title: Characterizing brain structures and remodeling after TBI based on information content, diffusion entropy.
abstract: BACKGROUND
  To overcome the limitations of conventional diffusion tensor magnetic resonance imaging resulting from the assumption of a Gaussian diffusion model for characterizing voxels containing multiple axonal orientations, Shannon's entropy was employed to evaluate white matter structure in human brain and in brain remodeling after traumatic brain injury (TBI) in a rat.
  
  
  METHODS
  Thirteen healthy subjects were investigated using a Q-ball based DTI data sampling scheme. FA and entropy values were measured in white matter bundles, white matter fiber crossing areas, different gray matter (GM) regions and cerebrospinal fluid (CSF). Axonal densities' from the same regions of interest (ROIs) were evaluated in Bielschowsky and Luxol fast blue stained autopsy (n = 30) brain sections by light microscopy. As a case demonstration, a Wistar rat subjected to TBI and treated with bone marrow stromal cells (MSC) 1 week after TBI was employed to illustrate the superior ability of entropy over FA in detecting reorganized crossing axonal bundles as confirmed by histological analysis with Bielschowsky and Luxol fast blue staining.
  
  
  RESULTS
  Unlike FA, entropy was less affected by axonal orientation and more affected by axonal density. A significant agreement (r = 0.91) was detected between entropy values from in vivo human brain and histologically measured axonal density from post mortum from the same brain structures. The MSC treated TBI rat demonstrated that the entropy approach is superior to FA in detecting axonal remodeling after injury. Compared with FA, entropy detected new axonal remodeling regions with crossing axons, confirmed with immunohistological staining.
  
  
  CONCLUSIONS
  Entropy measurement is more effective in distinguishing axonal remodeling after injury, when compared with FA. Entropy is also more sensitive to axonal density than axonal orientation, and thus may provide a more accurate reflection of axonal changes that occur in neurological injury and disease.
authors.affiliation: Department of Neurology, Henry Ford Hospital, Detroit, Michigan, United States of America ; Department of Physics, Oakland University, Rochester, Michigan, United States of America.
authors.forename: Niloufar
authors.initials: N
authors.lastname: Fozouni
authors.forename: Michael
authors.initials: M
authors.lastname: Chopp
authors.forename: Siamak P
authors.initials: SP
authors.lastname: Nejad-Davarani
authors.forename: Zheng Gang
authors.initials: ZG
authors.lastname: Zhang
authors.forename: Norman L
authors.initials: NL
authors.lastname: Lehman
authors.forename: Steven
authors.initials: S
authors.lastname: Gu
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ueno
authors.forename: Mei
authors.initials: M
authors.lastname: Lu
authors.forename: Guangliang
authors.initials: G
authors.lastname: Ding
authors.forename: Lian
authors.initials: L
authors.lastname: Li
authors.forename: Jiani
authors.initials: J
authors.lastname: Hu
authors.forename: Hassan
authors.initials: H
authors.lastname: Bagher-Ebadian
authors.forename: David
authors.initials: D
authors.lastname: Hearshen
authors.forename: Quan
authors.initials: Q
authors.lastname: Jiang
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D001369:Axons / Q000473:pathology; D001921:Brain / Q000473:pathology*; D001930:Brain Injuries / Q000175:diagnosis / Q000473:pathology*; D004058:Diffusion; D056324:Diffusion Tensor Imaging / Q000379:methods*; D019277:Entropy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011336:Probability; D051381:Rats; D055815:Young Adult