title: Automatic repositioning of MRSI voxels in longitudinal studies: impact on reproducibility of metabolite concentration measurements.
abstract: OBJECTIVE
  To study an automatic repositioning method to reduce variability in longitudinal MRSI exams based on a priori image registration. Longitudinal proton MR spectroscopic imaging ((1)H MRSI) exams to study the effects of disease or treatment are becoming increasingly common. However, one source of variability in such exams arises from imperfect relocalization of the MRSI grid in the follow-up exams.
  
  
  METHODS
  Six healthy subjects were each scanned three times during the course of 1 day. In each follow-up exam a manually placed MRSI grid was acquired in addition to the automatically repositioned MRSI grid. Then coefficients of variance between baseline and follow-up scans were calculated for N-acetylaspartate, creatine, and choline. In addition, the overall MRSI grid overlap and individual voxel overlaps were also calculated for both the visually and automatically repositioned voxels.
  
  
  RESULTS
  Streamlined workflow, reduced variability of metabolite concentration measurements, and increased voxel overlaps are noted when this automatic repositioning procedure is compared to the visual MRSI grid repositioning approach.
  
  
  CONCLUSIONS
  Our results suggest that this approach is able to improve reproducibility in longitudinal MRS exams.
authors.affiliation: Massachusetts General Hospital, A.A. Martinos Center for Biomedical Imaging, Department of Radiology and Neuroradiology Division, Charlestown, Massachusetts 02129, USA. ratai@nmr.mgh.harvard.edu
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Ratai
authors.forename: Ileana
authors.initials: I
authors.lastname: Hancu
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Blezek
authors.forename: Katherine W
authors.initials: KW
authors.lastname: Turk
authors.forename: Elkan
authors.initials: E
authors.lastname: Halpern
authors.forename: R Gilberto
authors.initials: RG
authors.lastname: González
mesh_terms: D000465:Algorithms; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D001331:Automation; D001921:Brain / Q000378:metabolism*; D002794:Choline / Q000378:metabolism; D003401:Creatine / Q000378:metabolism; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D018709:Statistics, Nonparametric
chemical_list: D001224:Aspartic Acid; C000179:N-acetylaspartate; D003401:Creatine; D002794:Choline