title: Recovery of accurate T2from historical 1.5 tesla proton density and T2-weighted images: Application to 7-year T2changes in multiple sclerosis brain.
abstract: To determine accurate quantitative transverse relaxation times (T2) using retrospective clinical images and apply it to examine 7-year changes in multiple sclerosis (MS) brain.
  
  
  
  A method for T2mapping from retrospective proton density (PD) and T2-weighted fast spin echo images was recently introduced, but requires measurement of flip angles. We examined whether 1.5T flip angle variation in brain can be predicted, thus enabling T2analysis of historical PD and T2-weighted images without a concurrent flip angle map. After method validation in healthy volunteers, retrospective longitudinal T2analysis was performed in 14 MS subjects over seven years. Changes in patient T2values were compared with brain atrophy, T2lesion load and disability score in MS.
  
  
  
  Similar flip angle maps across volunteers enabled retrospective T2from PD and T2-weighted images even when different refocusing angles were used. Over seven years, significant T2changes of 2-4% were observed when using T2modelling and the 7-year effect size for globus pallidus T2was 0.56, which was more significant than brain atrophy. No significant T2results were found when using exponential fit, which cannot account for refocusing angle variation. Moreover, change is T2in globus pallidus and internal capsule correlated with MS disability score over time when using T2modelling.
  
  
  
  Accurate quantitative T2can be extracted from standard clinical 1.5T MRI exams that include PD and T2-weighted imaging even when no flip angle map is available. This method was applied retrospectively to examine seven year changes in MS.
authors.affiliation: Department of Biomedical Engineering, University of Alberta, Edmonton, Canada.
authors.forename: Md Nasir
authors.initials: MN
authors.lastname: Uddin
authors.affiliation: Department of Physics, University of Alberta, Edmonton, Canada.
authors.forename: Kelly C
authors.initials: KC
authors.lastname: McPhee
authors.affiliation: Division of Neurology, Department of Medicine, University of Alberta, Edmonton, Canada.
authors.forename: Gregg
authors.initials: G
authors.lastname: Blevins
authors.affiliation: Department of Biomedical Engineering, University of Alberta, Edmonton, Canada. Electronic address: wilman@ualberta.ca.
authors.forename: Alan H
authors.initials: AH
authors.lastname: Wilman
mesh_terms: D000328:Adult; D001284:Atrophy / Q000473:pathology; D001921:Brain / Q000000981:diagnostic imaging* / Q000473:pathology; D001927:Brain Diseases / Q000473:pathology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000000981:diagnostic imaging* / Q000473:pathology; D011522:Protons; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012720:Severity of Illness Index
chemical_list: D011522:Protons
keywords: Atrophy; B(1) mapping; Brain iron; Multiple sclerosis; Proton density; T(2) mapping; T(2)-weighting