title: Diffusion tensor MRI reveals chronic alterations in white matter despite the absence of a visible ischemic lesion on conventional MRI: a nonhuman primate study.
abstract: OBJECTIVE
  The impact of stroke on white matter is poorly described in preclinical investigations mainly based on rodents with a low white (WM)/gray matter ratio. Using diffusion tensor imaging, we evaluated WM alterations and correlated them with sensorimotor deficits after stroke in the marmoset, a nonhuman primate that displays a WM/gray matter ratio close to that of humans.
  
  
  METHODS
  Marmosets underwent a transient brain ischemia (3-hour). Eight serial MRI examinations were made during ischemia and up to 45 days after reperfusion. The sensorimotor deficits were evaluated weekly over 45 days. To assess WM alterations, the SD of the angle of the first eigenvector projection was calculated in the cortex and in the internal and external capsules. The fiber-tracking approach was used to measure the number and the length of bundles.
  
  
  RESULTS
  Changes in the apparent diffusion coefficient and the fractional anisotropy values were similar during the temporal evolution of the lesion in the marmoset model of ischemia to that reported in patients with stroke. Despite an absence of visible lesions on T2-MRI and diffusion tensor imaging at the chronic stage, diffusion tensor MRI evidenced alterations in WM by the increase in the standard deviation of the angle of the first eigenvector projection in the cortex, internal and external capsules, and the decrease in the number of bundles of fibers tracked. The disruption of WM was strongly correlated with the chronic sensorimotor deficits.
  
  
  CONCLUSIONS
  Despite an absence of a visible ischemic lesion at the chronic stage, diffusion tensor MRI revealed disorganization of WM, which probably underlies the persistence of functional deficits.
authors: CERVOxy, Hypoxia and Cerebrovascular Pathophysiology, CI-NAPS UMR-6232, University of Caen, 59, Boulevard Henri Becquerel BP5229, Caen, France 14074.
authors: Ebeline
authors: E
authors: Bihel
authors: Simon
authors: S
authors: Roussel
authors: Jérôme
authors: J
authors: Toutain
authors: Myriam
authors: M
authors: Bernaudin
authors: Omar
authors: O
authors: Touzani
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D002545:Brain Ischemia / Q000473:pathology* / Q000503:physiopathology; D002144:Callithrix; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004195:Disease Models, Animal; D005260:Female; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D011597:Psychomotor Performance / Q000502:physiology; D011712:Pyramidal Tracts / Q000473:pathology*; D020521:Stroke / Q000473:pathology / Q000503:physiopathology