title: Diffusion tensor imaging in acute-to-subacute traumatic brain injury: a longitudinal analysis.
abstract: BACKGROUND
  Diffusion tensor imaging (DTI) may have prognostic utility in patients with traumatic brain injury (TBI), but the optimal timing of DTI data acquisition is unknown because of dynamic changes in white matter water diffusion during the acute and subacute stages of TBI. We aimed to characterize the direction and magnitude of early longitudinal changes in white matter fractional anisotropy (FA) and to determine whether acute or subacute FA values correlate more reliably with functional outcomes after TBI.
  
  
  METHODS
  From a prospective TBI outcomes database, 11 patients who underwent acute (≤7 days) and subacute (8 days to rehabilitation discharge) DTI were retrospectively analyzed. Longitudinal changes in FA were measured in 11 white matter regions susceptible to traumatic axonal injury. Correlations were assessed between acute FA, subacute FA and the disability rating scale (DRS) score, which was ascertained at discharge from inpatient rehabilitation.
  
  
  RESULTS
  FA declined from the acute-to-subacute period in the genu of the corpus callosum (0.70 ± 0.02 vs. 0.55 ± 0.11, p < 0.05) and inferior longitudinal fasciculus (0.54+/-0.07 vs. 0.49+/-0.07, p < 0.01). Acute correlations between FA and DRS score were variable: higher FA in the body (R = -0.78, p = 0.02) and splenium (R = -0.83, p = 0.003) of the corpus callosum was associated with better outcomes (i.e. lower DRS scores), whereas higher FA in the genu of the corpus callosum (R = 0.83, p = 0.02) corresponded with worse outcomes (i.e. higher DRS scores). In contrast, in the subacute period higher FA in the splenium correlated with better outcomes (R = -0.63, p < 0.05) and no inverse correlations were observed.
  
  
  CONCLUSIONS
  White matter FA declined during the acute-to-subacute stages of TBI. Variability in acute FA correlations with outcome suggests that the optimal timing of DTI for TBI prognostication may be in the subacute period.
authors.affiliation: Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. bedlow@mgh.harvard.edu.|Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA. bedlow@mgh.harvard.edu.
authors.forename: Brian L
authors.initials: BL
authors.lastname: Edlow
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. wcopen@partners.org.
authors.forename: William A
authors.initials: WA
authors.lastname: Copen
authors.affiliation: Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. sizzy@mgh.harvard.edu.
authors.forename: Saef
authors.initials: S
authors.lastname: Izzy
authors.affiliation: Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. khamidb@gmail.com.
authors.forename: Khamid
authors.initials: K
authors.lastname: Bakhadirov
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA. andre@nmr.mgh.harvard.edu.
authors.forename: Andre
authors.initials: A
authors.lastname: van der Kouwe
authors.affiliation: Department of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital, Harvard Medical School, Boston, MA, USA. mglenn@mgh.harvard.edu.
authors.forename: Mel B
authors.initials: MB
authors.lastname: Glenn
authors.affiliation: Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. sgreenberg@mgh.harvard.edu.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Greenberg
authors.affiliation: Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. david.greer@yale.edu.|Department of Neurology, Yale-New Haven Hospital, Yale School of Medicine, New Haven, CT, USA. david.greer@yale.edu.
authors.forename: David M
authors.initials: DM
authors.lastname: Greer
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. ona@nmr.mgh.harvard.edu.|Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA. ona@nmr.mgh.harvard.edu.
authors.forename: Ona
authors.initials: O
authors.lastname: Wu
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000368:Aged; D001930:Brain Injuries / Q000175:diagnosis*; D003337:Corpus Callosum / Q000473:pathology*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D066127:White Matter / Q000473:pathology*; D055815:Young Adult