title: Transient signal changes in diffusion-weighted stimulated echoes during neuronal stimulation at 3T.
abstract: OBJECTIVE
  To develop a sensitive method for detecting minute transient signal changes that can arise due to variations in the extravascular apparent self-diffusion coefficient, D, during neuronal activation.
  
  
  METHODS
  A three-pulse sequence that reads out a moderately diffusion-weighted (DW) primary echo (PRE) and a heavily DW stimulated echo (STE) was employed to investigate whether small transient signal changes in extravascular D occur in response to a visual stimulus. Contributions to signal changes caused by subtle differences in the transient variations of the apparent transverse relaxation constant, T(2), between the PRE and STE were also quantified.
  
  
  RESULTS
  On z-maps obtained from the STE, more voxels showed significant stimulus-related signal changes compared to maps of the PRE. The average maximum signal change of the STE was larger than that of the PRE. The observed increase in the relative signal change was independent of the strength of the diffusion weighting.
  
  
  CONCLUSIONS
  The STE is more sensitive to neuronal activity than the PRE. The discrepancy between the two echoes does not arise from transient changes in D, but from subtle differences in stimulus-related variations of T(2) between the two echoes.
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, 2021 6th Street SE, Minneapolis, MN 55455, USA. ute@cmrr.umn.edu
authors.forename: Ute
authors.initials: U
authors.lastname: Goerke
authors.forename: Harald E
authors.initials: HE
authors.lastname: Möller
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D010775:Photic Stimulation; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology*