title: BOLD signal in memory paradigms in hippocampal region depends on echo time.
abstract: OBJECTIVE
  To evaluate the hypothesis that the entire hippocampus might be affected by susceptibility artifacts. Previous studies described susceptibility artifacts in the amygdala and the anterior hippocampus.
  
  
  METHODS
  We investigated 20 subjects with a verbal memory paradigm aiming at testing two different TEs (45 vs. 64 msec) at 1.5 T for hippocampal blood oxygenation level-dependent (BOLD) activity. T2* maps were calculated from the normalized mean echo-planar imaging (EPI) of the two echo times (TEs).
  
  
  RESULTS
  Within the hippocampal region of interest (ROI), the amount of suprathreshold voxels was significantly higher at TE = 64 msec compared to TE = 45 msec. When corrected for multiple comparisons (family-wise error [FWE] in a small volume of interest, P < 0.05) we no longer found significant activations at TE = 45 msec, while a significant number of voxels remained after the small volume correction (P < 0.05, FWE) within the ROI at TE = 64 msec.
  
  
  CONCLUSIONS
  Although a shorter TE demonstrates advantages, a TE of 45 msec leads to a significant loss of BOLD signal detection in memory functional magnetic resonance imaging (fMRI) studies when compared to 64 msec. We assume that the hippocampal region, even the anterior part, is not strongly affected by susceptibility gradients.
authors.affiliation: Department of Neurosurgery, University of Tuebingen, Tuebingen, Germany. monika.milian@med.uni-tuebingen.de
authors.forename: Monika
authors.initials: M
authors.lastname: Milian
authors.forename: Lena
authors.initials: L
authors.lastname: Zeltner
authors.forename: Silke
authors.initials: S
authors.lastname: Klamer
authors.forename: Uwe
authors.initials: U
authors.lastname: Klose
authors.forename: Sabine
authors.initials: S
authors.lastname: Rona
authors.forename: Michael
authors.initials: M
authors.lastname: Erb
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D001931:Brain Mapping / Q000379:methods*; D005260:Female; D006624:Hippocampus / Q000033:anatomy & histology / Q000502:physiology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008568:Memory / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity