title: The optimal trackability threshold of fractional anisotropy for diffusion tensor tractography of the corticospinal tract.
abstract: OBJECTIVE
  In order to ensure that three-dimensional diffusion tensor tractography (3D-DTT) of the corticospinal tract (CST), is performed accurately and efficiently, we set out to find the optimal lower threshold of fractional anisotropy (FA) below which tract elongation is terminated (trackability threshold).
  
  
  METHODS
  Thirteen patients with acute or early subacute ischemic stroke causing motor deficits were enrolled in this study. We performed 3D-DTT of the CST with diffusion tensor MR (magnetic resonance) imaging. We segmented the CST and established a cross-section of the CST in a transaxial plane as a region of interest. Thus, we selectively measured the FA values of the right and left corticospinal tracts at the level of the cerebral peduncle, the posterior limb of the internal capsule, and the centrum semiovale. The FA values of the CST were also measured on the affected side at the level where the clinically relevant infarction was present in isotropic diffusion-weighted imaging.
  
  
  RESULTS
  3D-DTT allowed us to selectively measure the FA values of the CST. Among the 267 regions of interest we measured, the minimum FA value was 0.22. The FA values of the CST were smaller and more variable in the centrum semiovale than in the other regions. The mean minus twice the standard deviation of the FA values of the CST in the centrum semiovale was calculated at 0.22 on the normal unaffected side and 0.16 on the affected side.
  
  
  CONCLUSIONS
  An FA value of about 0.20 was found to be the optimal trackability threshold.
authors.affiliation: Department of Radiology, Graduate School of Medicine, Tokyo University, Hongo, Tokyo. akrk-tky@umin.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Kunimatsu
authors.forename: Shigeki
authors.initials: S
authors.lastname: Aoki
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Masutani
authors.forename: Osamu
authors.initials: O
authors.lastname: Abe
authors.forename: Naoto
authors.initials: N
authors.lastname: Hayashi
authors.forename: Harushi
authors.initials: H
authors.lastname: Mori
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Masumoto
authors.forename: Kuni
authors.initials: K
authors.lastname: Ohtomo
mesh_terms: D000368:Aged; D016880:Anisotropy; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D011712:Pyramidal Tracts / Q000473:pathology*; D020521:Stroke / Q000473:pathology*