMRI; however, event-related DfMRI showed the strongest group activation (t = 21.23, P < 0.0005). Activation was more diffuse and spatially closer to the BOLD response for DfMRI when the block design was used. DfMRIevent showed the shortest TTP (4.4 ± 0.88 sec).
  
  
  CONCLUSIONS
  The hemodynamic contribution to DfMRI may increase with the use of block designs.
authors.affiliation: University of Queensland, Centre for Advanced Imaging, Brisbane, Australia; University of Queensland, Queensland Brain Institute, Brisbane, Australia.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Williams
authors.forename: Katie L
authors.initials: KL
authors.lastname: McMahon
authors.forename: Julia
authors.initials: J
authors.lastname: Hocking
authors.forename: David C
authors.initials: DC
authors.lastname: Reutens
mesh_terms: D000328:Adult; D000465:Algorithms; D001931:Brain Mapping / Q000379:methods*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012107:Research Design; D012680:Sensitivity and Specificity; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult
keywords: BOLD; DfMRI; diffusion; experimental design; fMRI; visual cortex