title: Quantitative characterization of the corticospinal tract at 3T.
abstract: OBJECTIVE
  White matter tract-specific imaging will probably become a major component of clinical neuroradiology. Fiber tracking with diffusion tensor imaging (DTI) is widely used, but variability is substantial. This article reports the ranges of MR imaging appearance and right-left asymmetry of healthy corticospinal tracts (CST) reconstructed with DTI.
  
  
  METHODS
  For 20 healthy volunteers, whole-brain DTI data were coregistered with maps of absolute T1 and T2 relaxation times and magnetization transfer ratio (MTR), all acquired at 3T. For each individual, the 2 reconstructed CSTs and their asymmetry were analyzed with respect to the number of fibers reconstructed; tract volume; and individual MR imaging parameters restricted to the tracts. Interscan variability was estimated by repeat imaging of 8 individuals.
  
  
  RESULTS
  Reconstructed fiber number and tract volume are highly variable, rendering them insensitive to abnormalities in disease. Individual tract-restricted MR imaging parameters are more constrained, and their population averages and normal ranges are reported. The average population asymmetry is generally zero; therefore, normal ranges for an index of asymmetry are reported. By way of example, CST-restricted MR imaging parameters and their asymmetries are shown to be abnormal in an individual with multiple sclerosis who had a lesion affecting the CST.
  
  
  CONCLUSIONS
  The results constitute a normative dataset for the following imaging parameters of the CST: T1, T2, MTR, fractional anisotropy, mean diffusivity, transverse diffusivity, and the 3 diffusion tensor eigenvalues. These data can be used to identify, characterize, and establish the significance of changes in diseases that affect the CST.
authors.affiliation: Department of Neurology, Johns Hopkins University, Baltimore, MD, USA. dreich2@jhmi.edu
authors.forename: D S
authors.initials: DS
authors.lastname: Reich
authors.forename: S A
authors.initials: SA
authors.lastname: Smith
authors.forename: C K
authors.initials: CK
authors.lastname: Jones
authors.forename: K M
authors.initials: KM
authors.lastname: Zackowski
authors.forename: P C
authors.initials: PC
authors.lastname: van Zijl
authors.forename: P A
authors.initials: PA
authors.lastname: Calabresi
authors.forename: S
authors.initials: S
authors.lastname: Mori
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011712:Pyramidal Tracts / Q000033:anatomy & histology*