title: Longitudinal Diffusion Tensor Imaging Detects Recovery of Fractional Anisotropy Within Traumatic Axonal Injury Lesions.
abstract: Traumatic axonal injury (TAI) may be reversible, yet there are currently no clinical imaging tools to detect axonal recovery in patients with traumatic brain injury (TBI). We used diffusion tensor imaging (DTI) to characterize serial changes in fractional anisotropy (FA) within TAI lesions of the corpus callosum (CC). We hypothesized that recovery of FA within a TAI lesion correlates with better functional outcome.
  
  
  
  Patients who underwent both an acute DTI scan (≤day 7) and a subacute DTI scan (day 14 to inpatient rehabilitation discharge) at a single institution were retrospectively analyzed. TAI lesions were manually traced on the acute diffusion-weighted images. Fractional anisotropy (FA), apparent diffusion coefficient (ADC), axial diffusivity (AD), and radial diffusivity (RD) were measured within the TAI lesions at each time point. FA recovery was defined by a longitudinal increase in CC FA that exceeded the coefficient of variation for FA based on values from healthy controls. Acute FA, ADC, AD, and RD were compared in lesions with and without FA recovery, and correlations were tested between lesional FA recovery and functional recovery, as determined by disability rating scale score at discharge from inpatient rehabilitation.
  
  
  
  Eleven TAI lesions were identified in 7 patients. DTI detected FA recovery within 2 of 11 TAI lesions. Acute FA, ADC, AD, and RD did not differ between lesions with and without FA recovery. Lesional FA recovery did not correlate with disability rating scale scores.
  
  
  
  In this retrospective longitudinal study, we provide initial evidence that FA can recover within TAI lesions. However, FA recovery did not correlate with improved functional outcomes. Prospective histopathological and clinical studies are needed to further elucidate whether lesional FA recovery indicates axonal healing and has prognostic significance.
authors.affiliation: Department of Neurology, Massachusetts General Hospital, Harvard Medical School, 175 Cambridge Street - Suite 300, Boston, MA, 02114, 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.
authors.forename: William A
authors.initials: WA
authors.lastname: Copen
authors.affiliation: Department of Neurology, Massachusetts General Hospital, Harvard Medical School, 175 Cambridge Street - Suite 300, Boston, MA, 02114, USA.
authors.forename: Saef
authors.initials: S
authors.lastname: Izzy
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.|Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Andre
authors.initials: A
authors.lastname: van der Kouwe
authors.affiliation: Department of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Mel B
authors.initials: MB
authors.lastname: Glenn
authors.affiliation: Department of Neurology, Massachusetts General Hospital, Harvard Medical School, 175 Cambridge Street - Suite 300, Boston, MA, 02114, USA.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Greenberg
authors.affiliation: Department of Neurology, Yale-New Haven Hospital, Yale School of Medicine, New Haven, CT, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Greer
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.|Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Ona
authors.initials: O
authors.lastname: Wu
mesh_terms: D000293:Adolescent; D000328:Adult; D016880:Anisotropy; D000070642:Brain Injuries, Traumatic / Q000000981:diagnostic imaging*; D002675:Child, Preschool; D003337:Corpus Callosum / Q000000981:diagnostic imaging* / Q000293:injuries*; D020833:Diffuse Axonal Injury / Q000000981:diagnostic imaging*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D055815:Young Adult
keywords: Apparent diffusion coefficient; Diffusion tensor imaging; Fractional anisotropy; Traumatic axonal injury; Traumatic brain injury