title: In vivo normative atlas of the hippocampal subfields using multi-echo susceptibility imaging at 7 Tesla.
abstract: OBJECTIVE
  To generate a high-resolution atlas of the hippocampal subfields using images acquired from 7 T, multi-echo, gradient-echo MRI for the evaluation of epilepsy and neurodegenerative disorders as well as investigating R2* (apparent transverse relaxation rate) and quantitative volume magnetic susceptibility (QS) of the subfields.
  
  
  METHODS
  Healthy control subjects (n=17) were scanned at 7 T using a multi-echo gradient-echo sequence and susceptibility-weighted magnitude images, R2* and QS maps were reconstructed. We defined a hippocampal subfield labeling protocol for the magnitude image produced from the average of all echoes and assessed reproducibility through volume and shape metrics. A group-wise diffeomorphic registration procedure was used to generate an average atlas of the subfields for the whole subject cohort. The quantitative MRI maps and subfield labels were then warped to the average atlas space and used to measure mean values of R2* and QS characterizing each subfield.
  
  
  RESULTS
  We were able to reliably label hippocampal subfields on the multi-echo susceptibility images. The group-averaged atlas accurately aligns these structures to produce a high-resolution depiction of the subfields, allowing assessment of both quantitative susceptibility and R2* across subjects. Our analysis of variance demonstrates that there are more apparent differences between the subfields on these quantitative maps than the normalized magnitude images.
  
  
  CONCLUSIONS
  We constructed a high-resolution atlas of the hippocampal subfields for use in voxel-based studies and demonstrated in vivo quantification of susceptibility and R2* in the subfields. This work is the first in vivo quantification of susceptibility values within the hippocampal subfields at 7 T.
authors: Imaging Research Laboratories, Robarts Research Institute, Western University, London, Ontario, Canada; Biomedical Engineering, Western University, London, Ontario, Canada.
authors: Maged
authors: M
authors: Goubran
authors: David A
authors: DA
authors: Rudko
authors: Brendan
authors: B
authors: Santyr
authors: Joe
authors: J
authors: Gati
authors: Trevor
authors: T
authors: Szekeres
authors: Terry M
authors: TM
authors: Peters
authors: Ali R
authors: AR
authors: Khan
mesh_terms: D000328:Adult; D000465:Algorithms; D000704:Analysis of Variance; D001271:Atlases as Topic; D015331:Cohort Studies; D005260:Female; D006624:Hippocampus / Q000033:anatomy & histology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D008297:Male; D009929:Organ Size; D012815:Signal Processing, Computer-Assisted
keywords: R2* mapping; hippocampal subfields; quantitative susceptibility mapping; ultra-high-field MRI